The pathogenesis and classification of polar tuberculoid leprosy

Abstract

Skin biopsies received from about 1,500 patients of varied ethnic and geographical origins produced 26 cases that fell within the polar tuberculoid (TT) group on the strictest definition, and a further 18 cases that might be considered as TT on histological and immunological grounds. The 44 cases were of 2 broad types. Nearly half were characterized by many lymphocytes but few other histological features, with no severe nerve involvement, no signs of reaction and good clinical-histological correlation. The remainder were characterized by severe nerve involvement or erosion of the epidermis and often by signs of reaction, all of which are associated with high lymphocyte transformation values; many of these cases were clinically BT. There was a fairly sharp distinction between these 2 types, with an intermixing of features only in cases that were not truly polar. There was also a partial geographical separation of the 2 types. The first appeared to represent primary lesions with high cell-mediated immunity; the second to have evolved through reactions associated with delayed hypersensitivity.