S-100-protein-positive dendritic cells in nodular vasculitis

Histopathologic features of erythema nodosum--like lesions in Behçet disease: a comparison with erythema nodosum focusing on the role of vasculitis

Many patients with Behçet disease (BD) develop lesions that clinically resemble those of erythema nodosum (EN) but differ from that condition with regard to their microscopic features. We examined 11 sections of EN-like lesions in BD and compared them with 9 sections of classic EN using routine histopathology and immunohistochemistry so as to form a comprehensive picture of the pathologic findings in BD and to determine the role of vasculitis in the formation of lesions. Erythema nodosum-like lesions of BD are characterized by panniculitis, usually lobular or mixed septal and lobular in pattern, with variable numbers of neutrophils, lymphocytes, and histiocytes as well as variable numbers of necrotic adipocytes. Vasculitis was noted in most EN-like lesions in BD. Scattered vessels showing lymphocytic vasculitis were evident in 6 sections, and foci of leukocytoclastic vasculitis were obvious in 4 sections, sometimes with phlebitis or arteriolitis. In specimens with classic EN, we did not observe vasculitis. Only the percentages of CD3+ lymphocytes and chloroacetate esterase-positive neutrophils in the infiltrating cells showed statistically significant differences (P < 0.05) between EN-like lesions in BD and EN through immunohistochemical and enzyme cytochemical studies. Because vasculitis in the EN-like lesions in BD was extensive and not limited to areas of severe inflammation, we believe that it is primary vasculitis. We suggest that vasculitis is an important pathologic event in EN-like lesions in BD but cannot determine the extent to which other pathologic changes such as septal or lobular panniculitis, fat necrosis, neutrophilic infiltration, or microabscess formation are secondary features.

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.