BACKGROUND: Primary neuritic leprosy (PNL) is a rare form of leprosy where the characteristic skin lesions are absent. Investigations of apparently normal skin from the areas of sensory change have revealed microscopic evidence of nerve involvement. Clinical studies have found that a proportion of patients develop visible skin lesions during follow-up. The aim of the study was to perform a clinical and histological analysis of PNL patients who developed visible skin lesions during treatment and follow-up, to gain insight into the pathogenesis of the disease.
METHODS: Twenty-nine individuals in a series of 182 PNL patients developed visible skin lesions during follow-up. Analysis of the number, location, histology and time of onset of the new skin lesions in relation to the type and regularity of the treatment regimen were noted. A biopsy from the new skin lesion when available was compared with the nerve biopsy findings at the time of initial diagnosis.
RESULTS: Thirty-eight per cent of patients developed a single patch and 28% developed two patches. Over three-quarters of these were on the lower limb (47%) or the upper limb (29%). Sixty-two per cent of patients developed the lesions within 2 years of the onset of symptoms. Patients on regular treatment developed patches earlier than those on irregular treatment or no treatment. A skin biopsy from the new patch revealed borderline tuberculoid leprosy histology in 47% of the patients.
CONCLUSIONS: The findings suggest that leprosy primarily affects the nerve and that a neuritic phase precedes the development of visible cutaneous lesions.
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