A 27-year-old man, who works as an electrician, self-refers for evaluation of changes on his left palm. He first noticed them three years ago, when a scaly patch appeared on his volar wrist. At the time, his mother sent him an unidentified cream from Mexico, which he used on the rash. Although it resolved, within a few months, his entire palm was similarly affected.
The problem has persisted despite a number of treatment attempts—with, among other things, OTC creams and lotions, topical steroids, antifungals, and two courses of oral antibiotics. He even tried a vegetarian diet. Nothing has worked.
The hand is mildly symptomatic and faintly irritated. He reports similar symptoms on the soles of both feet, which he says date to several years before his hand problem. The fingernails on the affected hand have also changed.
The skin and nails of his right hand have remained completely normal throughout this experience. His health is otherwise excellent.
EXAMINATION
The skin on his left palm and on both soles is identical: uniformly scaly and pink, and in sharp contrast to the normal, smooth skin of his right palm. All five fingernails of his left hand are yellowed, thickened, and dystrophic. Surprisingly, all toenails are normal in appearance. His right hand is unaffected.
What is the diagnosis?