Role of S-100 Immunostaining in Differentiation of Borderline Leprosy from Other Granulomatous Diseases of Skin

ABSTRACT

Leprosy is a chronic granulomatous disease affecting skin, peripheral nerves and other tissues. On histopathology leprosy mimics other infectious and non-infectious lesions like tuberculosis, sarcoidosis and fungal infections, which are also common in our country. In tuberculoid and indeterminate forms, where Acid Fast Bacilli cannot be demonstrated, the diagnosis becomes more difficult. Mycobacterium leprae is the only bacterium which has the ability to infiltrate peripheral nerves leading to Schwann cell disintegration. On routine Hematoxylin and Eosin stains (H&E), the nerve fibers may not be easily identifiable in some cases , hence S-100 immunostaining is used to highlight the nerve elements and to demonstrate and compare the nerve changes in spectrum of leprosy. With widespread use of multi-drug treatment, there has been changes in the profile of disease. The aim of the present study was to observe different patterns of cutaneous nerve involvement in leprosy and to correlate these with the clinical and histopathological findings in currently referred cases for histopathological opinion. The study was conducted in the Department of Pathology, Himalayan Institute of Medical Sciences, Swami Rama Himalayan University, Dehradun, over a period of 12 months (July 2016 - July 2017) Subjects were recruited from patients presenting in Dermatology OPD. A total 35 consecutive cases with clinical suspicion / diagnosis of leprosy were included in the study. Biopsies were processed and stained by H&E, Fite-Faraco as well as S100 immunostaining. It was observed that on S-100 immunostaining, 43.7% cases showed granulomas infiltrating the dermal nerves whereas these changes could not be demonstrated in 16.6% cases of Borderline leprosy on H&E staining alone. Thus S-100 staining appears to serve as an important tool to diagnose leprosy from other granulomatous diseases of skin even in current scenario of leprosy.