What is the most critical test to perform to diagnose a diabetic patient with a well-demarcated plantar foot ulcer, diminished sensation, and intact peripheral pulses, presenting with signs of diabetic neuropathy and impaired perception and touch sensation?

Monofilament Test is the Most Critical Diagnostic Test

The 10-g monofilament test is the most critical test to perform in this patient, as it objectively confirms loss of protective sensation (LOPS), which is the single most common component cause of diabetic foot ulceration and fundamentally determines the diagnosis and subsequent management strategy. 1

Why Monofilament Testing Takes Priority

The clinical presentation strongly suggests a neuropathic ulcer based on:

• Well-demarcated plantar location (classic for neuropathic ulcers) 1
• Nearly diminished sensation (suggesting LOPS but requiring objective confirmation) 1
• Intact peripheral pulses (making ischemia less likely as the primary etiology) 1
• Central erythema with healing signs (consistent with pressure-induced neuropathic ulceration) 1

The neurological examination is specifically designed to identify LOPS rather than early neuropathy, making the monofilament test the primary diagnostic tool for this exact clinical scenario. 2 The American Diabetes Association explicitly states that the 10-g monofilament is the most useful test to diagnose LOPS and is one of the two most sensitive tests for identifying feet at risk for ulceration. 1, 2

Why Other Options Are Not the Priority

ABI Testing (Option A)

• ABI is indicated when there are symptoms or signs of peripheral arterial disease (claudication, decreased/absent pulses, leg fatigue). 1
• This patient has intact peripheral pulses, making significant PAD less likely as the primary cause. 1
• ABI should be performed in patients with symptoms of claudication or decreased/absent pedal pulses, which this patient does not have. 1
• While vascular assessment is important, it is not the most critical test when pulses are intact and the presentation is classic for neuropathic ulceration. 1

CT Scan (Option C)

• CT imaging has no role in the initial diagnostic workup of diabetic foot ulcers for determining the underlying etiology (neuropathic vs. ischemic). 1
• Advanced imaging like CT angiography is reserved for vascular assessment when revascularization is being considered, not for diagnosing the cause of the ulcer. 1

Pressure Assessment (Option D)

• Pressure assessment becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading. 1, 2
• Evidence of increased plantar pressures (erythema, warmth, calluses) guides management decisions about footwear, but does not establish the diagnosis of LOPS. 1

Diagnostic Technique and Interpretation

The monofilament test should ideally be performed with at least one other neurological assessment (pinprick, temperature, vibration with 128-Hz tuning fork, or ankle reflexes) to confirm the diagnosis. 1

Interpretation criteria:

• Absent monofilament sensation confirms LOPS 1
• At least two normal tests with no abnormal test rules out LOPS 1
• The combination of abnormal monofilament testing with one other abnormal neurological test provides the strongest diagnostic confirmation 1

Clinical Impact on Management

Confirming LOPS fundamentally changes management and requires:

• Specialized therapeutic footwear with demonstrated pressure relief 1, 2
• More frequent monitoring and detailed foot assessments 1
• Referral to foot care specialists for ongoing preventive care and lifelong surveillance 1
• Patient education on daily foot inspection using alternative sensory modalities (visual inspection, palpation) 1

Critical Pitfall to Avoid

Never assume neuropathy based solely on history of diminished sensation—objective confirmation with monofilament testing is essential for risk stratification and management planning. 2 The presence of peripheral neuropathy was found to be a component cause in 78% of diabetic patients with ulcerations, making its objective documentation paramount. 1

While this patient will eventually need comprehensive assessment including vascular evaluation, the immediate diagnostic priority is confirming LOPS with monofilament testing, as this establishes the neuropathic etiology and drives all subsequent management decisions. 1, 2