An eight-year-old boy presented with an uncomfortable nodule under the distal great toenail (see the accompanying figure). The lesion was firm and fixed, and had not responded to the application of an over-the-counter remedy for warts (topical salicylic acid) or several trials of cryotherapy with liquid nitrogen.
The answer is B: plain radiograph of the toe. Subungual exostosis is an acquired, benign bony tumor that can affect any age group but most often is discovered in persons 10 to 30 years of age. It presents as a distal, subungual mass, usually on the dorsal-medial great toe. Fingernail lesions rarely occur. Subungual exostosis begins as a reactive fibrous growth that develops cartilage and ultimately ossifies. Complete excision remains the treatment of choice, although recurrences are reported. No gender or racial predilection has been noted.
In children, the differential diagnosis includes subungual wart and pyogenic granulomas, while the most serious condition would be a neoplasm such as osteochondrosarcoma, squamous cell carcinoma or glomus tumor.
Although the diagnosis can be made with a biopsy, radiographs to evaluate for bony involvement are recommended before biopsy of any subungual mass. In this case, if the physician were not prepared to remove bone, and expected only a soft tissue growth, the biopsy procedure would have been wasted.
Salicylic acid preparations, over-the-counter and prescription, may prove effective in the treatment of warts. Use of overnight occlusion may make the treatment more effective by hyperhydrating the wart, which may allow deeper penetration of the caustic medication. Topical tretinoin (Retin-A), topical 5-fluorouracil (Efudex), or both, may prove useful in the management of resistant warts (this is an off-label use). Excessive irritation is possible, especially if both of these agents are being used on the same patient (usually not at exactly the same time).
Subungual and periungual warts owe some of their resistance to treatment to several factors. The nail plate may shield a substantial portion of the wart, and partial removal of the nail may be necessary to surgically or medically approach the wart. Trauma, including nail-biting, aggressive manicures and even daily minor trauma, may help spread the wart from one part of the nail apparatus to another and even to other digits.