Tissue eosinophilia as an indicator of drug-induced cutaneous small-vessel vasculitis

Objective: To determine whether tissue eosinophilia is a reliable indicator of a drug-induced etiology in biopsy samples demonstrating leukocytoclastic vasculitis. Design: Retrospective medical record review with concurrent histopathologic analysis. Setting: University-affiliated dermatology practice. Patients: Sixty-three patients with cutaneous small-vessel vasculitis meeting specific inclusion criteria were divided into drug-induced (n = 16) and non - drug-induced (n = 47) groups. Main Outcome Measures: Corresponding histopathologic material was reviewed by a dermatopathologist masked to the etiologic associations. An eosinophil ratio was calculated for each patient, derived from the mean eosinophil score ( averaging eosinophil counts from 10 high-power histologic fields), and expressed in relation to the intensity of inflammation in the histopathologic slides examined. Eosinophilia ratios were compared for both groups using the Mann-Whitney test. Results: A significant difference was found in mean eosinophil ratios in the drug-induced vs non - drug-induced groups (5.20 vs 1.05; P =. 01). Vascular fibrin deposition was present in both groups and was not found to be significantly different (P =. 78). Clinical evidence of systemic vasculitis was present in 2 patients (13%) in the drug-induced group vs 15 (32%) in the non - drug-induced group. Fourteen patients (88%) in the drug-induced group had a short-term disease course vs 27 (57%) in the non - drug-induced group. Conclusions: Tissue eosinophilia is established as a reliable indicator of drug induction in cutaneous small vessel vasculitis. Drug-induced small-vessel vasculitis generally follows a short-term disease course without development of systemic involvement. This information may be useful for guiding management decisions, especially when the etiology is unclear.