Rodak's Hematology: Clinical Principles and Applications, 5th Ed.

CHAPTER 22. Bone marrow failure

Clara Lo, Bertil Glader, Kathleen M. Sakamoto*

OUTLINE

Pathophysiology of Bone Marrow Failure

Aplastic Anemia

Acquired Aplastic Anemia

Inherited Aplastic Anemia

Differential Diagnosis

Other Forms of Bone Marrow Failure

Pure Red Cell Aplasia

Congenital Dyserythropoietic Anemia

Myelophthisic Anemia

Anemia of Chronic Kidney Disease

Objectives

After completion of this chapter, the reader will be able to:

1. Describe the clinical consequences of bone marrow failure.

2. Describe the etiology of acquired and inherited aplastic anemias.

3. Discuss the pathophysiologic mechanisms of acquired and inherited aplastic anemias.

4. Describe the characteristic peripheral blood and bone marrow features in aplastic anemia.

5. Classify aplastic anemia as nonsevere, severe, or very severe based on laboratory tests.

6. Discuss treatment modalities for acquired and inherited aplastic anemia and the patients for whom each is most appropriate.

7. Differentiate among causes of pancytopenia based on laboratory tests and clinical findings.

8. Discuss the possible relationship between defects in the telomerase complex and bone marrow failure in acquired and inherited aplastic anemia.

9. Compare and contrast the pathophysiology, clinical picture, and laboratory findings in inherited aplastic anemia, transient erythroblastopenia of childhood, Diamond-Blackfan anemia, and congenital dyserythropoietic anemia.

10. Describe the mechanisms causing cytopenia in myelophthisic anemia and anemia of chronic kidney disease.

CASE STUDY

After studying the material in this chapter, the reader should be able to respond to the following case study:

A 16-year-old female presented to her pediatrician with jaundice. Her pediatrician checked liver enzyme and bilirubin levels, which were elevated. Hepatitis A, B, and C serologies were all negative. She was referred to a gastroenterologist, who diagnosed her with autoimmune hepatitis. With immunomodulatory treatment, her hepatitis improved. However, over the next several months, she noticed increasing fatigue and bruising. She also developed heavier menses, with menstrual cycles lasting up to 2 weeks in duration. Physical examination revealed pallor and scattered ecchymoses with petechiae on her chest and shoulders with no other abnormalities. Complete blood count results were as follows:

 

Patient

Reference Interval

WBCs (×109/L)

2.0

4.5–11.0

HGB (g/dL)

7.9

12.0–15.0

MCV (fL)

104

80–100

Platelets (×109/L)

15

150–450

Reticulocytes (%)

0.6

0.5–2.5

Reticulocytes (×109/L)

16

20–115

Neutrophils (×109/L)

0.5

2.3–8.1

Lymphocytes (×109/L)

0.4

0.8–4.8

Serum vitamin B12 and folate levels were within reference intervals. Bone marrow aspirate revealed mild dyserythropoiesis but normal myelopoiesis and megakaryopoiesis. Iron stain revealed normal stores. A bone marrow biopsy specimen was moderately hypocellular (15%) with a reduction in all three cell lines. There was no increase in reticulin or blasts. Cytogenetic testing revealed a normal karyotype, and results of flow cytometry for paroxysmal nocturnal hemoglobinuria (PNH) cells was negative.

1. What term is used to describe a decrease in all cell lines in the peripheral blood?

2. Which anemia of bone marrow failure should be considered?

3. How would an increase in either reticulin or blasts alter the preliminary diagnosis?

4. How would the severity of this patient’s condition be classified?

5. What treatment modality would be considered for this patient?

Pathophysiology of bone marrow failure

Bone marrow failure is the reduction or cessation of blood cell production affecting one or more cell lines. Pancytopenia—or decreased numbers of circulating red blood cells (RBCs), white blood cells (WBCs), and platelets—is seen in most cases of bone marrow failure, particularly in severe or advanced stages.

The pathophysiology of bone marrow failure includes (1) the destruction of hematopoietic stem cells due to injury by drugs, chemicals, radiation, viruses, or autoimmune mechanisms; (2) premature senescence and apoptosis of hematopoietic stem cells due to genetic mutations; (3) ineffective hematopoiesis due to stem cell mutations or vitamin B12 or folate deficiency; (4) disruption of the bone marrow microenvironment that supports hematopoiesis; (5) decreased production of hematopoietic growth factors or related hormones; and (6) the loss of normal hematopoietic tissue due to infiltration of the marrow space with abnormal cells.

The clinical consequences of bone marrow failure vary, depending on the extent and duration of the cytopenias. Severe pancytopenia can be rapidly fatal if untreated. Some patients may initially be asymptomatic, and their cytopenia may be detected during a routine blood examination. Thrombocytopenia can result in bleeding and increased bruising. Decreased RBCs and hemoglobin can result in fatigue, pallor, and cardiovascular complications. Sustained neutropenia increases the risk of life-threatening bacterial or fungal infections.

This chapter focuses on aplastic anemia, a bone marrow failure syndrome resulting from damaged or defective stem cells (mechanisms 1 and 2 listed earlier). Bone marrow failure resulting from other mechanisms may present similarly to aplastic anemia, and differentiation is discussed later. Because there are many mechanisms involved in the various bone marrow failure syndromes, accurate diagnosis is essential to ensure appropriate treatment.

Aplastic anemia

Aplastic anemia is a rare but potentially fatal bone marrow failure syndrome. In 1888, Ehrlich provided the first case report of aplastic anemia involving a patient with severe anemia, neutropenia, and a hypocellular marrow on postmortem examination.1 The name aplastic anemia was given to the disease by Vaquez and Aubertin in 1904.2 The characteristic features of aplastic anemia include pancytopenia, reticulocytopenia, bone marrow hypocellularity, and depletion of hematopoietic stem cells (Box 22-1). Approximately 80% to 85% of aplastic anemia cases are acquired, whereas 15% to 20% are inherited.3 Box 22-2provides etiologic classifications.3-5

BOX 22-1

Characteristic Features of Aplastic Anemia

Pancytopenia

Reticulocytopenia

Bone marrow hypocellularity

Depletion of hematopoietic stem cells

BOX 22-2

Etiologic Classification of Aplastic Anemia

Acquired (80% to 85% of cases)

Idiopathic (70% of cases)

Secondary (10% to 15% of cases)

Dose dependent/predictable

Cytotoxic drugs

Benzene

Radiation

Idiosyncratic

Drugs (Box 22-3)

BOX 22-3

Selected Drugs Reported to Have a Rare Association with Idiosyncratic Secondary Aplastic Anemia

Antiarthritics

Gold compounds

Penicillamine

Antibiotics

Chloramphenicol

Sulfonamides

Anticonvulsants

Carbamazepine

Hydantoins

Phenacemide

Antidepressants

Dothiepin

Phenothiazine

Antidiabetic agents

Chlorpropamide

Tolbutamide

Carbutamide

Anti-inflammatories (nonsteroidal)

Diclofenac

Fenbufen

Fenoprofen

Ibuprofen

Indomethacin

Naproxen

Phenylbutazone

Piroxicam

Sulindac

Antiprotozoals

Chloroquine

Quinacrine

Antithyroidals

Methimazole

Methylthiouracil

Carbonic anhydrase inhibitors

Methazolamide

Mesalazine

Acetazolamide

Chemicals

Insecticides

Cutting/lubricating oils

Viruses

Epstein-Barr virus

Hepatitis virus (non-A, non-B, non-C, non-G)

Human immunodeficiency virus

Miscellaneous conditions

Paroxysmal nocturnal hemoglobinuria

Autoimmune diseases

Pregnancy

Inherited (15% to 20% of cases)

Fanconi anemia

Dyskeratosis congenita

Shwachman-Bodian-Diamond syndrome

Acquired aplastic anemia

Acquired aplastic anemia is classified into two major categories: idiopathic and secondary. Idiopathic acquired aplastic anemia has no known cause. Secondary acquired aplastic anemia is associated with an identified cause. Approximately 70% of all aplastic anemia cases are idiopathic, whereas 10% to 15% are secondary.3 Idiopathic and secondary acquired aplastic anemia have similar clinical and laboratory findings. Patients may initially present with macrocytic or normocytic anemia and reticulocytopenia. Pancytopenia may develop slowly or progress at a rapid rate, with complete cessation of hematopoiesis.

