Since early summer, a 51-year-old woman has had an itchy rash on her trunk. It manifested after she intentionally lost more than 200 lb, which resulted in deeper and more pronounced skinfolds. The same skinfolds are repeatedly involved in flares of the rash, which is worse on particularly hot days. She was diagnosed with “yeast infection” but the problem failed to respond to oral fluconazole and topical nystatin.
The patient has multiple health problems, including diabetes, chronic anxiety, and hypertension.
There is a deep, linear, concave fold in the skin of the right flank, the long axis of which is transversely oriented. Within this fold, a fiery red rash is seen; its margins exactly match the outline of skin-on-skin contact. The surface of the affected skin is macerated and wet looking. There is neither tenderness nor increased warmth on palpation.
What is the diagnosis?