Primary cutaneous aspergillosis mimicking dermatophytosis

We recently reviewed a skin biopsy specimen obtained from a child with acute monocytic leukemia that demonstrated abundant mycelia present within a keratin plug of a hair follicle, a granulomatous dermal inflammatory infiltrate, and focal dermal invasion by fungi. These histologic findings were suggestive of an invasive dermatophyte infection; however, Aspergillus flavus was identified by culture. This case illustrates the need for care in interpreting biopsy specimens of cutaneous fungal infection in the immunocompromised host, since proper treatment is determined by the specific agent present. The morphological features of fungi in tissue sections and histopathologic patterns of host response in the immunocompromised patient may be misleading in trying to identify fungal pathogens. At present, culture is the most reliable method for identifying pathogenic fungi and should be utilized to confirm appropriate therapy.