Protothecosis is a rare cause of systemic and/or cutaneous infection. Because approximately 100 cases of human infection with Prototheca wickerhamii have been reported, little is known about the pathogenesis of this infection. Cases include both immunocompetent and immunocompromised patients. However, most cases contain an element of immune compromise, either local or systemic.
We present a case of an 81-year-old white woman with a history of multiple nonmelanoma skin cancers, including squamous and basal cell carcinomas and actinic keratoses, throughout her legs and thighs bilaterally. She presented to a central Florida dermatology clinic with complaints of persistent bumps on her right lower leg despite therapy with diclofenac sodium gel 3% and 5-fluorouracil cream 5%. Biopsies of skin specimens from the right lower leg revealed a dermal abscess that contained spherical funguslike organisms, with periodic acid-Schiff staining revealing 6- to 10-μm organisms with internal septations, which are characteristic of P wickerhamii.