The differential diagnosis consists of psoriasis, wart, eczema, squamous cell carcinoma in situ, and prurigo nodularis. What’s your diagnosis?
This 58-year-old man was concerned about a dime-sized red, scaly, painless patch on his knuckle. It did not itch or burn; the patient did not habitually rub, pick, or scratch the lesion. There were no similar lesions on either hand; no epitrochlear or axillary adenopathy was detected. The genitalia were free of lesions, and there was no history of genital warts. The patient had a history of basal cell carcinoma on the arm and several more recent actinic keratoses on a balding scalp.
What's your diagnosis?