BOSTON The threshold for biopsying unexplained nail dystrophy or discoloration should be low, according to Dr. Phoebe Rich.
Although the majority of 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," she said, stressing that nail surgery should not be intimidating. "Any dermatologist who can do a punch biopsy can do a nail biopsy."
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 or, if you feel confident, you can remove it yourself," said Dr. Rich. "We all do skin surgery for squamous cell carcinoma day in and day out. When you remove it, you just have to remember that there is no subcutaneous tissue in the nail, so you are actually removing it at the level just at the periosteum. Check to make sure you have got a nice margin, and you're in good shape."
Subungual melanoma arises from the nail matrix and often presents initially as longitudinal melanonychia, said Dr. Rich. 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. "In these cases, when you have a pigmented band, you have to open it up, look in there, and get a specimen," she said. "It's critical that you biopsy proximally at the matrix, at the origin of the band, because you need the melanocytes. If you biopsy the nail bed distally in an area where the nail plate is involved, you're not going to get the pigment, and you won't get an accurate diagnosis."
Although pigmentary changes can offer a clue to the presence of melanoma, a certain percentage of nail melanomas are amelanotic, said Dr. Rich. 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, "a longitudinal nail biopsy yields the best information because it samples the nail matrix, nail bed, nail fold, and hyponychium."
Proper preparation of the specimen is also critical to an accurate diagnosis, stressed Dr. Rich, who always orients the specimen on a paper template with a schematic of the nail and fingertip to duplicate its position on the nail unit before dropping it into formalin. "This way, the pathologist knows where the sample comes from," she said.
Because patients are typically apprehensive about nail surgery, the onus is on the clinician to reassure them that it can be done painlessly by using appropriate and effective anesthesia, according to Dr. Rich, who often begins the anesthesia application by having the patientespecially if it is a childhold a vibrating device. This offers a distraction, she explained, and provides a competing sensation. She then administers an ethyl chloride spray, followed by an injection, via a 30-gauge needle, of lidocaine with epinephrinewhich has been proved safe. The addition of bupivacaine or ropivacaine helps to minimize postoperative discomfort.