Incidence

In North America and Europe, the annual incidence is approximately 1 in 500,000.6 In Asia and East Asia, the incidence is two to three times higher than in North America or Europe, which may be due to environmental and/or genetic differences.7 Aplastic anemia can occur at any age, with peak incidence at 15 to 25 years and the second highest frequency at greater than 60 years.468 There is no gender predisposition.6

Etiology

As the name indicates, the cause of idiopathic aplastic anemia is unknown. Secondary aplastic anemia is associated with exposure to certain drugs, chemicals, radiation, or infections. Cytotoxic drugs, radiation, and benzenes are responsible for 10% of secondary aplastic anemia cases and suppress the bone marrow in a predictable, dose-dependent manner.45 Depending on the dose and exposure duration, the bone marrow generally recovers after withdrawal of the agent. Alternatively, approximately 70% of cases of secondary aplastic anemia occur due to idiosyncratic reactions to drugs or chemicals. In idiosyncratic reactions, the bone marrow failure is unpredictable and unrelated to dose.4 Documentation of a responsible factor or agent in these cases is difficult, because evidence is primarily circumstantial and symptoms may occur months or years after exposure. Some drugs associated with idiosyncratic secondary aplastic anemia are listed in Box 22-3.48

Generally, idiosyncratic secondary aplastic anemia is a rare event and is likely due to a combination of genetic and environmental factors in susceptible individuals. Currently, there are no readily available tests that predict individual susceptibility to these idiosyncratic reactions. However, genetic variations in immune response pathways or metabolic enzymes may play a role.4 There is an approximately twofold higher incidence of HLA-DR2 and its major serologic split, HLA-DR15, in aplastic anemia patients compared to the general population, but the relationship of this finding to disease pathophysiology has not been elucidated.910 There are also reports that genetic polymorphisms in enzymes that metabolize benzene increase susceptibility to toxicity, even at low exposure levels.411 These include polymorphisms in glutathione S-transferase (GST) enzymes (GSTT1 and GSTM1), myeloperoxidase, nicotinamide adenine dinucleotide phosphate (reduced form, NADPH), quinine oxidoreductase 1, and cytochrome oxidase P450 2E1.11 A deficiency in GST due to the GSTT1 null genotype is overrepresented in whites, Hispanics, and Asians with aplastic anemia, with a frequency of 30%, 28%, and 75%, respectively.12 White patients with aplastic anemia also have a higher frequency (22%) of the GSTM1/GSTT1 null genotype than the general population.12 GST is important for metabolism and neutralization of chemical toxins, and deficiencies of this enzyme may increase the risk of aplastic anemia. Further study is required to assess how these genetic variations, and other yet undiscovered factors, contribute to aplastic anemia.

Acquired aplastic anemia occurs occasionally as a complication of infection with Epstein-Barr virus, human immunodeficiency virus (HIV), hepatitis virus, and human parvovirus B19.4 A history of acute non-A, non-B, or non-C hepatitis 1 to 3 months before the onset of pancytopenia is found in 2% to 10% of patients with acquired aplastic anemia.13 The acquired aplastic anemia in these cases may be mediated by such mechanisms as interferon gamma and cytokine release.13

Aplastic anemia associated with pregnancy is a rare occurrence, with fewer than 100 cases reported in the literature.14 Approximately 10% of individuals with acquired aplastic anemia have a concomitant autoimmune disease,15 and approximately 10% develop hemolytic or thrombotic manifestations of paroxysmal nocturnal hemoglobinuria (PNH).16 The overlap between acquired aplastic anemia and PNH is discussed later.

Pathophysiology

The primary lesion in acquired aplastic anemia is a quantitative and qualitative deficiency of hematopoietic stem cells. Stem cells of patients with acquired aplastic anemia have diminished colony formation in methylcellulose cultures.17 The hematopoietic stem and early progenitor cell compartment is identified by expression of CD34 surface antigens. The CD34+ cell population in the bone marrow of patients with acquired aplastic anemia can be 10% or lower than that seen in healthy individuals.17 In addition, these CD34+ cells have increased expression of Fas receptors that mediate apoptosis and increased expression of apoptosis-related genes.18-20

The bone marrow stromal cells are functionally normal in acquired aplastic anemia. They produce normal or even increased quantities of growth factors and are able to support the growth of CD34+ cells from healthy donors in culture and in vivo after transplantation.421 Individuals with aplastic anemia also have elevated serum levels of erythropoietin, thrombopoietin, granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF).22 In addition, serum levels of FLT3 ligand, a growth factor that stimulates proliferation of stem and progenitor cells, is up to 200 times higher in patients with severe aplastic anemia compared to healthy controls.2223 However, despite their elevated levels, growth factors are generally unsuccessful in correcting the cytopenias found in acquired aplastic anemia.

The severe depletion of hematopoietic stem and progenitor cells from the bone marrow may be due to direct damage to stem cells, immune damage to stem cells, or other unknown mechanisms. Direct damage to stem and progenitor cells results from DNA injury following exposure to cytotoxic drugs, chemicals, radiation, or viruses.4

Immune damage to stem cells results from exposure to drugs, chemicals, viruses, or other agents that cause an autoimmune cytotoxic T-lymphocytic destruction of stem and progenitor cells.24 An autoimmune pathophysiology was first suggested in the 1970s when aplastic anemia patients undergoing pretransplant immunosuppressive conditioning had an improvement in cell counts.25 Further evidence supporting an autoimmune pathophysiology include (1) elevated blood and bone marrow cytotoxic (CD8+) T lymphocytes with an oligoclonal expansion of specific T-cell clones26; (2) increased T cell production of such cytokines as interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), which inhibit hematopoiesis and induce apoptosis27-29; (3) upregulation of T-bet, a transcription factor that binds to the promoter of the IFN-γ gene30; (4) increased TNF-α receptors on CD34+ cells31; and (5) improvement in cytopenias after immunosuppressive therapy (IST).424 Approximately two thirds of patients with acquired aplastic anemia respond to IST.32 The nonresponders may have a severely depleted stem cell compartment or other pathophysiologic factors contributing to their cytopenias.32

Possible autoimmune mechanisms include mutation of stem cell antigens and disruption of immune regulation. Young and co-workers showed that environmental exposures may alter self-proteins, induce expression of abnormal or novel antigens, or induce an immune response that cross-reacts with self-antigens.2428 Solomou and co-workers demonstrated that CD4+CD25+FOXP3+ regulatory T cells are decreased in aplastic anemia.33 These regulatory T cells normally suppress autoreactive T cells, and a deficit of these cells may facilitate an autoimmune reaction. Furthermore, a number of individuals with aplastic anemia have single nucleotide polymorphisms in IFN-γ/+874 TT, TNF-α/–308 AA, transforming growth factor-β1/–509 TT, and interleukin-6/–174 GG.34 These polymorphisms result in cytokine overproduction and may impart a genetic susceptibility to aplastic anemia as well as contribute to its severity.34

The specific antigens responsible for triggering and sustaining the autoimmune attack on stem cells are unknown. Candidate antigens have been identified from aplastic anemia patient sera, including kinectin,35diazepam-binding inhibitor-related protein 1,36 and moesin.37 These proteins are expressed in hematopoietic progenitor cells, but their role in the pathogenesis of aplastic anemia requires further investigation.

Approximately one third of patients with acquired aplastic anemia have shortened telomeres in their peripheral blood granulocytes compared with age-matched controls.3839 Telomeres protect the ends of chromosomes from damage and erosion, and cells with abnormally short telomeres undergo proliferation arrest and premature apoptosis. Telomerase is an enzyme complex that repairs and maintains the telomeres. Approximately 10% of patients with acquired aplastic anemia and shortened telomeres have a mutation in the telomerase complex gene for either the ribonucleic acid (RNA) template (TERC) or the reverse transcriptase (TERT).39-41 The cause for shortened telomeres in the other 90% of patients may be due to stress hematopoiesis or other yet unidentified mutations.39 In stress hematopoiesis, there is an increase in progenitor cell turnover, and the telomeres become shorter with each cell division.

