Lepromatous reaction mimicking a primary systemic vasculitis: Case report and literature review.

Lucio's phenomenon is a rare necrotizing skin reaction, almost exclusive to diffuse lepromatous leprosy, that can mimic systemic vasculitis and lead to diagnostic and therapeutic errors. We report the case of a 32-year-old woman from Paraguay with prolonged fever, hepatomegaly, and violaceous, painless necrotic skin lesions on her limbs. She was initially treated with corticosteroids for presumed vasculitis without clinical improvement. Physical examination revealed madarosis, lepromas, and altered thermal-pain sensitivity. Skin biopsy showed a perivascular histiocytic infiltrate with acid-fast bacilli, confirming multibacillary lepromatous leprosy. Treatment with rifampicin, dapsone, and clofazimine was initiated, resulting in good clinical evolution. Lucio's phenomenon is an immune-mediated vasculopathy that may produce false-positive serologies and mimic autoimmune diseases. Histopathological confirmation is essential to avoid unnecessary immunosuppressive therapy. It should be considered in the differential diagnosis of necrotic skin ulcers, especially in patients from endemic regions. Early recognition and specific treatment help prevent severe complications.