Role of s-100 immunostaining in demonstration of nerve changes and quantification of dendritic cells in leprosy.

Background: A definitive diagnosis of leprosy is based on a demonstration of either acid-fast bacilli or nerve elements within the granulomas. On routine hematoxylin and eosin stains, the nerve fibers are not easily identifiable. In this study, S-100 immunostain is used to highlight the nerve elements and to demonstrate and compare the nerve changes in spectrum of leprosy including reactions. Aim: To demonstrate the nerve changes in spectrum of leprosy using S-100 immunostaining so as to categorize them for the purpose of early diagnosis and treatment. We also want to demonstrate and quantify the dendritic cells in lepromatous spectrum of leprosy using S-100 immunostain. Materials and Methods: Twenty consecutive skin biopsy specimens from patients with histopathological diagnosis of leprosy in the year 2012 were studied. Of these 20 cases, 13 were Borderline Tuberculoid, 1 was of indeterminate leprosy, 1 Borderline Lepromatous, 2 cases of Lepromatous Lep-rosy , 1 case of Type 1 reac-tion and 2 cases of Type 2 reaction. Stains used were Hematoxylin and Eosin stain for the histopathological diagnosis, Fites stain for Bacillary index and S-100 immunoperoxidase staining for nerve changes. 5 cases of granulomatous dermatosis of skin other than leprosy (5 cases of lupus vulgaris) were included as controls. Results: On Hematoxylin and Eosin staining, the nerve fibers showed vertical orientation in relation to epidermis in Borderline Tuberculoid leprosy. In addition , the nerve fibers showed rounded contour in Tuberculoid leprosy. The entire spectrum of leprosy showed evidence of nerve damage in S-100 immunostaining which was categorized in 4 patterns 1. Absent, 2. Fragmented, 3. Discontinuous and 4. Intact. The majority of Borderline Tuberculoid leprosy cases showed absent pattern of nerve damage. Dendritic cells were also positive for S-100 immunostaining with granular positivity in Borderline Tuberculoid Leprosy cases and membranous positivity in Lepromatous spectrum. Conclusion: Nerve damage is seen across the entire spectrum of leprosy and the early identification of this nerve damage using S-100 immunostaining, helps to differentiate between Lepromatous and Tuberculoid leprosy, especially in the borderline and indeterminate forms.