S-100 as a useful auxiliary diagnostic aid in tuberculoid leprosy

The diagnosis of tuberculoid leprosy is often difficult on hematoxylin and eosin (H&E) due to the absence of demonstrable nerve destruction. This study evaluates the utility of S-100 staining in identifying nerve fragmentation and differentiation of tuberculoid leprosy from other cutaneous granulomatous diseases.

Fifty cases of leprosy including 38 borderline tuberculoid (BT), two tuberculoid (TT), and 10 indeterminate leprosy (IL) were studied. Eleven controls of non-lepromatous cutaneous granulomatous lesions were included. S-100 was used for identifying the following dermal nerve patterns: infiltrated (A), fragmented (B), absent (C), and intact (D) nerves.

On H&E, only 18/38 (47.4%) BT cases and 1/2 (50%) TT cases revealed neural inflammation. On S-100 staining of BT cases, 28/38 (73.7%) showed pattern B followed by patterns C and A in 8/38 (21.1%) and 2/38 (5.3%) cases, respectively. Both the TT cases showed pattern B. Only intact nerves (D) were seen in all the control cases. S-100 identified nerve damage in 4/10 (40%) IL cases. The patterns A, B, and C had sensitivity, specificity, and positive and negative predictive values of 100% in diagnosing tuberculoid (BT + TT) leprosy.

S-100 is superior to H&E in identifying nerve fragmentation (p < 0.01). It also aids the differential diagnosis of tuberculoid leprosy.