A 24-year-old Hispanic woman is referred to dermatology for a “fungal infection” that has failed to respond to topical (nystatin) and oral (fluconazole) treatments. The solitary lesion on her palm first manifested several months ago and is totally asymptomatic. Its appearance has fluctuated over time: fading then reappearing, and growing darker each time.

The patient’s health is otherwise excellent in almost every regard. Several years ago, she had a bladder infection and was prescribed trimethoprim/ sulfa; on the advice of her primary care provider, she continues to take one or two pills after sex to prevent another infection. This is her only prescription medication, but she acknowledges occasional use of OTC products and daily use of vitamins and a stool softener.

Examination reveals a dusky brown patch on the periphery of her left palm. There is no increased warmth or tenderness on palpation, and the lesion is nonblanchable. Palpation of local nodes fails to disclose any suspicious masses near the hand.

Elsewhere, her type IV skin is quite dark but unremarkable.