Melanoma of the nail is usually a variant of a melanoma arising on the palms of the hands and soles of the feet. It may occur on any fingernail or toenail, with a greater incidence on the great toe and thumb. It is not thought to be due to sun exposure, but trauma may be a risk factor. Melanoma of the nail unit is somewhat rare, accounting for only about 1% melanoma in white-skinned individuals. It arises in people of all races; however, it is the most common type of melanoma diagnosed in deeply pigmented individuals. It is most commonly diagnosed between the ages of 40 and 70.
Nail melanoma often starts as a pigmented band visible the length of the nail plate. Over weeks to months, the pigment band becomes wider, especially at its proximal end towards the cuticle, more irregular in pigmentation, extends to involve the adjacent nail fold, may develop a nodule, ulcerate or bleed, or may cause thinning, cracking or distortion of the nail plate. However, in up to half of all cases subungual(under nail) melanoma is not pigmented. Ungual melanoma can form a nodule under the nail plate, lifting it up. It may sometimes look like a wart. It is usually painless, but an advanced tumor invading underlying bone may cause severe pain.
The diagnosis of a subungual melanoma may be suspected clinically because of a wide (>3mm) new or changing pigment band in a single nail. Ungual melanoma forms a non-pigmented lump under the nail plate, eventually resulting in its destruction. The diagnosis of melanoma is confirmed by biopsy of the nail matrix and nail bed. The melanoma may be either in-situ or invasive and this is determined by the pathologist.
If the clinical diagnosis is subungual hematoma (a purple mark under the nail due to bleeding or bruising), the nail may be observed for a few weeks. Normal-appearing nail should then be seen growing behind the mark. Other diagnoses that are often considered include onychomycosis (fungal infection), paronychia, pyogenic granuloma, or squamous cell carcinoma.
Once the diagnosis of nail melanoma is confirmed, the patient is usually referred to see a melanoma specialist and hand surgeon. Melanoma in the nails must be removed surgically. This requires removal of the entire nail apparatus. Sometimes the end of the finger or toe is amputated. Some patients may be offered sentinel node biopsy to determine whether the melanoma has spread to local lymph nodes. The main factor associated with risk of spread of melanoma (metastasis) and death is the thickness of the melanoma at the time of complete excision of the primary tumor. Delay in diagnosis is common with subungual melanoma, particularly when it affects the toe, and some of these tumors have already spread at the time of diagnosis.