A man presenting with nodules on hands and elbows.

Diagnosis: protothecosis. To determine the cause of the nodules on the patient’s hand (figure 1) and elbow (figure 2), culture of fluid obtained from the right olecranon bursa was performed and revealed Prototheca wickerhamii. A methylene blue wet mount revealed the characteristic sporangia with internal septations (figure 3). P. wickerhamii is an acrophyllic algae that is ubiquitous in nature. Prototheca have been isolated from tree sap, potato peels, and salt and fresh water (including seawater and water from marshes, ponds, streams, and lakes), as well as sewage and soil [1]. Human infection with this organism is very rare; most patients who are affected have impaired immunity [2, 3]. Human protothecosis most often manifests as cutaneous lesions and olecranon bursitis, but cases of pulmonary and hematogenous involvement have been described. Diagnosis can be made through culture of infected fluid in Sabouraud dextrose agar or by visualization of sporangia containing sporangiospores in histological cross-section. The treatment of protothecal infections is not standardized. The majority of isolates described have remained susceptible in vitro to amphotericin B and itra-