Approximately 4% of patients with acquired aplastic anemia and shortened telomeres have mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene.42 The SBDS gene product is involved in ribosome biogenesis, and its relationship to telomere maintenance is currently unknown.42 TERT/TERC and SBDS mutations also occur in the inherited aplastic anemias, dyskeratosis congenita (DKC) and SBDS, respectively, and some patients diagnosed with acquired aplastic anemia who have these mutations may actually have DKC or SBDS.34 Correct differentiation between acquired and inherited aplastic anemia has important implications for appropriate treatment and prognosis. Immunosuppressive therapy is not nearly as effective in inherited aplastic anemia as it is in acquired aplastic anemia. Furthermore, hematopoietic stem cell transplantation (HSCT), the only known curative treatment for DKC and SBDS and a treatment option for acquired aplastic anemia, should not be performed with human leukocyte antigen (HLA)–matched siblings who test positive for the same genetic mutation.39 Brummerndorf and colleagues reported that shortened telomeres occur more often in patients whose pancytopenia does not respond to immunosuppressive therapy.43 Defective telomere maintenance may be another pathophysiologic mechanism of stem cell injury, imparting susceptibility to aplastic anemia after an environmental insult.3941

Clinical findings

Symptoms vary in acquired aplastic anemia, ranging from asymptomatic to severe. Patients usually present with symptoms of insidious-onset anemia, with pallor, fatigue, and weakness. Severe and prolonged anemia can result in serious cardiovascular complications, including tachycardia, hypotension, cardiac failure, and death. Symptoms of thrombocytopenia are also varied and include petechiae, bruising, epistaxis, mucosal bleeding, menorrhagia, retinal hemorrhages, intestinal bleeding, and intracranial hemorrhage. Fever and bacterial or fungal infections are unusual at initial presentation but may occur after prolonged periods of neutropenia. Splenomegaly and hepatomegaly are typically absent.

Laboratory findings

Pancytopenia is typical, although initially only one or two cell lines may be decreased. The absolute neutrophil count is decreased, and the absolute lymphocyte count may be normal or decreased. The hemoglobin is usually less than 10 g/dL, the mean cell volume (MCV) is increased or normal, and the percent and absolute reticulocyte counts are decreased. lists the diagnostic criteria for aplastic anemia by degree of severity.Table 22-1684445

TABLE 22-1

Diagnostic Criteria for Aplastic Anemia

 

MAA

SAA

VSAA

Bone marrow

Hypocellular bone marrow plus at least two of the following:

Bone marrow cellularity < 25%* plus at least two of the following:

Same as SAA

Neutrophils (×109/L)

0.5–1.5

0.2–0.5

< 0.2

Platelets (×109/L)

20–50

< 20

Same as SAA

Other

HGB ≤10 g/dL plus reticulocytes < 30 × 109/L

Reticulocytes < 20 × 109/L or < 1% corrected for HCT

Same as SAA

* Or 25% to 50% cellularity with < 30% residual hematopoietic cells.

HGB, Hemoglobin; HCT, hematocrit; MAA, moderate aplastic anemia; SAA, severe aplastic anemia; VSAA, very severe aplastic anemia; g, grams; dL, deciliter; L, liter.

Neutrophils, monocytes, and platelets are decreased in the peripheral blood, and the red blood cells are macrocytic or normocytic (). Toxic granulation may be observed in the neutrophils, but the RBCs and platelets are usually normal in appearance. Leukemic blasts and other immature blood cells are characteristically absent. The serum iron level and percent transferrin saturation are increased, which reflects decreased iron use for erythropoiesis. Liver function test results may be abnormal in cases of hepatitis-associated aplastic anemia. Figure 22-1

Image 

FIGURE 22-1 Peripheral blood film for a patient with aplastic anemia (×500). Note occasional macrocytes and absence of white blood cells and platelets.

Approximately two thirds of patients have small numbers (less than 25%) of PNH clones in the peripheral blood,46 but only 10% of patients develop a sufficient number of PNH cells to have the clinical and biochemical manifestations of PNH disease.16 PNH is characterized by an acquired stem cell mutation resulting in lack of the glycosylphosphatidylinositol (GPI)-linked proteins CD55 and CD59. The absence of CD55 and CD59 on the surface of the RBCs renders them more susceptible to complement-mediated cell lysis. It is important to test for PNH in acquired aplastic anemia because of the increased risk of hemolytic and/or thrombotic complications (Chapter 24). Historically, PNH diagnosis depended on the Ham acid hemolysis test: patients’ cells were placed in acidified serum, and a positive result demonstrated lysis of RBCs. However, this test was poorly sensitive, because complement-mediated hemolysis was detected only in the presence of large numbers of circulating PNH cells. Currently, flow cytometric analysis for CD59 on RBCs and CD24 and CD14 on granulocytes and monocytes is used as a more sensitive diagnostic method and has replaced the Ham test in nearly all laboratories (Chapter 24).84647

Bone marrow aspirate and biopsy specimens have prominent fat cells with areas of patchy marrow cellularity. Biopsy samples are required for accurate quantitative assessment of marrow cellularity, and severe hypocellularity is a characteristic feature of aplastic anemia (). Erythroid, granulocytic, and megakaryocytic cells are decreased or absent. Dyserythropoiesis may be present, but there is typically no dysplasia of the granulocyte or platelet cell lines. Blasts and other abnormal cell infiltrates are characteristically absent. Reticulin staining is usually normal. Figure 22-2

Image 

FIGURE 22-2A, Normal bone marrow tissue section (hematoxylin and eosin stain). B, Hypoplastic bone marrow tissue section from a patient with aplastic anemia (hematoxylin and eosin stain). (Courtesy Ann Bell, University of Tennessee, Memphis.)

In patients receiving immunosuppressive therapy, the risk of developing an abnormal karyotype is 14% at 5 years and 20% at 10 years.48 Monosomy 7 and trisomy 8 are the most common cytogenetic abnormalities.4748 Cytogenetic analysis using conventional culture techniques often underestimates the incidence of karyotype abnormalities because of bone marrow hypocellularity and scarcity of cells in metaphase.49 Alternatively, interphase fluorescence in situ hybridization (FISH) using deoxyribonucleic acid (DNA) probes for specific chromosome abnormalities may be used. In comparison to conventional cytogenetic analysis, FISH has greater sensitivity in the detection of chromosome abnormalities and can also be performed using nondividing cells.49 In a study performed by Kearns and colleagues, FISH detected monosomy 7 or trisomy 8 in 26% of aplastic anemia patients who had a normal karyotype by conventional cytogenetic testing.49

Patients with inherited aplastic anemia may be misdiagnosed with acquired aplastic anemia if symptoms manifest in late adolescence or adulthood or if the patients lack the typical clinical and physical characteristics of an inherited marrow failure syndrome (e.g., abnormal thumbs, short stature).34 Consideration of inherited aplastic anemia syndromes in the differential diagnosis of acquired aplastic anemia is essential, because these conditions require a different therapeutic approach. The inherited aplastic anemia syndromes are discussed later in the chapter.

