Systemic Idiopathic Polyarteritis Nodosa Mimicking Cryoglobulinemic Vasculitis: A Diagnostic Challenge.

Polyarteritis nodosa (PAN) is an uncommon systemic vasculitis involving predominantly medium-sized arteries. Its heterogeneous presentation and relapsing-remitting course often lead to diagnostic delay. We report a 68-year-old male with a 15-month history of progressive peripheral neuropathy, recurrent vasculitic rash, renal impairment, and testicular pain. Laboratory investigations revealed elevated inflammatory markers, positive rheumatoid factor, type II cryoglobulins, and negative antineutrophil cytoplasmic antibody (ANCA). Complement levels were normal on repeated testing, and urinalysis showed isolated proteinuria without red blood cells or casts, arguing against other differentials like cryoglobulinemic vasculitis and glomerulonephritis. Skin biopsy demonstrated leukocytoclastic vasculitis. After excluding secondary causes, including hepatitis B, ANCA-associated vasculitis (granulomatosis with polyangiitis and microscopic polyangiitis), IgA vasculitis, and cryoglobulinemic vasculitis, a diagnosis of systemic idiopathic PAN was established. Cyclophosphamide was considered but avoided due to pre-existing renal impairment. The patient was treated with high-dose prednisolone for induction, followed by low-dose azathioprine as a steroid-sparing agent, with subsequent clinical improvement. This case illustrates the diagnostic difficulty of distinguishing PAN from cryoglobulinemic vasculitis when overlapping serological features are present, and the consequences of delayed recognition on organ function.