Cutaneous Protothecosis Associated with Long-Term Topical Corticosteroid: Clinicopathological Diagnostic Pointers
Cutaneous protothecosis is a rare opportunistic infection caused by achlorophyllous algae of the genus Prototheca and often poses a diagnostic challenge because of marked clinical polymorphism and the absence of pathognomonic features. We report a case of cutaneous protothecosis in a 78-year-old woman with a long history of pruritic skin eruptions and a history of uncontrolled long-term use of topical corticosteroids. During prior evaluation, systemic connective tissue disease and a paraneoplastic etiology of the cutaneous process were excluded. The key diagnostic step was a skin biopsy with histopathological examination, which demonstrated a lichenoid pattern combined with productive granulomatous inflammation in the dermis, raising suspicion of an infectious dermatosis and prompting additional special stains. Ziehl–Neelsen staining was negative, excluding mycobacterial infection. Periodic acid–Schiff (PAS) staining revealed PAS-positive structures. Culture of shave-biopsy material on Sabouraud dextrose agar yielded Prototheca wickerhamii, confirming the diagnosis of protothecosis. The patient was started on itraconazole 100 mg twice daily, with gradual regression of skin lesions and improvement of subjective symptoms.