Background:Histopathologic diagnosis of borderline tuberculoid leprosy (BTL) is fraught with hurdles. It overlaps with other granulomas and documenting nerve involvement is the key to correct diagnosis. This is difficult on H and E sections alone. S-100 immunostaining may help in this regard.Objectives:To study the patterns of nerve involvement in BTL and other cutaneous granulomas using S-100 immunostain and compare its sensitivity with that of H and E staining, in both adequate and inadequate biopsies.Materials and Methods:A total of 20 cases of BTL were reviewed. And, 19 biopsies from other cutaneous granulomas were taken as controls. S-100 immunostaining was done on paraffin sections. The pattern of nerve involvement was graded as intact, infiltrated and/or fragmented, intact with perineural inflammation.Results:Of the 20 cases of BTL, S-100 demonstrated infiltrated and/or fragmented nerves in 15 and absent nerves in 5 cases. H and E stain identified neuritis in eight cases. The sensitivity of S-100 and H and E is 0.78 and 0.41. In the 19 controls, S-100 identified normal nerves in 16 with 7 showing perineural inflammation only and their absence in 2 cases. H and E identified normal nerves in nine cases. The sensitivity of S-100 and H and E is 0.83 and 0.41. In biopsies where subcutis was absent, the sensitivity of S-100 in identifying nerve involvement is 0.66 compared with H and E 0.33.Conclusion:S-100 staining is an efficient ancillary aid in distinguishing BTL from other granulomas and is superior to H and E in identifying nerve involvement, even where subcutis is absent. Infiltration and/or fragmentation of nerves by S-100 is the only reliable marker of BTL.

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Significantly higher values were noted in the dimensions of TK using M1. High significant positive correlations were observed in measurements made by the two methods. The CS ostium was relatively constantly placed within the TK.