BALTIMORE Nail dystrophy and a history of trauma should raise suspicion of subungual epidermoid inclusions, Dr. Beth S. Ruben said at the annual meeting of the American Society of Dermatopathology.
Dr. Ruben and her colleagues have encountered 17 such cases. Common clinical impressions included pachyonychia, hemorrhage, onychomycosis, or carcinoma.
"The fingers and thumb were involved more than the toes," she said. Fingers and thumbs were affected in nine cases, toes were affected in seven cases, and location was not specified in one case. "In some cases [12], there was nail dystrophy either clinically or histologically," said Dr. Ruben of the University of California, San Francisco.
In five cases, there was evidence of trauma. Calcification was noted in four cases.
Histologically, look for small, pale clusters of keratinocytes forming small cysts that resemble the follicular isthmus, or even ductal epithelium, and small, solid aggregates. Sometimes there might be an underlying bony abnormality, and there might be associated hyperkeratosis of the nail bed, she said.
Subungual cysts can be classified using a system developed by Italian investigators (Dermatologica 1989;178:20912).
Type I inclusions are quite superficial. Nails might appear normal or exhibit clubbing. Less cystic variants can be mistaken for neoplasms.
Type II inclusions are more extensive. The nail bed might be hyperkeratotic. Cysts can be superficial or deep. The nail plate might be thickened. Most of the cases in the series reported by Dr Ruben were of the superficial type (type I).
The differential diagnosis should include subungual keratoacanthoma and ony-cholemmal carcinoma, Dr. Ruben said.