A rare case of subungual melanoma.

A 51-year-old male presented with blackish discoloration of nails of 10 months duration. Examination revealed black dystrophic left thumb finger nail. Detailed examination showed a mass under the dystrophic nail. Hutchinson sign was positive. Histopathology revealed characteristic features of melanoma. A detailed evaluation revealed no features of local or distant metastasis. The entire lesion was then removed surgically along with disarticulation at the interphalangeal joint. Resection-free margin was confirmed. This case is being reported for the rare occurrence of subungual melanoma in the Indian population and also for presentation with a long history of lesion with no evidence of metastasis.

What was known?

Subungual melanoma is a rare melanoma globally.

Melanoma by itself is reported rarely from the Indian population.

Introduction

Subungual melanoma or melanotic whitlow is a relatively rare disease with a reported incidence between 0.7% and 3.5% of all melanoma cases in the general population.[1] Despite the significant improvement in the diagnosis of cutaneous melanomas, the diagnosis of subungual melanoma still remains difficult. Despite its visibility and easy accessibility, it is often misdiagnosed, and thus there is a delay in treatment. This delay in recognition often results in a poor prognosis.[2] All persistent nail lesions, which do not respond to conservative treatment, whether pigmented or not, should undergo excisional biopsy and pathologic examination. A case of subungual melanoma is presented to highlight the typical presentation and clinical characteristics, which help in its early diagnosis and subsequent management. Early detection and awareness is the key to successful treatment outcome and prognosis of the patients.

Case Report

This 51-years-old male patient presented with a 10 months history of gradually progressive blackish discoloration of his left thumb nail. There was associated history of insidious onset gradually progressive swelling of the distal aspect of left thumb. Mild pain was present. There was no history of any trauma prior to onset of complaints. There was no discharge or itching. He had taken multiple oral and topical medicines including several courses of oral anti-fungals with no relief.

Dermatological examination revealed diffuse mildly tender swelling involving distal part of left thumb, distal to the interphalangeal joint [Figure 1a]. The overlying nail plate was hyperpigmented and dystrophic. Hyperpigmentation was also present on the proximal nail fold, hyponychium, and periungal areas (positive Hutchinson's sign). There were islands of black necrotic granulation tissue with scant purulent non-foul smelling discharge in between the layers of the dystrophic nail plate [Figure 1b]. There was no regional lymphadenopathy.

Figure 1

(a) Dystrophic thumb nail with hyperpigmented nail bed swelling and positive Hutchinson’ sign, (b) Close up view of the same

Systemic examination was normal. Biopsy from left thumb nail bed on histopathological examination revealed features of malignant melanoma. Investigations like hemogram, urinalysis, liver and renal functions, ultrasound abdomen, and CT scan abdomen were within normal limits. Detailed evaluation including PET scan did not reveal any features of metastasis.

Patient underwent excision of the entire lesion along with disarticulation at the interphalangeal joint. Resected margins were found to be free of tumor tissue [Figure 2]. Histopathology revealed sheets of cells varying in shape from polygonal to spindle [Figure 3]. The spindle cells had scanty cytoplasm, pleomorphic oval to spindle hyperchromatic nuclei. Some of these nuclei were angulated. Some cells were polygonal with large coarse nuclei and prominent macronucleoli. Many of the cells contained intracytoplasmic golden brown pigment. Areas of necrosis and mitotic figures were seen. A final opinion of malignant melanoma was given based on the histopathological features.

Figure 2

Excised tumor revealing tumor-free margins (tumor excised in toto) [H and E stain, ×10]

Figure 3

Histopathology revealed sheets of cells varying in shape from polygonal to spindle, which had scanty cytoplasm and pleomorphic oval to spindle hyperchromatic nuclei. Many of the cells contained intracytoplasmic golden brown pigment, and areas of necrosis and mitotic figures were seen. [H and E stain, ×10]

Discussion

Pigmented lesions of the nail unit may be due to a wide variety of benign and malignant causes. Melanoma is the commonest malignant lesion seen in the nail unit. Subungal melanoma is a rare form of melanoma. Overall, 62% of subungual melanomas present under the fingernails with 38% presenting under toe nails.[3] Subungual hematoma, pyogenic granuloma, or onychomycosis may have a similar clinical presentation.[4]

Histological diagnosis is the most definitive way of identifying such a lesion and can prevent significant morbidity and mortality. Suspicious signs to be aware of are nail fold pigmentation (Hutchinson›s sign), lifting off of the nail from the nail bed, and ulcerating lesions that do not heal.[5] A very useful approach is the ‘ABCDEF’ rule,[1] for the clinical detection of subungual melanoma as given in Table 1. These can be applied in a similar fashion to the ‘ABC’ approach of detecting cutaneous melanoma, which has led to early identification.

Table 1

Features of subungual melanoma

Estimated 5-year survival is between 16% and 87%.[6] Prognosis depends heavily upon the thickness of the tumor, termed the Breslow thickness, the stage of the tumor, and the degree of tumor invasion. Breslow thickness is known to be a good prognostic indicator for subungual melanoma, even though it is less accurate than that for cutaneous melanoma. Up to 25% of patients can present with lymph node or distant metastases.

Subungual melanoma presents in a more disguised manner than cutaneous lesions and, therefore, requires increased vigilance and awareness.[78] That is why any unresolving subungual lesion of any kind should raise a suspicion until proven otherwise, and early biopsy of the lesion is warranted as soon as possible along with a thorough clinical examination of regional and distant lymph nodes. Early detection in malignant melanoma is vital for improved treatment outcomes and prognosis.

Due to extreme rarity in the Indian population, subungual melanoma is rarely reported in literature from this country,[910] and cases are missed in their earlier stages. Another interesting fact is the absence of local or distant metastasis despite the long history.

What is new?

This is a very rare presentation of subungual melanoma in the Indian literature. (Only two previous reports of subungual melanoma could be traced in Indian literature).

Subungual melanoma can remain localized despite a long history of presentation.