BOSTON — The threshold for biopsying unexplained nail dystrophy or discoloration should be low, according to Dr. Phoebe Rich.
Although most nail unit lesions are benign, “malignancies are not as obvious to spot clinically as you would think,” and a missed or delayed diagnosis can be life threatening, Dr. Rich said at the American Academy of Dermatology's Academy 2009 meeting.
Any unexplained solitary, painful, dystrophic nail, particularly in an elderly patient, should be biopsied to rule out squamous cell carcinoma of the nail bed. Any pigmented band of unknown etiology, especially in white patients, requires a biopsy to rule out melanoma, said Dr. Rich of the department of dermatology at Oregon Health and Science University in Portland.
The presence of certain clinical signs and symptoms can offer clues to the diagnosis of malignant neoplasms. For example, Dr. Rich said, squamous cell carcinoma of the nail may present as longitudinal erythronychia (a pinkish band extending from the nail matrix), as a nodule or tumor with or without nail loss, as a wartlike periungual lesion with nail splitting and skin fissure, or as a draining subungual mass. Because these presentations mimic other clinical entities, “you have to biopsy to get an accurate diagnosis.”
For the aforementioned lesions, “you can take a punch or a shave [nail bed] biopsy, and once you have a diagnosis, you can refer the patient for Mohs,” Dr. Rich said.
Subungual melanoma arises from the nail matrix and often presents initially as longitudinal melanonychia, Dr. Rich said. The differential diagnosis for melanonychia is broad, however, and includes benign nevi, lentigo in the nail matrix, genetic and ethnic-type pigmentation, subungual hematoma, drug-induced pigmentation, vitamin-deficiency fungal infections, and squamous cell carcinoma in situ, she said.
A high index of suspicion for melanoma should exist with lesions that begin under the nail and extend outward onto healthy skin around the nail (Hutchinson's sign), if there is variability in the pigmentation of the band, if the pigmented band is widening or growing, or if there is bleeding or signs of ulceration, Dr. Rich explained.
Although pigmentary changes can offer a clue to the presence of melanoma, a certain percentage of nail melanomas are amelanotic, Dr. Rich said. Amelanotic melanomas of the nail bed may resemble chronic paronychia or other benign nail conditions, she said.
For suspected nail melanoma, a nail matrix shave biopsy is sufficient, “unless you suspect advanced melanoma, which is characterized clinically by a dystrophic nail plate in addition to the pigmentation,” Dr. Rich said. “In that case, a full thickness biopsy is needed.”
For large lesions located in the lateral third of the nail, she added, “a longitudinal nail biopsy yields the best information because it samples the nail matrix, nail bed, nail fold, and hyponychium.”
Patients are typically apprehensive about nail surgery, so the onus is on the clinician to reassure them that it can be done painlessly by using appropriate and effective anesthesia, she noted.
Dr. Rich has received advisory board honoraria from Abbott Laboratories and investigator grants from Centocor Inc., Wyeth, and Genentech Inc.
Subungual melanoma, which arises from the nail matrix, often presents initially as longitudinal melanonychia.
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