A 59-year-old woman presents urgently to dermatology for evaluation of very itchy lesions that manifested at least 20 years ago. They have been previously diagnosed as staph infection, fungal infection, psoriasis, and scabies but have not responded to a variety of topical steroid creams and topical antibacterials (eg, triple-antibiotic cream, mupirocin, and clindamycin solution). The patient has also been prescribed numerous oral antibiotics, the most recent of which was a 10-day course of clindamycin. This induced a raging case of diarrhea; her primary care provider subsequently referred her to dermatology.
She denies any family history of skin problems until her sister, who has accompanied her to this appointment, mentions that she and her mother have had similar problems for decades. More questioning reveals that all three women also have extensive psychiatric histories of chronic anxiety and depression.
When pressed, the patient and her sister admit to picking at their skin “constantly,” but especially when under stress.
EXAMINATION
Most of the patient’s lesions—round to oval, orangish red, scaly plaques that range from 2 to 5 cm—are on her legs, below her knees. There are about 15 lesions total. They look and feel very thick but have no increased warmth or tenderness. The erythema is confined to the lesions and does not extend into the surrounding areas.
Punch biopsy of one leg lesion shows a hypertrophic epidermis with focal parakeratosis, elongation of rete ridges, and perhaps most importantly, no signs of other items in the differential (such as psoriasis or skin cancer).
Elsewhere on her skin, extensive punctate disciform scarring extends across her upper back, stopping abruptly at the T2 level. The skin below remains totally clear.
What is the diagnosis?