Derm Dx: Discoloration on the buttocks and lower back

A 52-year-old woman with a history of chronic vertebral disk problems and lumbar surgery is referred for evaluation of a discoloration affecting her buttocks and lower back. She denies symptoms related to the dermatitis, but she has had chronic use of a heating pad in an attempt to alleviate underlying back pain. Examination reveals a well-demarcated zone of hyperpigmented confluent ...