Histological changes in the nerve, skin and nasal mucosa of patients with primary neuritic leprosy.

Primary neuritic leprosy (PNL) presents as a peripheral neuropathy with no visible skin patches and skin smears negative for acid fast bacilli. The pathogenesis of PNL is poorly understood. The aim of the study was to document the histological changes in the nerve, apparently normal skin and nasal mucosa in PNL and to study its significance to the pathogenesis of leprosy lesions. The study is based on a cohort of 208 PNL patients registered at the Schieffelin Leprosy Research and Training Centre, Karigiri. All patients had a nerve biopsy, 196 had a skin biopsy and 39 had a nasal mucosal biopsy. The findings reveal that PNL patients exhibit a spectrum of disease histologically in the nerve ranging from lepromatous to tuberculoid leprosy with a significant proportion (46%) manifesting a multibacillary leprosy histology. Findings in the apparently normal skin and nasal mucosa reveal that there are widespread changes due to leprosy in tissues such as the skin and nasal mucosa even when the disease appears clinically confined to a few nerves. PNL may be an early stage in the pathogenesis of the disease before the appearance of skin lesions. The number of nerves enlarged and lepromin status did not give any clue to the nature of underlying disease.