What is classified as a diabetic ulcer?

What is Classified as a Diabetic Ulcer

A diabetic ulcer is defined as a full-thickness wound below the ankle in a person with diabetes mellitus, typically occurring on the plantar aspect of the foot, resulting from the pathophysiologic triad of peripheral neuropathy, peripheral artery disease, and trauma with or without secondary infection. 1, 2, 3

Core Pathophysiologic Components

The International Working Group on the Diabetic Foot (IWGDF) establishes that diabetic foot ulcers arise from three interconnected mechanisms 2, 3:

• Peripheral neuropathy causing loss of protective sensation, leading to unrecognized trauma, foot deformities, and callus formation 2, 3
• Peripheral artery disease (PAD) present in up to 50% of diabetic foot ulcer cases, causing ischemia and impaired wound healing 4
• Trauma or pressure to the insensate foot, often minor and unnoticed by the patient 2, 3

Clinical Presentation and Location

Diabetic ulcers characteristically present as 5, 3:

• Full-thickness skin loss extending through the dermis 1
• Plantar location in the majority of cases, though ulcers can occur anywhere on the foot 3
• Absence of pain in many cases due to neuropathy, which paradoxically delays presentation 2

Essential Diagnostic Criteria

The American Diabetes Association and IWGDF require assessment of specific features to properly classify a diabetic ulcer 6, 7:

• Presence of diabetes mellitus as the underlying condition 1
• Vascular status assessment including palpation of dorsalis pedis and posterior tibial pulses, ankle-brachial index (ABI <0.9 indicates PAD), and toe pressures 4, 6
• Neurological assessment using 10-g monofilament testing to confirm loss of protective sensation 6
• Infection status determined by presence of at least two inflammatory signs (redness, warmth, induration, pain/tenderness) or purulent secretions 6

Classification by Ulcer Type

The IWGDF distinguishes diabetic ulcers into three categories based on pathophysiology 6, 5:

• Neuropathic ulcers: Adequate perfusion with loss of protective sensation, typically painless with good pulses 6
• Neuro-ischemic ulcers: Combined neuropathy and PAD, the most common presentation affecting up to 50% of cases 4, 6
• Purely ischemic ulcers: Predominantly vascular insufficiency with intact sensation, less common 6, 5

Critical Distinction from Other Wound Types

Diabetic ulcers must be distinguished from other wound types that can occur in diabetic patients 5:

• Venous ulcers occur on the medial malleolus with characteristic hemosiderin staining and lipodermatosclerosis 5
• Arterial ulcers present on the lateral malleolus or toes with a "punched-out" appearance 5
• Diabetic bullae, furuncles, cellulitis, and carbuncles are distinct entities not classified as diabetic foot ulcers 5

Epidemiologic Context

The lifetime risk of developing a diabetic foot ulcer ranges from 19% to 34% in persons with diabetes 8, 9. Once an ulcer develops, the 5-year recurrence rate is 65%, lifetime amputation risk is 20%, and 5-year mortality reaches 50-70% 9. These devastating statistics underscore why precise classification at initial presentation is critical for appropriate management and improved outcomes 5.

Common Pitfall to Avoid

Do not classify a wound as a "diabetic ulcer" simply because the patient has diabetes. The wound must demonstrate the characteristic pathophysiologic features of neuropathy and/or ischemia with trauma, typically located below the ankle 6, 5. Wounds in diabetic patients from other etiologies (venous insufficiency, pressure injury on the heel in a bedridden patient, traumatic laceration with normal sensation and perfusion) should be classified according to their primary pathophysiology 5.