Subungual malignant melanoma

Introduction

Subungual malignant melanoma is a rare disease with reported incidence between 0.7% to 3.5% of all melanoma cases in the general population.[1] The incidence of malignant melanoma is much lower in the Japanese than in the Caucasians. However, the subungual and periungual sites are commonly found in the Japanese, amongst the various types of malignant melanomas.[2]

Case Report

A 43-year-old tailor presented with progressive blackish discolouration and destruction of left middle finger nail of 1 year duration. There was history of trauma with sewing machine needle on the same nail with through and through penetration 12 years back. However, the injury healed uneventfully with the patient absolutely asymptomatic in the intervening decade. A year back, he noticed an inconspicuous longitudinal brown-blackish streak over the nail, which had progressed to the present state with topical and oral antifungals taken from general practitioner of no avail. Dermatological examination revealed black dystrophic left middle finger nail plate, with easy friability and partial destruction of the nail plate. There was leaching of black pigment at the proximal nail fold, i.e., positive Hutchison′s sign [Figure - 1]; however regional lymphadenopathy was absent. Systemic examination and routine investigations like haemogram, urinalysis, BSL, USG abdomen, CT scan abdomen were within normal limits.

Patient underwent disarticulation at the proximal interphalangeal joint [Figure - 2]. Gross examination of specimen showed 2 x 1.2 cms black swelling on the dorsal aspect of terminal interphalangeal joint. Small cavity filled with black-brown material was seen on serial cut sections with deep invasion of upto 0. 5 cm. Resection margin was free of tumour tissue. Microscopy study showed tumour consisting of cells arranged in the form of nests and groups in subepithelial location. Individual cells were round to oval filled with melanin. Deep dermal invasion was seen. However, resection margin was free of tumour cells.

Discussion

Majority of the subungual melanomas start with a longitudinal brown streak in the nail. However, brown to black nail pigmentation may be due to different colouring substances of exogenous and endogenous origin. Exogenous pigmentations usually are not streaky or do not present as a stripe of even width with regular borders. Bacterial pigmentation, commonly due to Pseudomonas aeruginosa or proteus species have a greenish or grayish hue and the discolouration is often confined to the lateral edge of the nail. Subungual haematoma may result from a single heavy trauma or repeated microtrauma which often escapes notice. Although oval in shape, it does not form a neat streak. Melanin pigmentation in the form of a longitudinal streak in the nail is due to a pigment-producing focus of melanocytes in the matrix.[3]

In one study on subungual melanomas, finger nails were affected in 62% and toe nails in 38%. The thumb and great toe nails were affected in 73%.[2] Other studies, also confirm the most common sites of involvement as the great toes, followed by thumb. For the early detection and thus survival of patients of sub ungual malanoma, the ABCDF rule of sub ungual malanoma was devised.[1] In this system, A stands for age (peak incidence being in the 5th to 7th decades of life) and African Americans, Asians and native Americans in whom sub ungual melanoma accounts for upto 1/3rd of all melanoma cases. B stands for brown to black and with breadth of 3 mm or more and variegated borders. C stands for change in the nail band or lack of change in the nail morphology despite adequate treatment. D stands for the digit most commonly involved, E stands for the extension of the pigment onto the proximal and/or lateral nail fold (i.e., Hutchison′s sign) and F stands for family or personal history of dysplastic nevus or melanoma.

Subungual malignant melanoma is rare in the Indian set up. Trauma sustained over the same nail more than a decade back was probably coincidental. He should consider himself lucky that there was no apparent metastasis, given the metastatic potential and rapid spread of malignant melanoma. He satisfied criteria ABC and E of Levits rule for clinical detection of subungual melanma.[1] namely age in 5th decade, black discolouration, change in nail morphology leading to dystrophy of nail plate and positive Hutchison′s sign.