RESUMO
BACKGROUND: Histoid leprosy (HL) is a rare form of lepromatous leprosy, characterized by hyperchromic indurated nodules above normal skin. Its main histopathological aspect is spindle cells. Because it may simulate other aspects, such as dermatofibroma and neurofibroma, histoid leprosy poses itself as a diagnostic challenge. METHODS: This is a retrospective study with all patients having been selected from the leprosy clinic of the Hospital das Clínicas da Universidade de São Paulo from 2006 to 2016. RESULTS: There were 12 patients in this study, eight in the histoid group and four in the lepromatous leprosy group. The prevalence of HL was 1.12% in all leprosy subjects. All individuals from HL group were "de novo" cases, and the histopathological analysis of skin lesions presented spindle cells generating a storiform pattern. Immunohistochemistry for CD68, vimentin, and anti-BCG were positive in all 12 cases. Factor XIIIa was visualized only in the papillary dermis, and S100 protein was negative in all biopsies. Smooth-muscle actin was present in 62.5% of the HL samples. CONCLUSION: The prevalence of HL was similar to previous reports. However, all histoid patients were "de novo" cases, differing from published studies. Fusocellular macrophage transformation could be explained by the differences in cytoskeleton proteins expressed in histoid lesions in comparison to other leprosy variants, with emphasis on vimentin and smooth muscle actin.
