Role of Direct Immunofluorescence in Cutaneous Small-Vessel Vasculitis: Experience From a Tertiary Center.

Skin is commonly affected by vasculitic process and often subjected to biopsy. Cutaneous vasculitis can be either primary or part of a systemic vasculitic process. This study was conducted to evaluate the diagnostic utility of direct immunofluorescence (DIF) in determination of etiology of cutaneous vasculitis. All histologically proven cases of cutaneous vasculitis over the past two and half years were retrospectively analyzed along with their clinical and DIF findings (IgG, IgA, IgM, and C3). Within this study period, a total of 198 cases of small-vessel vasculitis were diagnosed based on skin biopsy and DIF findings. The mean age of patients was 31.2 years (range 1-84 years) with slight male dominance (M:F ratio 1.06:1). Henoch-Schonlein purpura/IgA vasculitis was the commonest clinical diagnosis (31%), followed by urticarial vasculitis (11%) and others. Idiopathic vasculitis was suspected in 33% cases. Overall, DIF was positive in 60% (119/198) cases, with vascular deposition of IgA being commonest, followed by C3. The clinical diagnosis of Henoch-Schonlein purpura could be confirmed in 61.5% (40/65) cases by DIF, whereas another 20 unsuspected cases were picked up as IgA vasculitis based on DIF findings. DIF findings confirmed lupus vasculitis in 50% cases. Other cases showed variable nonspecific deposition of C3 and IgM in 42% cases. DIF can be highly useful to classify cutaneous vasculitis, with maximum efficacy for diagnosis of IgA vasculitis and lupus vasculitis. It can aid in the accurate diagnosis even when the histological changes are minimal. All cases of suspected cutaneous vasculitis should be subjected to DIF.