Treatment and prognosis

Severe acquired aplastic anemia requires immediate attention to prevent serious complications. If a causative agent is identified, its use should be discontinued. Blood product replacement should be given judiciously to avoid alloimmunization.8 Platelets should not be transfused at levels greater than 10,000/μL, unless the patient is bleeding.8

One of the most important early decisions is determining whether the patient is a candidate for hematopoietic stem cell transplantation (HSCT). HSCT is the treatment of choice for patients with severe aplastic anemia who are younger than 40 years of age and have a human leukocyte antigen (HLA)-identical sibling.48 Unfortunately, only 20% to 30% of patients meet these criteria.4 Therefore, IST, consisting of antithymocyte globulin and cyclosporine, is used for patients older than 40 years of age and for patients without an HLA-identical sibling.816 Antithymocyte globulin decreases the number of activated T cells, and cyclosporine inhibits T-cell function, thereby suppressing the autoimmune reaction against the stem cells. Approximately two thirds of patients initially respond to IST; unfortunately, 30% to 40% relapse.1632 For patients with severe acquired aplastic anemia who are not responsive to IST, a second course of IST or an HSCT from an HLA-matched unrelated donor is an option, but survival is not as high as with HSCT from an HLA-identical sibling.850 The response rate for a second course of IST is approximately 65% for those who experienced relapse and 30% for those whose disorder was initially refractive to IST.51Individuals with PNH cells (CD55 CD59) are almost twice as likely to respond to IST than are those who lack these cells.46 In addition, the presence of both PNH cells and HLA-DR2 increases the likelihood of response by 3.5-fold.52 Granulocyte colony-stimulating factor (G-CSF), other hematopoietic growth factors, and steroids do not increase overall survival or improve the response rate; therefore, they are not recommended for routine use.85354

Other supportive therapy includes antibiotic and antifungal prophylaxis in cases of prolonged neutropenia. Patients with mild to moderate aplastic anemia may not require treatment but must be monitored periodically for pancytopenia and abnormal cells.

The overall outcome for patients with acquired aplastic anemia has dramatically improved in the past 2 decades. Among patients who receive an HSCT from an HLA-identical sibling, 91% of children and 74% of adults achieve 10-year overall survival.50 Those percentages decrease slightly to 75% of children and 63% of adults when the bone marrow transplant is from an HLA-matched unrelated donor.50 In patients treated with IST, 75% of children and 63% of adults achieve 10-year survival.50 Additional outcomes in the IST-treated patients include a 10-year risk of developing hemolytic or thrombotic PNH and a 10% to 20% risk of myelodysplastic syndrome (MDS) or leukemia.1647 Development of monosomy 7 predicts poor outcome, with a greater likelihood of unresponsiveness to IST and progression to MDS or leukemia.48

Inherited aplastic anemia

In comparison with acquired aplastic anemia, patients with inherited aplastic anemia present at an earlier age and may have characteristic physical stigmata. The three inherited diseases for which bone marrow failure and pancytopenia are a consistent feature are Fanconi anemia, dyskeratosis congenita, and Shwachman-Bodian-Diamond syndrome.

Fanconi anemia

Fanconi anemia (FA) is a chromosome instability disorder characterized by aplastic anemia, physical abnormalities, and cancer susceptibility. In 1927, Dr. Guido Fanconi first described this syndrome in three brothers with skin pigmentation, short stature, and hypogonadism.55 FA has a prevalence of 1 to 5 cases per million.56 The carrier rate is 1 in 300 in the United States and Europe, with a threefold higher prevalence in Ashkenazi Jews and South African Africaners.57 FA is the most common of the inherited aplastic anemias.

Clinical findings. 

Patients with FA have variable features and symptoms. Physical malformations may be present at birth, though hematologic abnormalities may not appear until older childhood or adulthood. Furthermore, only two thirds of patients have physical malformations.358 These anomalies vary considerably, though there is a higher frequency of skeletal abnormalities (thumb malformations, radial hypoplasia, microcephaly, hip dislocation, and scoliosis); skin pigmentation (hyperpigmentation, hypopigmentation, café-au-lait lesions); short stature; and abnormalities of the eyes, kidneys, and genitals.56-58 Low birth weight and developmental delay are also common.

The symptoms associated with pancytopenia usually become apparent at 5 to 10 years of age, though some patients may not present until adulthood.357 Individuals with FA also have an increased cancer risk. This includes an increased incidence of leukemia in childhood and solid tumors (e.g., oral, esophageal, anogenital, cervical) in adulthood.59 In approximately 5% of cases, a malignancy is diagnosed before the FA is recognized.59

Genetics and pathophysiology. 

There are currently 15 reported genes associated with FA: FANCA, FANCB, FANCC, FANCD1 (also called BRCA2), FANCD2, FANCE, FANCF, FANCG (also called XRCC9), FANCI, FANCJ (also called BRIP1/BACH1), FANCL, FANCM, FANCN (also called PALB2), FANCO (also called RAD51C), and FANCP (also called SLX4).56 Patients with FA typically have biallelic mutations or deletions in one of these genes. The mode of inheritance is autosomal recessive except for FANCB, which is X-linked recessive. Mutations in the FANCA gene occur with the highest frequency.358 The relationship between mutations in the FA genes and disease pathology is not clear. Cells are highly susceptible to chromosome breakage after exposure to DNA cross-linking agents. FA cells may also have accelerated telomere shortening and apoptosis, a late S-phase cell cycle delay, hypersensitivity to oxidants, and cytokine dysregulation.3565860

The range of FA protein function is not completely known, but these proteins participate in a highly elaborate DNA damage response pathway. The FA pathway consists of a nuclear core complex, a protein ID complex, and effector proteins.5860 The FA proteins A, B, C, E, F, G, L, and M form the nuclear core complex; proteins D2 and I form the ID complex; and the effector proteins are D1, J, N, O, and P.565860 The core complex facilitates the monoubiquitylation and activation of the ID complex. The ID complex then localizes with effector DNA repair proteins at foci of DNA damage to effect DNA repair.5860

Laboratory findings. 

Laboratory results are similar to those in acquired aplastic anemia, with pancytopenia, reticulocytopenia, and a hypocellular bone marrow. Macrocytic RBCs are often the first detected abnormality, and thrombocytopenia usually precedes the development of the other cytopenias.56 Fetal hemoglobin (Hb F) may be strikingly elevated, and α-fetoprotein is also increased.56

Chromosomal breakage analysis is the diagnostic test for Fanconi anemia.56 Patients’ peripheral blood lymphocytes are cultured with the DNA cross-linking agents diepoxybutane (DEB) or mitomycin C (MMC). Compared to normal lymphocytes, FA cells have a greater number of characteristic chromosome breaks and ring chromosomes, indicating increased fragility.356 Caution must be made in interpreting peripheral blood results, because they may be negative in the 10% to 15% of FA patients who have somatic mosaicism due to a reversion of one abnormal allele to the normal type.356 To confirm the diagnosis in these cases, chromosome breakage studies can be performed on cultured skin fibroblasts from a skin biopsy specimen.5661

Treatment and prognosis. 

More than 90% of FA patients develop bone marrow failure by 40 years of age.59 Furthermore, one third of patients develop MDS and/or acute myeloid leukemia (AML) by a median age of 14 years, and 25% develop solid tumors by a median age of 26 years.5962 Squamous cell carcinomas of the head and neck, anogenital region, and skin are the most common solid tumors, followed by tumors of the liver, brain, and kidney.59 Patients with FA have an increased risk of developing vulvar cancer (4300-fold), esophageal cancer (2300-fold), AML (800-fold), and head/neck cancer (700-fold) compared with the general population.63Approximately 3% of patients develop more than one type of malignancy.62 Left untreated, death by 20 years of age secondary to bone marrow failure or malignancy is common. Patients with mutations in theFANCC gene experience bone marrow failure at a particularly young age and have the poorest survival.62 Increased telomere shortening in FA cells is associated with more severe pancytopenia and a higher risk of malignancy. However, the precise role of telomere shortening in the evolution of bone marrow failure and cancer is currently unclear.64

Supportive treatment for cytopenia includes transfusions and administration of cytokines (G-CSF and GM-CSF).5657 The only curative treatment is HSCT, preferably from an HLA-identical sibling. It is important to screen donor siblings for FA prior to transplant. Patients should also have decreased intensity pretransplant conditioning because of their underlying chromosomal instability.5662 Gene therapy has been attempted in clinical trials but has not been successful.

Dyskeratosis congenita

Dyskeratosis congenita (DKC) is a rare inherited bone marrow failure syndrome with fewer than 600 known cases worldwide.5665

Clinical findings. 

