The histopathologic spectrum of erythema induratum of Bazin.

Erythema induratum of Bazin is a tuberculid that is strongly associated with tuberculosis. Clinically, erythema induratum of Bazin show recurrent tender subcutaneous nodules that occur mainly on the calves of women with tuberculin hypersensitivity. Previous studies have not documented the histopathologic spectrum of erythema induratum of Bazin in detail. We identified two major histopathologic groups in 19 of 20 skin biopsies obtained from 20 patients with well-documented erythema induratum of Bazin. Six cases (group I) showed focal septolobular panniculitis in close association with a single muscular artery or small vessel with primary neutrophilic vasculitis. Thirteen cases (group II) revealed diffuse septolobular panniculitis with primary neutrophilic vasculitis of either large or smaller vessels. Both groups showed varying combinations and degrees of acute and chronic inflammation, coagulative and caseation-like necrosis, and granulomatous inflammation. Poorly developed granulomas predominated, but mixed, palisading, and lipophagic granulomas also occurred. Inflammation and necrosis were more extensive in group II. Erythema induratum of Bazin may show predominantly acute suppurative or granulomatous panniculitis. Immunostaining showed S100+ antigen-presenting cells, macrophages, and T-lymphocytes. B-lymphocytes were rare. The presence of primary vasculitis and granulomas suggests that types III and IV hypersensitivity reactions play a role in the pathogenesis or erythema induratum of Bazin. The latter remains a clinicopathologic diagnosis, but awareness of the heterogeneous histopathologic spectrum of EIB will ensure a timely diagnosis and institution of antituberculous treatment.