Abstract
Cutaneous protothecosis is a rare opportunistic infection caused by achlorophyllous algae of the Prototheca genus, presenting a diagnostic challenge due to its clinical polymorphism and lack of pathognomonic features.
We report a case of cutaneous protothecosis in a 78-year-old female patient with a long history of pruritic skin eruptions and 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 definitive diagnostic step was a skin biopsy with histopathological examination, which revealed a lichenoid reaction along with productive dermal granulomatous inflammation, raising suspicion of an infectious origin of the dermatosis and prompting additional special stains. Ziehl–Neelsen staining was negative, and no acid-fast mycobacteria were identified. Periodic Acid–Schiff (PAS) staining revealed PAS-positive structures. Culturing of shave-biopsy material on Sabouraud dextrose agar yielded Prototheca wickerhamii, confirming the diagnosis of protothecosis. The patient was started on itraconazole, resulting in gradual regression of skin lesions and improvement of subjective symptoms.