DKC is characterized by mucocutaneous abnormalities, bone marrow failure, and pancytopenia. The typical clinical presentation involves a triad of abnormal skin pigmentation, dystrophic nails, and oral leukoplakia. Skin and nail findings usually appear before 10 years of age.356 Median age of diagnosis is 15 years.66 By 30 years of age, 80% to 90% of patients have bone marrow abnormalities.3 Patients can also manifest a wide range of multisystem abnormalities, including pulmonary fibrosis, liver disease, developmental delay, short stature, microcephaly, prematurely gray hair or hair loss, immunodeficiency, dental caries, and periodontal disease.66 Patients have a 40% risk of cancer by 50 years of age, most commonly AML, MDS, and epithelial malignancies.65

Genetics and pathophysiology. 

DKC chromosomes have very short telomeres, and inherited defects in the telomerase complex are implicated in the pathophysiology.66 The telomerase complex synthesizes telomere repeats to elongate chromosome ends, maintaining the telomere length needed for cell survival.

There are currently eight different genes implicated in DKC, and it can be inherited in three different patterns: X-linked recessive, autosomal dominant, and autosomal recessive.35666 The best-characterized form results from one or more mutations on the long arm of the X-chromosome on the DKC1 gene dyskerin. Dyskerin is a ribonucleoprotein involved in RNA processing, and it associates with TERC (telomerase RNA component) in the telomerase complex. The autosomal dominant form is due to mutations in the genes that encode TERC, TERT (telomerase enzyme), or TINF2 (component of the shelterin complex that regulates telomere length).66 In the autosomal recessive form, mutations in TERT, NHP2, NOP10, WRAP53, and CTC1 have been identified.66 The proteins encoded by these genes are also involved in telomere maintenance. Although the exact pathophysiologic mechanisms are still unknown, the shortened telomeres in DKC cause premature death in the rapidly dividing cells in the bone marrow and epithelium and likely lead to genomic instability and a predisposition to cancer.35667

Laboratory findings. 

Pancytopenia and macrocytic RBCs are typical peripheral blood findings. The fetal hemoglobin level may also be increased. Only about 40% of patients have an identified mutation in one of the eight known telomerase complex genes.67 A new flow fluorescence in situ hybridization (FISH) test for detection of very short telomeres in WBC subsets has been proposed as a diagnostic test for those with suspected DKC who lack mutations in known genes.67 Patients with FA, SBDS, and acquired aplastic anemia may also have cells with shortened telomeres, though they are not found in multiple WBC subsets.67 In contrast, DKC cells often have shortened telomeres in several WBC subsets, including naive T cells and B cells.

Treatment and prognosis. 

Median survival for patients with DKC is 42 years.65 Approximately 60% to 70% of deaths are due to bone marrow failure complications. Ten percent to 15% of deaths result from severe pulmonary disease, and 10% of deaths result from malignancies.356 Treatment with bone marrow transplantation has not been optimal because of the high incidence of fatal pulmonary fibrosis and vascular complications.366 Although androgen therapy produces a transient response in 50% to 70% of patients, it does not halt the progression of the bone marrow failure.3

Shwachman-bodian-diamond syndrome

Shwachman-Bodian-Diamond syndrome (SBDS) is an inherited multisystem disorder characterized by pancreatic insufficiency, cytopenia, skeletal abnormalities, and a predisposition for hematologic malignancies. The incidence has been estimated to be approximately 8.5 cases per 1 million live births.56

Clinical findings. 

Patients with SBDS have peripheral blood cytopenia and decreased pancreatic enzyme secretion.45 The pancreatic insufficiency causes gastrointestinal malabsorption, which typically presents in early infancy.3Patients have neutropenia and immune dysfunction and are at increased risk of severe infections and sepsis.4568 Nearly all SBDS patients have delayed bone maturation, and approximately 50% have failure to thrive and short stature.4569

Genetics and pathophysiology. 

SBDS is an autosomal recessive disorder, and 90% of patients have biallelic mutations in the SBDS gene.34568 The SBDS gene is involved in ribosome metabolism and mitotic spindle stability,70 but its relationship to the disease manifestations is currently unknown. There are quantitative and qualitative deficiencies in CD34+ cells, dysfunctional bone marrow stromal cells, increased apoptosis and mitotic spindle destabilization in hematopoietic cells, and short telomeres in peripheral blood granulocytes.3456870

Laboratory findings. 

Nearly all patients with SBDS have neutropenia (less than 1.5 × 109 neutrophils/L).71 Half of the patients also develop anemia or thrombocytopenia, and one fourth develop pancytopenia.71 The RBCs are usually normocytic but can be macrocytic, and approximately two thirds of patients have elevated Hb F.4571 The bone marrow is usually hypocellular but can be normal or even hypercellular. Due to the pancreatic insufficiency, 72-hour fecal fat testing shows increased fat excretion, and serum trypsinogen and isoamylase levels are decreased compared with age-related reference intervals.68 In comparison to cystic fibrosis, which can have a similar malabsorption presentation, patients with SBDS have normal sweat chloride tests. Testing for the SBDS gene mutation is commercially available and should be done in suspected patients and their parents.

Treatment and prognosis. 

In some cases no treatment of hematologic features is required. However, if needed, treatment consists of G-CSF for neutropenia, transfusion support for anemia and thrombocytopenia, and enzyme replacement for pancreatic insufficiency. The risk of AML and MDS is approximately 19% at 20 years and 36% at 30 years.72 Allogeneic bone marrow transplantation is recommended in cases of severe pancytopenia, AML, or MDS. Unfortunately, despite supportive care and attempted curative therapy, 5-year overall survival is 60% to 65%, with many deaths occurring from severe infections and malignancy.4568 Poor outcomes after HSCT occur due to graft failure, transplant-related toxicities, and recurrent leukemia.68

Differential diagnosis

A distinction must be made between acquired aplastic anemia, inherited aplastic anemia, and other causes of pancytopenia, including PNH, MDS, megaloblastic anemia, and leukemia. The importance of a correct diagnosis is clear, as diagnostic conclusions dictate therapeutic management and prognosis. The distinguishing features of these conditions are listed in and Tables 22-222-3.38

TABLE 22-2

Differentiation of Aplastic Anemia from Other Causes of Pancytopenia

Condition

Peripheral Blood

Bone Marrow

Laboratory Test Results

Clinical Findings

Failure of Bone Marrow to Produce Blood Cells

Aplastic anemia

No immature WBCs or RBCs; ↓ reticulocytes; MCV ↑ or normal

Hypocellular; blasts and abnormal cells absent; reticulin normal; RBC dyspoiesis may be present; WBC and platelet dyspoiesis absent

Acquired: PNH cells* may be present; chromosome abnormalities may be present Inherited: Table 22-3

Splenomegaly absent

Increased Destruction of Blood Cells

PNH

Reticulocytes ↑; MCV normal or ↑; nucleated RBCs present or absent

Erythroid hyperplasia; may be hypocellular

PNH cells* present; hemoglobinuria +/–; chromosome abnormalities may be present

Splenomegaly absent; thrombosis may be present

Ineffective Hematopoiesis

Myelodysplastic syndrome

Variable pancytopenia; reticulocytes ↓; MCV normal or ↑; blasts and abnormal WBCs, RBCs, and platelets may be present

Hypercellular; 20% of cases hypocellular; dyspoiesis in one or more cell lines present; blasts and immature cells present; reticulin ↑

Chromosome abnormalities usually present

Splenomegaly uncommon

Megaloblastic anemias

MCV ↑; oval macrocytes; hypersegmented neutrophils

Hypercellular with megaloblastic features

Serum vitamin B12 or folate or both ↓

Splenomegaly absent

Bone Marrow Infiltration

Acute leukemia

Blasts present

Hypercellular; blasts ↑; reticulin ↑

Chromosome abnormalities may be present

Splenomegaly may be present

Hairy cell leukemia

Hairy cells present; monocytes ↓

Hairy cells and fibrosis present; reticulin ↑

Hairy cells present; TRAP +

Splenomegaly present (60–70% of cases)

