Recurrent Lower-Extremity Purpura Mistaken for Cellulitis: Hepatitis C Virus-Associated Type III Mixed Cryoglobulinemic Vasculitis.

Mixed cryoglobulinemia is a small-vessel vasculitis mediated by cold-precipitable immune complexes, and chronic hepatitis C virus (HCV) infection is its most common cause. Cutaneous disease, classically palpable purpura of the lower limbs, is the most frequent manifestation but is readily mistaken for cellulitis or other dermatoses, delaying diagnosis. We describe a 61-year-old woman with chronic HCV, a long smoking history, and active cocaine use who experienced more than a year of recurrent, painful, pruritic erythematous - purpuric eruptions of the lower extremities that were repeatedly treated empirically as cellulitis without benefit. She also reported new easy bruising and skin fragility. Inflammatory markers were elevated, an extended antinuclear antibody panel was negative, and serum cryoglobulins were positive; immunofixation of the cryoprecipitate demonstrated type III (polyclonal) mixed cryoglobulinemia. Urinalysis showed hematuria with low-grade proteinuria, indicating renal involvement, and complement C4 was at the low end of normal. The findings established HCV-associated type III mixed cryoglobulinemic vasculitis. Cocaine history required consideration of levamisole-adulterated cocaine vasculopathy, an important mimic. She was started on corticosteroids with rheumatology co-management and HCV-directed direct-acting antiviral therapy as the cornerstone of treatment. Following completion of antiviral therapy and achievement of sustained virologic response, cutaneous vasculitis resolved, urinalysis normalized with no evidence of active glomerulonephritis, and the corticosteroid dose was successfully tapered. The patient remains on prednisone 5 mg daily with ongoing taper. This case underscores cryoglobulinemic vasculitis as a cause of recurrent, cellulitis-like, lower limb eruptions, and the primacy of antiviral cure in achieving vasculitis remission.