Melanoacanthoma, a very rare lesion,[1] was originally described by Bloch in 1927 as “non-nevoid melanoepithelioma type1.”[2] The term “melanoacanthoma” was first coined by Mishima and Pinkus in 1960, who considered this benign pigmented lesion being composed of both melanocytes and keratinocytes.[3] This neoplasm represents a slowly growing, usually solitary, growth of head and neck, or trunk, of older people.[4–6] Melanoacanthoma clinically simulate seborrheic keratosis or a melanoma and may attain a diameter of 3 cm or more.[7] According to the current view, melanoacanthoma denotes a rare variant of seborrheic keratosis rather than a distinct entity,[2] that differs from the usual type of pigmented seborrheic keratosis by marked increase in the concentration of melanocytes. The melanocytes are scattered throughout the tumor lobules instead of confining only to the basal layer.[8] These melanocytes are large and highly dendritic and they contain varying amounts of melanin. Melanoacanthoma has also been reported to origin from mucous membrane, which are rare reactive type of mucosal melanotic macule, unrelated to seborrheic keratosis.[9] An Indian report of multiple genital and perianal melanoacanthomas up to size of 6 cm has been published.[10]

A 65-year-old male presented with painful, localized plaque on left side of lower back. The patient had a small indistinct pigmented patch at the same site, which first appeared during his childhood. Five years back the present lesion appeared on the previous patch, then gradually enlarged and became itchy and rose above the skin surface. Initially the lesion was dry, scaly, not painful and but in recent years it turned out to be highly painful. By profession, he was a farmer belonging to lower socioeconomic category. He, as a farmer, had been exposed to scorching sunlight on his back for almost the whole day. He had the history of addiction to smoking, tobacco chewing, and alcohol intake. He had been suffering from tuberculosis of chest in the past and presently from bronchial asthma and mild depression. On systemic examination no relevant abnormality was found. Dermatological examination revealed that the oval lesion [Figure 1] was of maximum diameter 10 cm × 5 cm, markedly tender, having brown to blackish pigmentation, well-defined margin, and verrucous surface. On palpation, the lesion was indurated. No lymphadenopathy was detected in neighboring feeding sites. Laboratory investigations including routine hematological and biochemical comprising hepatic and renal profiles and urine examination were all within normal limit. Chest X-ray PA view, ultrasonography of whole abdomen did not reveal any abnormal lymph node or visceral change.

Cutaneous melanoacanthomas manifest as pigmented papules, plaques, cutaneous horns or nodules. Melanoacanthomas have been described more frequently in white patients. They develop in the middle-aged and the elderly like any other type of seborrheic keratosis. They are found mainly on the trunk or head, often on the lip or eyelid. Melanoacanthoma, a benign mixed tumor of melanocytes and keratinocytes,[3] although rare, may clinically mimic pigmented seborrheic keratosis and malignant melanoma.[7] However characteristic histopathological features will differentiate the above three lesions. Two histologic types of melanoacanthomas are described: a diffuse type in which melanocytes are unevenly scattered throughout the lesion and a clonal type in which melanocytes and keratinocytes are clustered in small nests. There was partial or complete disturbance of transfer of melanin from these highly dendritic melanocytes to neighboring keratinocytes. Immunofluorescent studies and an immunoprecipitin assay have shown that melanoacanthomas are not related to malignant melanoma, and hence, removal by simple excision, curettage or cryotherapy should be curative.[10]