TABLE 22-3

Key Characteristics of Inherited/Congenital Bone Marrow Failure Anemias

Condition

Genetics*

Peripheral Blood

Bone Marrow

Laboratory Test Results

Clinical Findings

Due to Bone Marrow Hypoplasia

FA

AR, XLR 15 genes

Pancytopenia; reticulocytes ↓; MCV ↑

Hypocellular with ↓ in all cell lines

Chromosome breakage with DEB/MMC; Hb F may be ↑

Physical malformations may be present; risk of cancers, leukemia, myelodysplastic syndrome

DKC

AR, XLR, AD 8 genes

Pancytopenia; reticulocytes ↓; MCV ↑

Hypocellular with ↓ in all cell lines

75% have mutations in TERC, TERT, DKC1, TINF2, NHP2, NOP10, WRAP53, or CTC1; Hb F may be ↑; very short telomeres in lymphocyte subsets

Physical malformations may be present; pulmonary disease; risk of cancers, leukemia, myelodysplastic syndrome

SBDS

AR 1 gene

Neutropenia; pancytopenia (25% of cases); reticulocytes ↓; MCV normal or ↑

Hypocellular, normocellular, or hypercellular

90% have mutations in SBDS gene; serum trypsinogen and isoamylase ↓ for age; Hb F may be ↑

Pancreatic insufficiency; physical malformations may be present; risk of infections, leukemia, myelodysplastic syndrome

DBA

AD (50% of cases) 9 genes

Anemia; reticulocytes ↓; MCV ↑

Erythroid hypoplasia

Erythrocyte adenosine deaminase ↑; Hb F may be ↑; 25% have mutations in RPS19 gene; another 25% have mutations in RPS7, RPS10, RPS17, RPS24, RPS26, RPL5, RPL11, or RPL35A

Physical malformations may be present; risk of cancers, leukemia, myelodysplastic syndrome

Due to Ineffective Hematopoiesis

CDA I

AR 1 gene

Anemia; reticulocytes ↓; MCV ↑; poik, baso stipp, Cabot rings

Hypercellular; RBC precursors megaloblastoid with internuclear chromatin bridges and < 5% binucleated forms

Mutations in CDAN1 gene; spongy, “Swiss cheese” heterochromatin in erythroblasts by electron microscopy

Physical malformations may be present; iron overload; splenomegaly; hepatomegaly

CDA II

AR 1 gene

Anemia; reticulocytes ↓; MCV normal; poik, baso stipp

Hypercellular; RBC precursors normoblastic with 10% to 35% binucleated forms

Mutations in SEC23B gene; positive Ham test result (rarely done)

Physical malformations may be present; iron overload; jaundice; gallstones; splenomegaly

CDA III

AD 1 gene

Mild anemia; reticulocytes ↓; MCV ↑; poik, baso stipp

Hypercellular; RBC precursors megaloblastoid with giant multinucleated forms with up to 12 nuclei

Mutations in KIF23 gene

Treatment usually not needed

* Genes identified as of 2013; genetic discovery is ongoing.

↑, Increased; ↑, decreased; AR, autosomal recessive; AD, autosomal dominant; XLR, X-linked recessive; baso stipp, basophilic stippling; CDA, congenital dyserythropoietic anemia; DBA, Diamond-Blackfan anemia; DKC, dyskeratosis congenita; DEB, diepoxybutane; FA, Fanconi anemia; MCV, mean cell volume; MMC, mitomycin C; poik, poikilocytosis; RBC, red blood cell; SBDS, Shwachman-Bodian-Diamond syndrome; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; Hb F, fetal hemoglobin.

* PNH erythrocytes are detected by flow cytometry by their lack of expression of CD59; PNH granulocytes and monocytes lack expression of CD24, CD16, and CD14 (Chapter 24).

† Hairy cells are detected by flow cytometry by their expression of CD19, CD20, CD22, CD11c, CD25, CD103, and FMC7.

↑, Increased; ↓, decreased; +, positive result; +/–, positive or negative result; MCV, mean cell volume; PNH, paroxysmal nocturnal hemoglobinuria; RBC, red blood cell; TRAP, tartrate-resistant acid phosphatase; WBC, white blood cell.

Alternative diagnoses include lymphoma, myelofibrosis, and mycobacterial infections, which also may present with pancytopenia. However, these diagnoses often can be distinguished with a careful history, physical exam, and laboratory testing. Review of a peripheral blood film by an experienced morphologist is important. If needed, bone marrow evaluation and molecular testing for chromosome abnormalities and gene mutations can further distinguish these diagnoses. Anorexia nervosa also may present with pancytopenia. In these cases, the bone marrow is hypocellular and has a decreased number of fat cells.8 The cytopenias revert with correction of the underlying disease.

Other forms of bone marrow failure

Pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare disorder of erythropoiesis characterized by a selective and severe decrease in erythrocyte precursors in an otherwise normal bone marrow. Patients have severe anemia (usually normocytic), reticulocytopenia, and normal WBC and platelet counts. PRCA may be acquired or congenital. It is important to distinguish between acquired and congenital forms, as they require different therapeutic approaches.

Acquired pure red cell aplasia

Acquired PRCA may occur in children or adults and can be acute or chronic. Primary PRCA may be idiopathic or autoimmune-related. Secondary PRCA may occur in association with an underlying thymoma, hematologic malignancy, solid tumor, infection, chronic hemolytic anemia, collagen vascular disease, or exposure to drugs or chemicals.7374 Therapy is first directed at treatment of the underlying condition, but immunosuppressive therapy may be considered if the PRCA is not responsive. Cyclosporine is associated with a higher response rate (65% to 87%) than corticosteroids (30% to 62%) and is better suited for long-term maintenance if needed.74

The acquired form of PRCA in young children is also known as transient erythroblastopenia of childhood (TEC). A history of viral infection is found in half of patients, which is thought to trigger an immune mechanism that targets red cell production.75 The anemia is typically normocytic, and Hb F and erythrocyte adenosine deaminase levels usually are normal.7375 Red cell transfusion support is the mainstay of therapy if the child is symptomatic from anemia. Normalization of erythropoiesis occurs within weeks in the vast majority patients.75 There may be a genetic predisposition to TEC in some families.75

Congenital pure red cell aplasia: Diamond-blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid hypoplastic disorder of early infancy with an estimated incidence of 7 to 10 cases per million live births.56 Mutations have been identified in nine genes that encode structural ribosome proteins: RPS7, RPS10, RPS17, RPS19, RPS24, and RPS26 in the 40S subunit and RPL5, RPL11, and RPL35A in the 60S subunit.76 Approximately 25% of patients have a mutation in the RPS19 gene, and mutations in the other eight genes account for another 25% of cases.7677 Many mutations are still unidentified, and it is of interest that an additional 15% to 20% of cases can be accounted for by haplo-deletions of these same RPS genes.78 Mutations in these ribosomal proteins disrupt ribosome biogenesis in DBA, but the pathophysiologic mechanisms leading to the clinical manifestations are currently unknown. Nearly 50% of DBA cases are linked to an autosomal dominant inheritance pattern, but sporadic mutations have also been reported.76

Over 90% of patients show signs of the disorder during the first year of life, with a median age of 8 weeks; however, some patients with DBA are asymptomatic until adulthood.79 Approximately half of patients have characteristic physical anomalies, including craniofacial dysmorphisms, short stature, and neck and thumb malformations.5679

The characteristic peripheral blood finding is a severe macrocytic anemia with reticulocytopenia.56 The WBC count is normal or slightly decreased, and the platelet count is normal or slightly increased. Bone marrow examination distinguishes DBA from the hypocellular marrow in aplastic anemia, because there is normal cellularity of myeloid cells and megakaryocytes and hypoplasia of erythroid cells. The karyotype in DBA is normal. In most cases, Hb F and erythrocyte adenosine deaminase are increased; these findings distinguish DBA from TEC, in which these levels are normal.5676 Other features distinguishing DBA from TEC are detailed in Table 22-4.

TABLE 22-4

Distinguishing Characteristics of Diamond-Blackfan Anemia and Transient Erythroblastopenia of Childhood.

Test Result

DBA*

TEC*

Erythrocyte ADA increased at diagnosis

85%

5%

MCV increased at diagnosis

80%

5%

MCV increased in remission

80%

0%

Hb F increased at diagnosis

50%–85%

1%–2%

Hb F increased in remission

50%–85%

0%

* Percent of patients displaying the test results.

