Several months ago, a 51-year-old woman first noticed brownish red lesions on her leg. She initially dismissed them as insect bites and regarded them as mostly a cosmetic concern. When the lesions failed to disappear after six months, her primary care provider referred the patient to dermatology. (In the interim, a friend did suggest ringworm as a diagnosis, but the OTC tolnaftate cream the patient tried had no effect.)
The patient claims to be quite healthy, which she attributes to walking several miles a day and working out at the gym every other day. She denies any shortness of breath, unexplained fever, or night sweats. There is no personal history of diabetes, but she has had glucose tolerance tests every six months for years because of a significant family history of the disease.
There are four intradermal shiny round nodules, averaging about 1.8 cm, on the upper anterior tibial area. The margins of the lesions are sharply drawn, and there is no surrounding erythema or increased warmth on palpation. The surfaces are quite uniform in texture.
Examination of her skin elsewhere reveals no noteworthy lesions. There is no palpable adenopathy in the groin on the affected side.
Results of a punch biopsy show interstitial and palisaded granulomas of the subcutaneous tissue, especially the dermis. Thickening of blood vessel walls and endothelial cell swelling are also noted.
What is the diagnosis?