SAN DIEGO Extracutaneous melanomas are rarethey make up only 15% of all melanomasbut small primary lesions can be easily overlooked during a routine skin exam, according to one expert.
Sites that require close inspection include the scalp, nail beds, interdigital folds, and perianal skin. These areas "are easily accessible to clinical exam and can make a big difference for your patients," Dr. Terence C. O'Grady said at an update on melanoma sponsored by the Scripps Clinic.
The most commonly affected sites for extracutaneous melanoma include the ocular or juxtacutaneous mucosal membranes, said Dr. O'Grady, who directs the dermatology residency program at the University of California, San Diego.
The three most common metastatic locations include the lungs (70%), the liver (68%), and the bowels (58%). Other sites include the pancreas (50%), the adrenal gland (50%), the heart (49%), kidneys (45%), brain (39%), thyroid (39%), and spleen (36%), he said.
Melanoma can metastasize to these sites in a number of ways. A melanoma could have been completely removed without histologic examination.
"You could also have a completely regressed melanoma at another site that was not treated," he said.
"This can be a real problem because there is no evidence of a pre-existing lesion. In our clinic, if we don't see a primary lesion we do a Wood's light exam and look for hypopigmented areas that may represent previously regressed lesions. Unfortunately, when you biopsy these regressed areas, the only thing you usually see is pigment incontinence on the histology, so there's no evidence that the melanoma was ever there," Dr. O'Grady said.
Because it's rare to find primary melanomas in these locations, he continued, "it's more probable that these lesions are metastatic to that site rather than being a primary lesion."
The five most common locations of primary extracutaneous melanoma include the eye (79%), the vulva (7%), soft tissues (3%), anorectum (2%), and the vagina (2%), according to Dr. O'Grady. "Many of us loathe to do an exam of the genitalia, but [lesions in this area] do occur," he said. "I usually tell patients that have had a melanoma or are at high risk for melanoma to bring this point up with other physicians they [may see], so they can have those areas examined."
Dr. O'Grady said that he begins his skin examinations at the scalp and works his way down to the feet.
"I always tell patients who wear nail polish to have that removed for the exam so I can see the nail bed," he said. "I look at the interdigital folds and at the bottom of the feet. Patients always wonder, 'What are you looking for in between my toes?' I tell them, 'You can get pigmented lesions in those areas. You can also get melanomas in those areas.'"
He also emphasized the importance of biopsying lesions detected in subungual areas. "These lesions can be impossible to diagnose without a biopsy, but a lot of [clinicians] don't feel comfortably doing a nail biopsy," said Dr. O'Grady.
"Not only is that a problem, but when you send it to pathology and you don't have someone who knows how to handle nail specimens, you're going to end up with a very nondiagnostic specimen. You want to see the skin on top of the nail, the nail plate, and the subungual tissue," he said.