Background Rare variants of leprosy pose a diagnostic challenge even to astute clinicians and histoid leprosy is one such form of disease with unique clinical and histopathological features. There are very few large series on this entity, mainly reported from India.
Objectives To study the epidemiological and clinical characteristics of patients with histoid leprosy.
Methods We undertook this retrospective study including patients registered with the leprosy clinic of our tertiary care referral centre from January 1991 to December 2006. Data regarding demographic details, clinical features, treatment, complications and course following treatment were extracted from the records of the leprosy clinic.
Results The incidence of histoid leprosy among the registered patients of our clinic was 1·8% (40 of 2150). There was a significant male preponderance with a male/female ratio of 5·7 : 1. The anatomical areas of involvement were thighs/buttocks (67·5%), arms (62·5%), back (52·5%), face (47·5%), forearms (47·5%) and legs (35%) in descending order of frequency. This variety of leprosy was found most commonly in patients with a primary diagnosis of lepromatous leprosy (40%). De novo histoid lesions, i.e. lesions of histoid leprosy developing without evidence of lesions of other types of leprosy in the Ridley–Jopling classification, appeared in 12·5% of patients only. Only three patients had received antileprosy treatment before presentation. Episodes of erythema nodosum leprosum (ENL) had occurred in 40% of patients, although only one patient manifested ENL after the diagnosis of histoid leprosy. The disease responded satisfactorily to the respective World Health Organization multidrug therapy regimens in all except in one patient who relapsed with borderline lepromatous leprosy.
Conclusions As the bacillary load is very high in these patients, they can form a potential reservoir of the infection in the community especially in the postleprosy elimination era. Contrary to the earlier belief in the dapsone era, most of our patients manifested disease without any history of inadequate or incomplete antileprosy therapy.