This patient has a neuropathic ulcer. Neuropathic ulcers often occur on the lower extremities in patients with peripheral neuropathy and other disorders of sensation. They result from repetitive trauma; patients are often unaware of the injury because of the lack of pain or other discomfort. The asymptomatic nature of most neuropathic ulcers highlights the need for clinical testing for neuropathy (by monofilament testing) and routine surveillance for ulcers in patients at high risk, such as this woman with long-standing diabetes mellitus. Neuropathic ulcers are usually noninflamed, have well-demarcated borders, and are often surrounded by signs of recurrent friction such as callus. The ulcers may be quite deep and occasionally extend to bone, increasing the risk for osteomyelitis. They typically occur over pressure points on the feet. Treatment consists of debridement of devitalized tissue, removal of friction, protection of the area, and treatment of any co-existing infection.

Arterial ulcers may also occur over bony prominences in patients with diabetes (since many patients with diabetes mellitus have peripheral vascular disease), but they are usually quite tender and have significant surrounding erythema. They may also occur on the pretibial aspects of the lower legs.

Squamous cell carcinomas may occur on the lower extremities and appear as nonhealing ulcers. They typically occur in sun-exposed areas such as the pretibial lower legs rather than the plantar feet. They are usually inflamed and are not surrounded by callus or other signs of chronic friction.

Venous stasis ulcers generally occur on the medial aspects of the lower legs and are surrounded by dyspigmentation and induration consistent with lipodermatosclerosis. Intermittent stasis dermatitis flares are also commonly seen.