De novo histoid leprosy.

Histoid leprosy is a rare form of multibacillary (MB) leprosy with unique clinical and histopathological features. However, the condition is not uncommon in India, and often it is poorly addressed. It is characterized by firm, dome-shaped, smooth, globular, painless, cutaneous, or subcutaneous nodules that appear on normal-looking skin.

A 50-year-old man presented with multiple firm, smooth, painless, non-itchy nodules over his abdomen, back, lower and upper limbs since one year. One week before, he had two episodes of epistaxis. On examination, multiple skin-colored, dome-shaped, non-tender nodules varying in size from 0.5 to 2 cm were found over the abdomen, back and both the upper and the lower limbs, more over the thighs [Figure 1] and knees [Figure 2]. There was partial claw hand [Figure 3] affecting four fingers of the right hand. Right ulnar nerve was thickened. There was no gynecomastia, depressed nasal bridge, loss of eyebrows or any ocular problem. There was no loss of sensation. There was no history of dapsone therapy or multidrug therapy (MDT) in the past. Hematologic findings including liver and renal function tests were normal, except a mildly elevated serum alkaline phosphatase level. Human immunodeficiency virus test was negative. Slit-skin smears examination from skin lesions yielded acid-fast bacilli (AFB) with a bacteriological index of 4+. Excisional biopsy from a firm nodule on abdomen showed a focally atrophied epidermis, beneath which the dermis was seen to contain a large circumscribed cellular infiltrate consisting of round-polyhedral foamy histocytes with vacuolated cytoplasm, and a fair number of plump spindle cells resembling fibroblasts, arranged randomly or in a whorl pattern [Figures 4 and 5]. An unusual histopathological feature was the absence of the grenz zone. Ziehl–Neelsen stain of the section showed abundant, mostly solid AFB within the foamy histocytes, with some lying extracellularly. The bacteriological index of lepra bacilli in the skin lesion was 4+. A final diagnosis of de novo histoid leprosy was made. The patient was placed on MB MDT with rifampicin, clofazimine and dapsone to which he responded within one month.

Figure 1

Dome-shaped, smooth nodules on normallooking skin of thigh

Figure 2

Classical nodules of histoid leprosy on knee

Figure 3

Claw hand involving four fingers of right hand

Figure 4

Photomicrograph showing atrophic epidermis, with dermis containing cellular infiltrate of round to polyhedral foamy histocytes with vacuolated cytoplasm and a fair number of plump spindle cells resembling fibroblasts, arranged in a whorled pattern (H and E, ×100)

Figure 5

Magnified histopathological image mimicking dermatofibroma (H and E, ×400)

Histoid leprosy usually presents as relapse of lepromatous leprosy after dapsone monotherapy (due to dapsone resistance), or at times de novo.[1] The reported incidence is 1-2% of the total number of leprosy patients,[2] with a male preponderance. It has been described in the age range of 10-84 years.[3] Histoid leprosy is characterized by nontender, smooth, globular, skin-colored nodules on apparently normal skin.[4] It is considered a variant of lepromatous leprosy and by others as a distinct entity.[45] De novo histoid leprosy is rare. The lesions are usually located on the posterior and lateral aspects of the arms, dorsum of hands, buttocks, thighs, legs, abdomen, and the back. It is more common on bony prominences, especially over the elbows and knees.[5] Histoid leprosy clinically simulates xanthoma, neurofibroma, dermatofibroma, and molluscum contagiosum [Figure 6]. Histopathological findings of histoid leprosy include epidermal atrophy as a result of dermal expansion of the underlying leproma and acellular band (grenz zone) located below the epidermis. Dermis is filled with fusiform histocytes arranged in a whorled or criss-cross pattern. These histocytes resemble fibroblasts.

Figure 6

A histoid leprosy nodule on abdomen mimicking molluscum contagiosum

Health workers and doctors attached with leprosy elimination drive should be educated about distinct features of histoid leprosy so that the movement to search out new cases could be intensified. Not a single patient of histoid leprosy must remain undetected since he/she is a reservoir of bacilli.