: Leprosy is one of chronic granulomatous disease that is caused by Mycobacterium leprae. This bacillus has a high affinity for skin and peripheral nerve cells. In multibacillary (lepromatous leprosy) cases, the demonstration of acid fast bacilli usually concludes the diagnosis, which is not the case with paucibacillary (tuberculoid leprosy) cases. The diagnosis of tuberculoid leprosy is often difficult as most of the cases do not show acid fastness with 5% H2
and hematoxylin and eosin (H&E) stain also fails to demonstrate nerve involvement in granulomas. This study evaluates the utility of S-100 staining in identifying nerve fragmentation and differentiation of tuberculoid leprosy from other cutaneous granulomatous diseases.
Aim: To study various pattern of nerve involvement in leprosy by S-100 and to calculate and compare sensitivity of S-100 and H&E stain in nerve demonstration in tuberculoid cases and overall.
Methods: Thirty (30) adequate skin biopsies with a clinical and histopathological diagnosis of leprosy were taken. Out of these 30 cases, 12 cases had borderline tuberculoid leprosy, 7 had borderline lepromatous, 4 were of lepromatous leprosy. Tuberculoid, indeterminate and midborderline leprosy constituted 3, 3 and 1 case respectively. 10 cases of granulomatous dermatosis of skin other than leprosy (lupus vulgaris) were included as controls. All biopsies were subjected to H & E, Modified Ziehl-Neelsen and S-100 immunostaining and were observed for following nerve patterns: infiltrated (A), fragmented (B), absent (C), and intact (D) nerves. The sensitivity of S-100 and H&E stain in nerve demonstration in tuberculoid cases and overall was calculated and compared.
Results: H&E Stain: Ten out of 30 (33.3%) cases demonstrated neural inflammation (inflammed). Among the 15 tuberculoid cases, only 6 (40%) cases showed neural inflammation, rest of the cases no nerve was demonstrable on H& E. No nerve was demonstrable in indeterminate cases. Contact group showed intact nerves in all cases.
S-100 Immunostain: On S-100 immunostaining, the most common pattern observed was nerve fragmentation (pattern B) seen in 15 (50%) cases, followed by absence of detectable nerves (pattern C) in 9 (30%) cases. Infiltrated pattern was seen in 6 (20%) cases. All the tuberculoid cases showed either of patterns of nerve involvement. The most common pattern observed was fragmented (pattern B) in 7/15 cases which was followed by absent pattern (pattern C) in 6/15 cases. Indeterminate cases had infiltrated pattern in all the cases. Lepromatous cases had fragmented pattern being commonest followed by absent pattern. All controls showed pattern D i.e. intact nerves. Intact nerve was not observed in any of the leprosy cases. The sensitivity of S-100 for demonstration of nerve in tuberculoid cases (BT and TT) was 100% and for H&E it was 40%.
Conclusion: S-100 aids in diagnosis in tuberculoid cases by nerve demonstration in the granulomas. It also helps in differentiating paucibacillary (BT and TT) leprosy from other granulomatous conditions.