An unusual presentation of De-novo Histoid leprosy clinically mimicking as neurofibromatosis

Histoid leprosy is a rare and uncommon variant of lepromatous leprosy which generally occurs following resistance to dapsone therapy or relapse after dapsonemonotherapy or multidrug therapy. Rarely, it can occur de novo without any history of treatment. We present one such rare case of de-novohistoid leprosy mimicking neurofibromatosis presented in a 43 year old male. © 2020 Published by Innovative Publication. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by/4.0/)


Introduction
Histoid leprosy is a well acknowledged entity in lepromatous patients presenting as characteristic cutaneous or subcutaneous nodules and plaques over the skin. The term "Histoid leprosy" was originally coined by Wade in 1963 as a histological concept of bacillary-rich leproma composed of spindle-shaped cells, along with the absence of globus formation (so conspicuous in ordinary leproma). In chronic form however it exhibits a fibromatoid tendency. 1 Since then many cases have been reported in the literature. 2 We hereby present one such case of denovohistoid leprosy mimicking neurofibromatosis in a 43 year old man.

Case Report
A 43 year old male presented with complaints of multiple skin coloured nodular painless, non-tender lesions measuring 0.5-1 cm over the right forearm, right shin, left ankle and dorsum of left foot (total 5 in number) since 6 months ( Figure 1a). Many tender nodules were also noted on the gluteal region. There was no loss of sensation or nerve thickening. There was no past history of similar lesions and a negative drug intake history for leprosy. General physical and systemic examinations turned out to be normal.
Clinically, differential diagnosis included neuromas, xanthomas, neurofibromas, dermatofibroma and histoid leprosy being last on the list. Biopsy from the forearm lesion was taken and sent for histopathological examination.
Microscopically, sections showed thinned out epidermis with underlying clear grenz zone (Figure 1 b). Dermis and subcutaneous tissue revealed round to spindle shaped histiocytes arranged haphazardly and admixed with foamy macrophages (Figure 1 c).Focally spindle cells were arranged in whorled and criss-cross/storiform pattern.
Modified Fite-Faraco Stain for lepra bacilli showed numerous acid-fast lepra bacilli arranged in globi and scattered singly (Figure 1 d). The bacilli appeared as uniform solid stained, long rods with tapering ends with a bacterial index of 6+ and morphological index of >70%.

Discussion
The incidence of histoid leprosy among leprosy patients is estimated to be 2.79-3.60%. It shows male preponderance and an average age of diagnosis is 21-40 years. 3 It is clinically characterised by cutaneous or subcutaneous nodules and papules which are painless, firm, discrete, smooth, globular, skin coloured to yellowish brown in appearance located on arms, buttocks, thighs, dorsum of hands, lower back and bony prominences. 1 The lesions show characteristic histopathological features most important being its well circumscribed nature, abundance of spindle shaped and/or polygonal cells and a large number of acid fast bacilli. These lesions are most often located in dermis and/or subcutis surrounded by a pseudocapsule as a result of compressed adjacent tissue. 1 It further shows epidermal atrophy and an acellular band located below the epidermis (Grenz zone). The dermis consists of fusiform histiocytes arranged in whorled, crisscross and storiform pattern, containing acid fast bacilli. 4 Histoid leprosy is so called because the microscopic appearance of the nodule shows spindle shaped cells resembling those in dermatofibromas.
It can clinically mimic neurofibromas, xanthomas, dermatofibromas, reticulohistiocytosis and cutaneous metastasis. Each of these can be differentiated on the basis of histopathology, mycobacterial absence on slit skin smear and nerve thickening. 5 No nerve thickening or anaesthetic lesions were seen in our case, which was probably the reason that the clinical diagnosis of histoid leprosy was lower down on the list of differential diagnosis. However, histopathological examination revealed plenty of acid fast bacilli with bacterial index of 6+ confirming the diagnosis of histoid leprosy.
Palit and Inamdar have suggested that the histoid form of leprosy could serve as a reservoir of leprosy and as a source of new cases. 6 Hence, a high index of suspicion for histoid leprosy is important for early diagnosis and treatment of these cases and for control of spread of the disease.

Conclusion
In the post elimination era of leprosy, a high index of suspicion is of utmost importance to continue surveillance for new and relapse cases and for their early diagnosis and treatment.

Source of funding
None.

Conflict of interest
None.