Subungual keratoacanthoma.

Only 12 cases of lesions reputed to be subungual keratoacanthomas have been reported to our knowledge, and those have not been unequivocal by histologic and biologic criteria. Those 12 lesions have been tabulated by us and reviewed critically. In addition, we now provide two cases of keratoacanthomas in the subungual region that are histologically typical of keratoacanthomas found on hair-bearing skin. It appears to us that subungual keratoacanthoma is a specific type of keratoacanthoma that differs from the common solitary keratoacanthoma on hair bearing skin by 1) its similarity to verruca vulgaris clinically; 2) having more dyskeratotic cells and fewer neutrophils and eosinophils histologically; 3) being more vertical in orientation (longer than it is broad); 4) its failure to regress spontaneously; 5) its longer course; and 6) its tendency to destroy bone. Paradoxically, keratoacanthoma situated in the subungual region is a more destructive neoplasm than a squamous cell carcinoma there.