Amelanotic subungual melanoma
Fewer than 7% of cutaneous melanomas lack pigment. In contrast, 20% to 33% of subungual melanomas are amelanotic. This makes the diagnosis of amelanotic subungual melanoma at best difficult, and often times impossible without a biopsy.1
Management of subungual melanoma
Nail biopsy
Untreated melanoma is potentially fatal, while nail biopsy is technically difficult, potentially disfiguring, and can be complicated by scarring or pterygium formation. The physician must thus carefully determine which lesions require biopsy. Except in the special case when the clinician deems the probability of subungual hematoma to be very high (discussed below), it may be best to refer these patients to a specialist when available.
As a general rule any nail lesion, whether pigmented or not, that does not heal with 6 to 12 weeks of conservative treatment should be biopsied. Lesions causing nail dystrophy, ulcerating lesions, and those presenting with Hutchinson’s sign should all be biopsied.
Caucasians. Managed conservatively, all single pigmented nail streaks in adult Caucasians unresolved within 6 to 12 weeks need to be biopsied. The clinician should thoroughly investigate non-melanotic causes of single pigmented streaks with a careful history and a thorough physical examination. Seek out clues, especially from the patient’s drug and treatment history. Unchanged, lightly pigmented streaks already present for many years on adult Caucasians at the time of initial presentation warrant close follow-up, and those with such lesions that remain unchanged after 6 to 12 months of follow-up may be safely discharged with instructions to seek medical evaluation if the lesion shows any subsequent morphological change.
Asians and dark-skinned persons. In contrast to pigmented nail streaks in Caucasians, dark-complected persons commonly exhibit melanonychia striata, and these streaks should not be routinely biopsied unless there has been some morphological change. Multiple streaks, streaks present on multiple nails, and those streaks that do not originate from the proximal nail fold are also unlikely to be melanoma in adults or children of any ethnicity, and these warrant clinical observation and a diligent search for another cause.1 The single exception to this is metastatic melanoma to the nail bed, which may present as multiple pigmented lesions on the same or different nails.