Role of S100 immunostaining in demonstrating neural granulomas in paucibacillary leprosy

Abstract

Background: Challenges encountered in diagnosing paucibacillary leprosy are difficulty in visualizing the nerve twigs in H&E section due to small size or fragmentation and paucity of organisms in Wade-fite stain. Aims: This study aims to test the role of S100 immunostain in demonstration of neural granuloma, the hallmark in paucibacillary leprosy, compare morphology of S100 staining of nerves inside granuloma in different types of leprosy and distinguish this pattern from non-leprosy cutaneous granulomas. Methods: Sixty cases of diagnosed paucibacillary leprosy were studied in a span of one and half year (January 2018 to June 2019). Ten cases of non-lepromatous cutaneous granulomas and five cases of normal skin histology were also studied and included as control. H&E stain along with S100 immunostaining was done for all the cases. The H&E stained slides were used for studying the histopathological features and the S-100 was used for identifying the different dermal nerve patterns. Results: The most common pattern seen in case of borderline tuberculoid was fragmented and infiltrated whereas most common pattern seen in case of indeterminate was intact and infiltrated. Reduced, fragmented and infiltrated was most commonly seen in case of tuberculoid leprosy. Conclusion: Immunohistochemistry with S-100 has shown to be an effective adjuvant to histopathology in the diagnosis of different types of paucibacillary leprosy with bacterial index zero and to differentiate them from non-lepromatous granulomatous condition.