A 10-year-old girl is seen in dermatology for evaluation of dry skin. She reports few if any symptoms but expresses frustration at her inability to curb the problem; she’s tried several different moisturizers to no avail.
Additional history-taking reveals that she’s had patches of dry skin since age 4; these have appeared and disappeared on her arms, legs, and neck. None has ever been problematic enough to require medical attention.
But recently, a dry patch manifested on the patient’s forearm that her primary care provider diagnosed as fungal infection. Unfortunately, the prescribed antifungal creams (terbinafine and clotrimazole) had no positive impact on the situation.
The patient and her mother deny any family history of skin disease.
EXAMINATION
The scaly, annular plaque on the patient’s extensor left forearm is distinctly salmon-pink, with a tenacious white scale. Elsewhere, there are scaly areas in both post-auricular sulci. There are no significant changes to the skin on the patient’s knees, elbows, or scalp. Several tiny pits are observed on her fingernails.
What is the diagnosis?