Histopathological examination of skin biopsies from an epidemiological study of leprosy in northern Malawi.

This report describes the histopathological findings in 686 biopsies obtained from 664 individuals during the course of a total population survey for leprosy in Northern Malawi. The criteria for the selection of cases for biopsy, the biopsy technique using a 4-mm punch, fixation method, transport of biopsies from Africa to the United Kingdom, and the method of coding histopathological results are described. Fifty-two percent (354) of the biopsies showed definite evidence of leprosy on histopathological examination. Using the Ridley-Jopling system, these biopsies were classified as follows: TT = 60 (17%); TT/BT = 68 (19%); BT = 194 (55%); BT/BB = 4 (1%); BB = 4 (1%); BB/BL = 4 (1%); BL = 7 (2%); BL/LL = 3 (1%); LL = 6 (2%). In addition, four (1%) biopsies were classified as "indeterminate" on histology, meaning that although there was evidence of leprosy it was not possible to provide a precise classification. A further 117 biopsies (17% of the total) had abnormal changes, often including epithelioid cell granulomas, possibly caused by leprosy but lacking specific criteria for that diagnosis. Finally, 203 (30%) of the biopsies had nonspecific (often minimal) changes, and 11 (2%) of the total showed evidence of some dermatological condition other than leprosy. Histopathological examination of biopsies in this study confirmed the clinical classification in 98% of the cases in which the histopathologist found evidence of leprosy, and supplied further evidence for the very high proportion of paucibacillary cases in this part of the world.