Protothecosis: an unusual cause of chronic subcutaneous and soft tissue infection.

Protothecosis of subcutaneous and soft tissues is a rare occurrence in humans. We present two patients with chronic subcutaneous protothecosis affecting the elbow and foot respectively. Both patients had been treated with local corticosteroid injections and had recent exposure to water. The diagnosis was made histopathologically in both cases and confirmed by culture in one case. Histopathology showed typical Protothecal sporangia with surrounding mixed inflammatory infiltrate including necrotizing granulomas. Organisms stained positively with periodic acid-schiff, Gomori's methenamine silver, and Gridley fungus stains. In one case, intravenous chemotherapy was required to eliminate the pathogens. Histopathologic identification of the organisms is vital to ensure adequate therapy and avoid chronic smoldering infection.