Definition
• Opportunistic infections affecting the heart in immunocompromised patients
Pathogenesis
• In an immunocompromised individual (e.g., after transplantation or chemotherapy or in those with AIDS), organisms with low virulence can infect the heart
Clinical features
Epidemiology
• Most immunocompromised patients develop bacterial, fungal, or viral infections in the lung, gastrointestinal tract, skin, and the nervous system. The heart is only rarely involved
• Organisms commonly infecting the heart include Toxoplasma, cytomegalovirus (CMV), fungi (Candida, Aspergillus, and Mucor), and parvovirus B19
Presentation
• Fever, shortness of breath, chest pain, tachycardia. Patients may need ventilatory or circulatory support. Elevated cardiac enzymes and rising antibody titers might be detected in patients with viral myocarditis
• In addition, patients may present with unexplained neurological or pulmonary symptoms related to lesions at other sites
• Advanced cases may only be detected at the time of autopsy
Prognosis and treatment
• Depends on early identification and classification of the potential pathogen
• The incidence of opportunistic infections is declining in AIDS patients with the onset of highly active antiretroviral therapy therapy and better chemoprophylaxis
Pathology
Histology
• Multifocal areas of myocyte necrosis and acute inflammation are generally noted in fungal infections probably due to angioinvasion
• Granulomatous lesions may be seen with histoplasmosis, blastomycosis, and coccidioidomycosis
• In toxoplasmosis, there is lymphocytic myocarditis with intracystic bradyzoites in the myocytes on a background of intramural and perivascular fibrosis. Cysts may be also seen in normal-appearing myocardium
• In viral myocarditis, serological analysis might be useful. Parvovirus B19 infection of the endothelium may lead to endothelial dysfunction and may mimic acute coronary insufficiency in the absence of coronary disease
Immunopathology/special stains
• PAS and GMS stains are useful in identifying fungal hyphae and cysts
• Immunohistochemical stains can be performed to aid the diagnosis of toxoplasma, CMV, and parvovirus infections
Main differential diagnoses
• Cardiac allograft rejection (transplant setting): clinical history, C4d staining
• Drug-induced myocarditis
Fig 1 Opportunistic cardiac infections. H&E stained section of myocardium showing numerous, refractile, nonseptate, broad, hyphal forms of Mucor within an intravascular cellular thrombus. Adjoining myocytes show mild hypertrophy.
Fig 2 Opportunistic cardiac infections. H&E stained section of myocardium with focus of myocyte necrosis and abscess formation. Note Mucor hyphae in blood vessel.
Fig 3 Opportunistic cardiac infections. H&E stained section, at a higher magnification, shows dead myocyte fibers, acute inflammatory exudate, and multiple fragments of refractile, broad, hyphal forms of Mucor species.
Fig 4 Opportunistic cardiac infections. C4d staining shows no endothelial/vascular staining. The nonviable and dead myocyte fibers show strong cytoplasmic immunoreactivity for C4d.
Fig 5 Opportunistic cardiac infections. H&E stained section of myocardium with numerous intracystic bradyzoites of Toxoplasma. Note the lack of inflammatory response in this case.
Fig 6 Opportunistic cardiac infections. Immunostaining for Toxoplasma gondii weakly stains the intracytoplasmic bradyzoite forms of the organism. Note that lipofuscin within uninfected myocytes appears brown and should not be mistaken for organisms.