Systemic Necrotizing Medium-Vessel Vasculitis Clinically Consistent With Polyarteritis Nodosa: A Detailed Case Report.

Polyarteritis nodosa (PAN) is a rare necrotizing vasculitis of medium-sized arteries presenting with heterogeneous multisystem involvement. Diagnosis is challenging due to the absence of specific biomarkers, frequent anti-neutrophil cytoplasmic antibodies (ANCA) negativity, variable early imaging findings, and low diagnostic yield of superficial biopsies. We report the case of a 33-year-old man experiencing a four-month evolution of recurrent inflammatory episodes involving abdominal, neurological, cutaneous, and cardiopulmonary systems. He developed dusky necrotizing vasculitic lesions, mononeuritis multiplex-type neuropathy, constitutional symptoms, markedly elevated inflammatory markers, and demonstrated a dramatic response to corticosteroid therapy. Computed tomography angiography was normal, and a superficial punch biopsy performed after steroid initiation was nondiagnostic, reflecting known limitations of sampling depth and timing. Despite this, clinical features, disease trajectory, exclusion of alternative vasculitides, and classical steroid responsiveness strongly supported systemic PAN. This case highlights the diagnostic limitations of biopsy and imaging in early PAN and emphasizes the need for clinical judgment and timely treatment.