Modified from D’Andrea AD, Dahl N, Guinan EC, Shimamura A: Marrow failure. Hematology Am Soc Hematol Educ Program, 58-72, 2002.

DBA, Diamond-Blackfan anemia; TEC, transient erythroblastopenia of childhood; ADA, adenosine deaminase; MCV, mean corpuscular volume; Hb F, fetal hemoglobin.

Therapy includes RBC transfusions and corticosteroids. Although 50% to 75% of patients respond to corticosteroid therapy, side effects are severe with long-term use, including immunosuppression and growth delay.5676 Overall survival is 75% at 40 years.79 Bone marrow transplantation improves outcomes, with greater than 90% overall survival in patients younger than 10 years old transplanted with a matched-related donor, and 80% in those with a matched unrelated donor.76

Congenital dyserythropoietic anemia

The congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of rare disorders characterized by refractory anemia, reticulocytopenia, hypercellular bone marrow with markedly ineffective erythropoiesis, and distinctive dysplastic changes in bone marrow erythroblasts. Megaloblastoid development occurs in some types, but it is not related to vitamin B12 or folate deficiency. Granulopoiesis and thrombopoiesis are normal. The anemia varies from mild to moderate, even among affected siblings. Secondary hemosiderosis arises from chronic intramedullary and extramedullary hemolysis, as well as increased iron absorption associated with ineffective erythropoiesis. Iron overload develops even in the absence of blood transfusions. Jaundice, cholelithiasis, and splenomegaly are also common findings. CDAs do not progress to aplastic anemia or hematologic malignancies.80

Symptoms of CDA usually occur in childhood or adolescence but may first appear in adulthood.56 CDA is classified into three major types: CDA I, CDA II, and CDA III. There are rare variants that do not fall into these categories, and they have been assigned to four other groups: CDA IV through CDA VII.5680 Whether CDA types IV through VII actually are separate entities is a matter of some controversy. This merely may be a reflection of the insensitive tests to classify CDA disorders. Further gene mutation studies should clarify this issue.

CDA I is inherited in an autosomal recessive pattern and is characterized by a mild to severe chronic anemia. Over 150 cases have been reported.81 CDA I is caused by mutations in the CDAN1 gene on chromosome 15, which encodes codanin-1, a cell-cycle regulated nuclear protein.8283 The exact role of codanin-1 in the pathophysiology of CDA I is unknown. Malformations of fingers or toes, brown skin pigmentation, and neurologic defects are found more frequently in CDA I than in the other CDA subtypes. The hemoglobin usually ranges from 6.5 g/dL to 11.5 g/dL, with a mean of 9.5 g/dL.80 RBCs are macrocytic and may exhibit marked poikilocytosis, basophilic stippling, and Cabot rings. The erythroblasts are megaloblastoid and characteristically have internuclear chromatin bridges or nuclear stranding (Figure 22-3). There are less than 5% binucleated erythroblasts. The characteristic feature of the CDA I erythroblast is a spongy heterochromatin with a “Swiss cheese” appearance.80 Treatment includes interferon-α and iron chelation.5681

Image 

FIGURE 22-3 Erythrocyte precursors with nuclear bridging indicating dyserythropoiesis (bone marrow, ×1000). Source: (Modified from Rodak BF, Carr JH: Clinical hematology atlas, ed 4, St. Louis, 2013, Elsevier, Saunders.)

CDA II is the most common subtype and is inherited in an autosomal recessive pattern. More than 300 cases have been reported.81 It results from mutations in the SEC23B gene on chromosome 20.84SEC23Bencodes a component of the coat protein complex (COPII) that forms vesicles for transport of secretory proteins from the endoplasmic reticulum to the Golgi apparatus.85 Its exact role in the pathophysiology of CDA II is unknown. The anemia in CDA II is mild to moderate, with hemoglobins ranging from 9 g/dL to 12 g/dL and a mean hemoglobin of 11 g/dL.80 On peripheral blood film, RBCs are normocytic with anisocytosis, poikilocytosis, and basophilic stippling. The bone marrow has normoblastic erythropoiesis, with 10% to 35% binucleated forms and rare multinucleated forms.80 Occasional pseudo-Gaucher cells are also evident.80 Circulating RBCs hemolyze with the Ham acidified serum test but not with the sucrose hemolysis test.56 For this reason, CDA II is also known as HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum).56 The Ham test is no longer routinely used for CDA II confirmation, given the difficulty of appropriate quality control and the relative lack of testing availability in most laboratories.80 RBCs also agglutinate with anti antisera and show abnormal migration of band 3 using sodium dodecyl sulfate polyacrylamide gel electrophoresis.80 Treatment includes splenectomy and iron chelation.5681

CDA III is the least common of the CDA subtypes, with about 60 cases reported in the literature, the majority being from one Swedish family.86 This familial autosomal dominant form is associated with mutations in the KIF23 gene, which codes for a protein involved in cytokinesis.8687 The nonfamilial or sporadic form is extremely rare, with fewer than 20 cases reported.8186 The anemia is mild, and the hemoglobin is usually in the range of 8 to 14 g/dL, with a mean of 12 g/dL.80 RBCs are macrocytic, and poikilocytosis and basophilic stippling are evident. The bone marrow has megaloblastic changes, and giant erythroblasts with up to 12 nuclei are a characteristic feature. Patients rarely require RBC transfusions, and iron overload is not observed.

Myelophthisic anemia

Myelophthisic anemia is due to the infiltration of abnormal cells into the bone marrow and subsequent destruction and replacement of normal hematopoietic cells. Metastatic solid tumor cells (particularly from lung, breast, and prostate), leukemic cells, fibroblasts, and inflammatory cells (found in miliary tuberculosis and fungal infections) have been implicated.8889 Cytopenia results from the release of substances such as cytokines and growth factors that suppress hematopoiesis and destroy stem, progenitor, and stromal cells.89 With disruption of normal bone marrow architecture by the infiltrating cells, the marrow releases immature hematopoietic cells. Furthermore, because of the unfavorable bone marrow environment, stem and progenitor cells migrate to the spleen and liver and establish extramedullary hematopoietic sites.89Since blood cell production in the liver and spleen is inefficient, these extramedullary sites also release immature cells into the circulation.88

The severity of anemia is mild to moderate, with normocytic erythrocytes and reticulocytopenia. Peripheral blood findings include teardrop erythrocytes and nucleated RBCs, as well as immature myeloid cells and megakaryocyte fragments ().Figure 22-488 The infiltrating abnormal cells are detected in a bone marrow aspirate or biopsy specimen.

Image 

FIGURE 22-4 Myelophthisic anemia showing a leukoerythroblastic blood picture with a myelocyte, three orthochromic normoblasts, teardrop erythrocytes, a giant platelet with abnormal morphology, and a micromegakaryocyte (peripheral blood, ×1000).

