Children. Subungual melanoma is quite rare in children of any race, though the incidence is not zero. As such, any new pigmented streak warrants observation by the physician, while pre-existing streaks unchanged for several years may by monitored by the parent and child. Any morphological change in a pre-existing streak or change in a new streak requires biopsy in all adults and children.
Conducting a nail biopsy
When the clinician believes a diagnosis of subungual hematoma is likely, a simple office procedure and test will often confirm the diagnosis.6 Any family physician can perform this procedure and test, saving the patient both time and the expense of obtaining a consultation, and sparing both patient and physician the anxiety of waiting days or even weeks to rule out a potentially life-threatening diagnosis.
Procedure. First, soak the hand (or foot) in warm water for 10 to 15 minutes to soften the nail plate. Next, drive a 3- or 4-mm punch biopsy through the nail plate, being careful not to injure the underlying nail bed, as any bleeding will invalidate the subsequent test. To minimize the risk of traumatizing the nail bed, avoid local anesthesia. Once you remove the specimen, grasp it with a pair of forceps and inspect it closely.
If the pigment does not adhere to the undersurface of the nail plate, but instead the biopsy specimen is clean, with the pigmented part being the nail bed itself, the diagnosis of subungual hematoma is virtually excluded, mandating a biopsy of the nail bed. If the underside of the nail specimen is pigmented, use a #15 blade to carefully scrape the pigment onto the sample surface of a standard hemoccult card. Add a drop of water to the pigment scrapings; then the card is developed in the usual fashion. A positive test indicates the presence of old blood and confirms the diagnosis of subungual hematoma. You should make sure to follow-up periodically to assure that the pigment recedes as the nail grows, as well as to confirm the absence of any further lesion is still required—keeping in mind that nail trauma precedes a large percentage of subungual hematoma.
Staging
Once the diagnosis of subungual melanoma is confirmed the depth of invasion must be determined. Clark’s level of invasion may be poorly defined in subungual melanoma, due to unique histopathological characteristics of the nail bed. Breslow’s absolute depth correlates less closely with prognosis of subungual melanoma than with cutaneous melanoma, but tumor thickness has been found to be a good prognostic indicator of subungual melanoma.1