Histoplasmosis in the olecranon bursa of a patient with idiopathic CD4 lymphocytopenia.

摘要

Idiopathic CD4 lymphocytopenia (ICL) is a rare, non-human immunodeficiency virus (HIV)-related syndrome with a decrease in absolute CD4 T-lymphocyte counts to less than 300/mm3 or less than 20% of total T cells on more than 2 occasions at least 6 weeks apart. It was first defined in 1992 and later summarized in an updated review in the New England Journal of Medicine in 1993.' The absence of any other primary or secondary immunodeficiency causing a low CD4 T-cell count is also a requirement for diagnosis. This heterogeneous syndrome is most likely due to genetics and unrelated to HIV-1, HIV-2, human T-lymphotrophic virus, or other transmissible agents. It typically presents in adulthood, appears to have no sex predilection, and may be associated with autoimmunity. The pathogenesis of this syndrome is a decrease in the generation of T-cell precursors, abnormal T-cell apoptosis, biochemical failure of CD3 T-cell receptor, and defective cytokine production causing depressed T-cell immunity. It can be differentiated from HIV based on the slow rate of decrease in CD4 cell counts and the lack of a compensatory increase in CD8 cell counts and immunoglobulin. Although clinical findings depend on the degree of immune suppression, these patients are often predisposed to opportunistic infections. A cohort study of 47 ICL patients showed that pulmonary and extrapulmonary cryptococcal, mycobaeterial, pneumocystis, can-didal, and cytomegaloviral infections were commonly seen in these individuals. Cryptococcal meningitis is one of the most commonly described infections in the literature, but rare cases of progressive multifocal leukoencephalopathy and lymphoproliferative diseases have been reported. Patients with ICL are also susceptible to fungal infections with Histoplasma capsulatum.