Hansen's disease (HD) is a chronic granulomatous inflammation primarily of the peripheral nervous system, skin, and reticuloendothelial system caused by Mycobacterium leprae.
HD manifests itself into two forms, namely tuberculoid and lepromatous that constitute two extremes of a continuous spectrum.
Histoid HD is a variant of lepromatous HD, which may occur before or during the treatment of HD, although it can also occur de novo.
The term histoid HD was coined by Wade (1963) who noticed histopathologically a picture of intertwined whorls and bands of spindle-shaped cells, together with areas which are entirely composed of large, round histiocytes massed with bacilli (globi) – "histoid habitus". The cellular infiltrates seemed to expand and push out the collagen matrix to form a pseudo capsule.
Clinically it is characterized by cutaneous and/or subcutaneous nodules and papules, which are painless, succulent, discrete, smooth, globular, skin-colored to yellowish-brown, with apparently normal skin surrounding it.
The lesions are usually located on the posterior and lateral aspects of the arms, buttocks, thighs, dorsum of the hands, lower part of the back, and over the bony prominences, especially over the elbows and knees.
In more severely affected cases, mucosal and genital lesions have also been recorded.
The palms and soles are usually spared.
Histoid lesions have also been reported to present along the course of the peripheral nerve trunks and cutaneous nerves. The ulnar nerve has been reported as the most common nerve involved.
Histoid HD clinically simulates xanthoma, neurofibroma, dermatofibroma, reticulohistiocytosis, or cutaneous metastasis. Biopsy of the lesion and a simple "Fite-Faraco stain" can confirm the diagnosis.
Treatment of histoid leprosy includes not only antimycobacterial therapy but also patient education about the disease, treatment of reactions, monitoring for and care of nerve damage, care of disabilities, social support, physical and occupational therapy, and rehabilitation.
References
Wade HW. The histoid variety of lepromatous leprosy. Int. J. Lepr. 1963; 31: 129.
Gupta SK. Histoid leprosy: review of the literature. Int J Dermatol. 2015;54:1283-8.
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