Prototheca, a genus of achlorophyllic algae, is a rare cause of opportunistic infection in humans. About 80 human cases, mostly cutaneous infection caused by P. wickerhamii, have been reported world-wide. We describe the clinicopathological findings and treatments of five cases diagnosed in our department during the period 1991-97. The patients, including four elderly farmers, presented with pyoderma-like lesions or infiltrating papules and plaques on the extensor side of the extremities or face. All patients were immunocompromised, mostly due to systemic or topical steroids. The diagnosis was made in each case by finding typical endospores with morula-like structures in skin biopsy specimens. P. wickerhamii was isolated in four cases in which pretreatment culture of skin tissue was done. Except for one patient who died of asthma, the infection was cured after 2-7 weeks of amphotericin B, ketoconazole, itraconazole or fluconazole. Our cases illustrate that cutaneous protothecosis commonly manifested non-tender, pyoderma-like or infiltrating lesions and should be considered in the differential diagnosis of deep fungal or mycobacterial infection. This rare infection seemed more frequent in our region, possibly due in part to common steroid abuse among old people in Taiwan and there was a large population of elderly farmers in our area.
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