Erythema multiforme in leprosy

The clinical course of leprosy is often interrupted by reactions, which are acute inflammatory episodes that can be classified as type I or type II. Type II reactions can present as cutaneous lesions that resemble erythema multiforme (EM). EM is classically associated with drug allergies or pre-existing viral infections. However, the differential diagnostic criteria of the diverse causative agents remain controversial. The aim of this study was to determine both the clinical relevance and the morphological and immunohistochemical characteristics of the EM-like lesions during the course of type II leprosy reactions. Twenty-seven skin biopsies were taken from typical EM-like lesions of multibacillary patients and reviewed; their histological features were correlated to their clinical aspects. Then, a computer-assisted morphometric analysis was performed to measure the extent of angiogenesis during these acute episodes. The histopathological and immunohistochemical analysis of the EM lesions revealed that they shared the same features that have been previously described for ENL, including immunopositivity in the identical cell-mediated immune markers. Our results point to leprosy as the cause of the EM-like lesions in our patients. Therefore, leprosy should be considered in the differential diagnosis of EM.