Anemia of chronic kidney disease

Anemia is a common complication of chronic kidney disease (CKD), with a positive correlation between anemia and renal disease severity.9091 Coresh and colleagues reported that between 1999 and 2004, approximately 26 million adults over 20 years of age in the United States had CKD.92 The primary cause of anemia in CKD is inadequate renal production of erythropoietin.9091 Without erythropoietin, the bone marrow lacks adequate stimulation to produce RBCs. Another contributor to the anemia of CKD is uremia, which inhibits erythropoiesis and increases RBC fragility.9394 Furthermore, patients experience chronic blood loss and iron deficiency from hemodialysis and frequent blood draws. Chronic inflammation and a restricted diet may also limit the iron available for erythropoiesis.9091 Anemia of CKD is normocytic and normochromic with reticulocytopenia. Burr cells are common peripheral blood film findings in cases complicated by uremia.90

Anemia in CKD can lead to cardiovascular complications, kidney failure, and suboptimal quality of life.90 The Kidney Disease Outcomes Quality Initiative of the National Kidney Foundation recommends annual hemoglobin testing in patients with CKD and investigation of the anemia if the hemoglobin is less than 13.5 g/dL in adult men and less than 12 g/dL in adult women.90 Treatment includes recombinant human erythropoietin or other erythropoiesis-stimulating agents (ESAs), with a goal hemoglobin range of 11 g/dL to 12 g/dL.9095 Maintaining the hemoglobin above 13 g/dL is not recommended because of the increased risk of cardiovascular and thromboembolic complications.9095 Successful ESA therapy requires adequate iron stores, so plasma ferritin level and percent transferrin saturation should also be monitored. Iron is administered with ESA therapy to maintain the transferrin saturation above 20% and the plasma ferritin level above 100 ng/mL for non-dialysis-dependent patients and above 200 ng/mL for hemodialysis-dependent patients.90 Iron therapy is not routinely recommended for ferritin levels above 500 ng/mL.90

Patients may become hyporesponsive to ESA therapy because of functional iron deficiency (FID). In FID, the bone marrow is unable to release iron rapidly enough to accommodate the accelerated erythropoiesis. The transferrin saturation remains below 20%, but the serum ferritin level is normal or increased, indicating adequate iron stores.96 Patients with FID are unable to reach or maintain the target hemoglobin, even with high ESA doses. However, patients are able to reach the target hemoglobin after intravenous iron therapy.96 Researchers have proposed diagnostic criteria for FID in CKD: decreased reticulocyte hemoglobin content, increased soluble transferrin receptor, and greater than 10% hypochromic RBCs in the peripheral blood.9697 Other causes of ESA hyporesponsiveness include chronic inflammatory disease, infection, malignancy, aplastic anemia, antibody-mediated pure red cell aplasia, thalassemia, multiple myeloma, and the presence of hemoglobin H or hemoglobin S variants.90

Summary

• Bone marrow failure is the reduction or cessation of blood cell production affecting one or more cell lines. Pancytopenia (decreased RBCs, WBCs, and platelets) is a common finding. Sequelae of pancytopenia include weakness and fatigue, infections, and bleeding.

• Aplastic anemia may be acquired or inherited. Acquired aplastic anemia may be idiopathic or secondary to drugs, chemical exposures, radiation, or viruses. Acquired aplastic anemia may also occur with conditions such as paroxysmal nocturnal hemoglobinuria, autoimmune diseases, and pregnancy.

• Bone marrow failure in acquired aplastic anemia occurs from destruction of hematopoietic stem cells by direct toxic effects of a drug, autoimmune T-cell targeting of stem cells, or other unknown mechanisms. The autoimmune reactions are rare adverse events after exposure to drugs, chemicals, or viruses. They are idiosyncratic in that they are unpredictable, and severity is unrelated to the dose or duration of exposure.

• Aplastic anemia is classified as nonsevere, severe, or very severe, based on bone marrow hypocellularity, absolute neutrophil count, platelet count, hemoglobin level, and reticulocyte count (Table 22-1). The severity classification helps to guide treatment decisions.

• Preferred treatment for severe and very severe acquired aplastic anemia is hematopoietic stem cell transplant (HSCT) for younger patients with an HLA-identical sibling. For those without a matched sibling donor and for those who are not HSCT candidates, immunosuppressive therapy with antithymocyte globulin and cyclosporine is recommended.

• Fanconi anemia (FA), dyskeratosis congenita (DKC), and Shwachman-Bodian-Diamond syndrome (SBDS) are inherited forms of aplastic anemia with progressive bone marrow failure, and patients may present with characteristic physical malformations. FA is inherited in an autosomal recessive or X-linked pattern, and mutations in 15 genes have been identified. A positive chromosome breakage study with diepoxybutane is diagnostic. DKC can be X-linked, autosomal dominant, or autosomal recessive, and mutations in eight genes have been identified. SBDS is autosomal recessive and is associated with mutations in the SBDS gene.

• Telomerase complex defects play a role in the pathophysiology of inherited aplastic anemias and some acquired aplastic anemias. The defects result in the inability of telomerase to elongate telomeres at the ends of chromosomes, which leads to premature hematopoietic stem cell senescence and apoptosis.

• Pure red cell aplasia is a disorder of erythrocyte production. Acquired transient erythroblastopenia of childhood (TEC) and Diamond-Blackfan anemia (DBA) are disparate subtypes with distinct etiologies, clinical features, and courses (Table 22-4). Mutations in nine different ribosomal protein genes have been identified in DBA.

• Patients with congenital dyserythropoietic anemia (CDA) exhibit refractory anemia, reticulocytopenia, secondary hemosiderosis, and distinct abnormalities of erythroid precursors. Three major subtypes are recognized: CDA I, CDA II, and CDA III.

• Myelophthisic anemia results from the replacement of normal bone marrow with abnormal cells. The main cause of anemia of chronic kidney disease is inadequate production of erythropoietin by the kidneys.

Now that you have completed this chapter, go back and read again the case study at the beginning and respond to the questions presented.

Review questions

Answers can be found in the Appendix.

1. The clinical consequences of pancytopenia include:

a. Pallor and thrombosis

b. Kidney failure and fever

c. Fatigue, infection, and bleeding

d. Weakness, hemolysis, and infection

2. Idiopathic acquired aplastic anemia is due to a(n):

a. Drug reaction

b. Benzene exposure

c. Inherited mutation in stem cells

d. Unknown cause

3. The pathophysiologic mechanism in acquired idiosyncratic aplastic anemia is:

a. Replacement of bone marrow by abnormal cells

b. Destruction of stem cells by autoimmune T cells

c. Defective production of hematopoietic growth factors

d. Inability of bone marrow stroma to support stem cells

4. Based on the criteria in Table 22-1, what is the aplastic anemia classification of a 15-year-old female with a bone marrow cellularity of 10%, hemoglobin of 7 g/dL, absolute neutrophil count of 0.1 × 109/L, and platelet count of 10 × 109/L?

a. Nonsevere

b. Moderate

c. Severe

d. Very severe

5. The most consistent peripheral blood findings in severe aplastic anemia are:

a. Hairy cells, monocytopenia, and neutropenia

b. Macrocytosis, thrombocytopenia, and neutropenia

c. Blasts, immature granulocytes, and thrombocytopenia

d. Polychromasia, nucleated RBCs, and hypersegmented neutrophils

6. The treatment that has shown the best success rate in young patients with severe aplastic anemia is:

a. Immunosuppressive therapy

b. Long-term red blood cell and platelet transfusions

c. Administration of hematopoietic growth factors and androgens

d. Stem cell transplant with an HLA-identical sibling

7. The test that is most useful in differentiating FA from other causes of pancytopenia is:

a. Bone marrow biopsy

b. Ham acidified serum test

c. Diepoxybutane-induced chromosome breakage

d. Flow cytometric analysis of CD55 and CD59 cells

8. Mutations in genes that code for the telomerase complex may induce bone marrow failure by causing which one of the following?

a. Resistance of stem cells to normal apoptosis

b. Autoimmune reaction against telomeres in stem cells

c. Decreased production of hematopoietic growth factors

d. Premature death of hematopoietic stem cells

9. Diamond-Blackfan anemia differs from inherited aplastic anemia in that in the former:

a. Reticulocyte count is increased

b. Fetal hemoglobin is decreased

c. Only erythropoiesis is affected

d. Congenital malformations are absent

10. Which anemia should be suspected in a patient with refractory anemia, reticulocytopenia, hemosiderosis, and binucleated erythrocyte precursors in the bone marrow?

a. Fanconi anemia

b. Dyskeratosis congenita

c. Acquired aplastic anemia

d. Congenital dyserythropoietic anemia

11. The primary pathophysiologic mechanism of anemia associated with chronic kidney disease is:

a. Inadequate production of erythropoietin

b. Excessive hemolysis

c. Hematopoietic stem cell mutation

d. Toxic destruction of stem cells

References

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2.  Vaquez M.H, Aubertin C. L’anémie pernicieuse d’après les conceptions actuellesBull Soc Med Hop Paris; 1904; 21:288-297.

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*The authors acknowledge the contributions of Elaine M. Keohane, author of this chapter in the previous edition