Nodular leprosy of childhood and tuberculoid leprosy: a comparative, morphologic, immunopathologic and quantitative study of skin tissue reaction.Int J Lepr Other Mycobact Dis. 2003 Sep;71(3):218-26.

Nodular leprosy of childhood (NL) is a benign clinical variant of tuberculoid leprosy that affects breast-feeding infants and children that remained in a highly infected environment. The lesions resolve with complete healing and NL has been considered a manifestation of allergy and congenital immunity to Mycobacteria leprae. We studied the tissue reaction, Mycobacterial antigen frequency, and the lymphocyte subsets (CD45RO+, CD4+, CD8+, B, NK), dendritic cells (epidermal CD1a+ cells and S100+ dermal dendrocytes), and macrophages in skin lesions of a clinically well characterized NL group (N = 11). Results were compared to children (N = 23) and adults (N = 24) with classical tuberculoid leprosy. NL lesion histopathology was characterized by dense granulomatous inflammatory reaction, with a greater number of confluent tubercles when compared to the other groups. Neural compromise was seen in all biopsies. The frequency of Mycobacterium antigen was similar in all groups. The population of CD45RO+, CD4+ and CD8+ T lymphocytes, natural killer cells, B lymphocytes, CD1a+ epidermal cells, and macrophages of NL lesions did not differ from the other groups. The number of S100+ dermal dendritic cells of the NL group was smaller than that of the adult group, although it did not differ from the other group of children. Except for the confluent tubercules, our data could not disclose any other difference in the tissue reaction of NL, in spite of its peculiar clinical features and evolution when compared with the classical tuberculoid leprosy. The localization of NL lesions may be the result of the intimate skin contact with lepromatous parents or relatives, in areas such as cheeks, arms, buttocks, and limbs, and the innoculation of M. leprae into skin may strongly stimulate cell mediated immunity (CMI) against the bacilli. These circumstances might explain the good CMI response leading to high resistance, stability, and auto-resolution of nodular leprosy of childhood.

S-100 as a useful auxiliary diagnostic aid in tuberculoid leprosy. J Cutan Pathol. 2006 Jul;33(7):482-6.

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

Histo-bacteriological investigation on borderline tuberculoid leprosy. Nippon Rai Gakkai Zasshi. 1991 Jul-Dec;60(3-4):152-7.

The multi-sections, which were stained by Fite method, of skin biopsies taken from twelve active BT cases were examined under the guidance of special stains for demonstration of nerve components. All cases were AFB positive. Bacilli were found in infiltrated nerves in 11 cases, of which, in 7 cases, bacilli were detected in nerve fragments within epithelioid cell granuloma. And bacilli were seen in arrector pili muscles in 2 cases. No bacilli were detected in other sites. Since the survival of M. leprae in nerves is one of the reasons causing relapse, this paper suggests that it would be better to treat active BT cases with multibacillary regimen recommended by WHO even though smear-negative.