Sir,

Histoid leprosy (HL) constitutes a rare variant of multibacillary (MB) leprosy characterized by distinctive clinical and histopathological characteristics. Although the lesions of HL seldom exhibit ulceration, the literature inadequately explores the presence of Mycobacterium leprae in the epidermis in HL cases. We recently saw three cases of HL, in whom the clinical presentation included ulceration, and subsequent histopathological examination revealed trans-epidermal elimination (TEE) of leprosy bacilli. These cases each featured multiple raised skin lesions on the face and trunk, accompanied by ulcerated and eroded lesions on the extremities. Prior history of trauma was excluded and a family history of similar lesions or multidrug therapy (MDT) intake was absent. Cutaneous examination revealed multiple dome-shaped, non-umbilicated, succulent papules, and nodules over the face, abdomen, back and extremities.

One of the patients displayed larger ulcerated lesions on the lateral malleolus of left foot and instep (Figure 1). For the others, the nodular lesions over both upper limbs, trunk, palms and soles were associated with overlying erosions. Multiple peripheral nerves were enlarged in all the cases and glove and stocking anaesthesia was present in one instance. Slit skin smear (SSS) examination unveiled multiple slender elongated acid-fast bacilli (AFB) with a bacterial index (BI) of 6+. Dermatopathology (H and E stain) revealed multiple spindle cell histiocytes in the dermis arranged in whorled and storiform pattern, admixed with foamy histiocytes, lymphocytes, and a few plasma cells (Figure 2). Fite staining demonstrated leprosy bacilli in the dermis and various epidermal layers, indicative of TEE of leprosy bacilli (Figure 3). Based on the clinical presentation and histopathological examination, the final diagnosis of de novo histoid leprosy was considered. MB-MDT was initiated, leading to complete ulcer healing and a 50–60% reduction in nodule size after one month of therapy.

HL manifests with asymptomatic firm, dome-shaped succulent papulo-nodular lesions on seemingly normal skin or subcutaneous tissues. Notably, ulceration of histoid lesions is very rare.1–4 While an anecdotal report proposed Type 1 reaction as the cause for the ulceration,5 our current cases lacked clinical or histopathological signs of Type 1 reactions. Remarkably, TEE of leprosy bacilli was evident in the present cases.

The postulated pathomechanism behind TEE suggests that bacilli present in the upper dermis are assimilated by basal cells and transported upwards within epidermal cells before being expelled from the stratum corneum into the environment.6 Notably, Namisato et al. reported TEE of M. leprae in scar-forming umbilicated nodules in lepromatous leprosy, attributing it to rapidly growing dense granulomas in the upper dermis.7 However, the coexistence of non-ulcerated HL with TEE remains largely unexplored, with isolated anecdotal reports encountering TEE in ulcerated HL lesions.4,8,9

Sehgal and Srivastava postulated that ulceration in HL could stem from the host’s efforts to eliminate bacilli, possibly involving augmented cell mediated immunity.1 Similarly, Singh et al. proposed that augmented immunity linked to Type 1 reactions, might contribute to ulceration.5 However, a comprehensive analysis of the literature did not reveal conclusive causative factors for ulceration or distinct histopathological correlations in the remaining cases.2–4,8–10

In conclusion, the potential co-occurrence of ulcerated HL with TEE raises questions about its significance and association. This report also challenges existing perceptions of the aetiology of ulceration in histoid lesions, particularly in the absence of Type 1 reactions. We propose the hypothesis that granulomas loaded with bacilli infiltrating the basal layer of the epidermis, coupled with TEE, could underpin ulceration in these cases. Notably, this holds significance as dissemination of leprosy bacilli could heighten transmission risks. Further investigations are required to elucidate these intriguing aspects.