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Case Reports

Abstract

A 75-year-old man was admitted to the ICU for progressive weakness, shock, gastrointestinal bleeding, and acute kidney injury. He had recently received minocycline for Nocardia-positive bronchoalveolar lavage following pneumonia. Examination revealed retiform purpura over the right upper extremity and flank, concerning for vasculitis. Punch biopsy demonstrated florid small-medium vessel vasculitis spanning the dermis to superficial subcutis with extensive deep fibrin thrombi, epidermal and eccrine ischemia, leukocytoclasia, and abundant neutrophilic inflammation. Special stains were negative for microorganisms. Subsequent renal biopsy revealed acute necrotizing arteritis with necrotizing crescentic glomerulonephritis. Imaging showed cavitary lung lesions and myonecrosis; colonoscopy demonstrated irregular mucosal ulcerations. Serology was positive for myeloperoxidase (MPO) antibodies and p-ANCA, confirming MPO+ ANCA-associated vasculitis. The patient was treated with glucocorticoids, rituximab, and avacopan. Given the systemic and laboratory findings, the overall picture is classic for ANCA-associated vasculitis, particularly microscopic polyangiitis (MPA). MPA is a primary systemic small-to-medium-vessel vasculitis with dermatologic, renal, pulmonary, gastrointestinal, neurologic, and rarely myopathic manifestations. Drugs such as minocycline are implicated in its development. The dermatopathologic differential includes IgA vasculitis, which shows less thrombosis, and septic vasculitis, which demonstrates less neutrophilic inflammation and leukocytoclasia. MPA is distinguished from other ANCA-associated vasculitides by the absence of granulomatous inflammation or eosinophilia. This case highlights the value of skin biopsy in diagnosing systemic vasculitis, the importance of clinicopathologic correlation in differentiating MPA from other vasculitides, and the need to consider recent drug exposure as a potential trigger. Prompt recognition of minocycline-induced MPA is critical to initiate therapy and prevent irreversible organ damage.