Most skin eruptions and rashes are more or less pruritic, but there are states where there is severe pruritus in the absence of skin lesions, except for scratch marks (Fig. 35-1). This is called pruritus sine materia (from Latin, “itch without physical substrate”).
The diagnostic approach to the patient with generalized pruritus without identifiable skin lesions is a diagnosis of exclusion.
Pruritus is a symptom of skin disease that at the time of examination does not manifest with specific lesions.
It may be due to an internal organ disease, metabolic and endocrine conditions, or hematologic disease.
It may be a manifestation of malignant tumors, psychogenic states, or HIV infection; or it may be related to injected or ingested drugs.
The various causes of pruritus sine materia are listed in Table 35-1, and an algorithm of how to approach a patient with pruritus sine materia is shown in Table 35-2.
Skin signs may be clinically inapparent, perhaps confined to only circumscribed areas, and this is particularly important with regard to the exclusion of scabies, pediculosis, or conditions such as urticaria factitia.
Figure 35-1. Pruritus without diagnostic skin lesions This patient had multiple scratch marks due to compulsive scratching because of severe pruritus. There were no other diagnostic lesions. Workup revealed biliary cirrhosis without jaundice.
TABLE 35-1 CAUSES OF PRURITUS SINE MATERIA
TABLE 35-2 APPROACH TO THE DIAGNOSIS OF GENERALIZED PRURITUS WITHOUT DIAGNOSTIC SKIN LESIONS
Most Important Causes (See Table 35-1)
1. Identify and treat underlying disease.
2. Treat xerosis with baths and emollients.
3. UVB and narrow-band (311 nm) phototherapy or PUVA (in renal-, biliary-, aquagenic-, and polycythemia vera–related pruritus).
4. Topical agents: capsaicin, doxepin 5%, camphor/menthol, topical 3% aspirin solution (helps with lichen simplex chronicus (LSC)), pramoxine, naltrexone cream 1%.
5. Oral agents: Naloxone, naltrexone (25-50 mg/d), or ondansetron; antihistamines, tricyclic antidepressants (decrease central itch perception), thalidomide (especially in HIV), low-dose gabapentin (start at 300 mg/d but may need to titrate up as high 2400 mg/d before deemed ineffective); cholestyramine in cholestatic itch (but ineffective in total biliary obstruction).
Figure 35-2. Notalgia paresthetica This condition in the interscapular region is characterized by intense pruritus without skin lesions. The erythema seen here is due to rubbing and scratching.