What is the most critical test to perform in a diabetic patient with a non-healing foot ulcer, numbness, and inability to perceive touch and sensation?

Most Critical Test: 10-g Monofilament Testing

In a diabetic patient presenting with a non-healing foot ulcer, numbness, and inability to perceive touch and sensation, the 10-g monofilament test (Option B) is the most critical diagnostic test to perform, as it is specifically designed to identify loss of protective sensation (LOPS)—the single most common component cause for diabetic foot ulceration, present in 78% of cases. 1

Why Monofilament Testing is the Answer

Primary Diagnostic Purpose

• The neurological exam in diabetic foot evaluation is explicitly designed to identify LOPS rather than early neuropathy, making the monofilament test the primary diagnostic tool for this exact clinical scenario 1, 2
• The 10-g monofilament is the most useful test to diagnose LOPS and represents one of the two most sensitive tests for identifying feet at risk for ulceration 1, 2
• Peripheral neuropathy was found to be a component cause in 78% of diabetic patients with ulcerations, with the triad of peripheral sensory neuropathy, minor trauma, and foot deformity present in >63% of cases 1

Clinical Context of This Case

• This patient already has the ulcer and clinical signs of neuropathy (numbness, inability to perceive touch), but the diagnosis of LOPS must be objectively confirmed with monofilament testing for proper risk stratification and management planning 2
• The presence or absence of LOPS fundamentally changes management, requiring specialized footwear, more frequent monitoring, and referral to foot care specialists 2
• Do not assume neuropathy based solely on history—objective confirmation is essential 2

Why Other Options Are Less Critical

Option A: Ankle-Brachial Index (ABI)

• ABI testing is indicated for evaluating peripheral arterial disease (PAD), not for diagnosing the underlying cause of a neuropathic ulcer 1, 2
• Initial PAD screening should include history of leg fatigue, claudication, and assessment of pedal pulses 1
• ABI is only performed when there are symptoms or signs of PAD, not as the primary diagnostic test for a neuropathic presentation 1
• The question provides no mention of absent pulses, claudication, or vascular symptoms—the presentation is clearly neuropathic 1

Option D: Assessment of Pressure Points

• Pressure assessment becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading 2
• This is a secondary intervention, not the critical diagnostic test 1

Proper Testing Technique

Monofilament Application Protocol

• Test at three sites on both feet: plantar surface of the first toe, third metatarsal head, and fifth metatarsal head 1
• Apply perpendicular to skin surface with sufficient force to cause the filament to bend or buckle 1
• Total duration of approach, skin contact, and removal should be approximately 2 seconds 1
• Repeat application twice at the same site, alternating with at least one mock application (total three questions per site) 1
• Protective sensation is present if the patient correctly answers two out of three applications at each site 1

Confirmation Testing

• 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 LOPS 1
• Absent monofilament sensation plus one other abnormal test confirms the presence of LOPS 1
• At least two normal tests (with no abnormal test) rules out LOPS 1

Evidence Strength

Guideline Consensus

• The American Diabetes Association (2024,2018) explicitly recommends the 10-g monofilament as the primary screening tool for LOPS 1
• The International Working Group on the Diabetic Foot (2016) provides detailed technical guidance on monofilament application 1

Research Support

• Clinical examination and the 10-g monofilament test are the two most sensitive tests in identifying patients at risk for foot ulceration, with sensitivity reaching 99% when combined with clinical examination 3
• Monofilament testing demonstrated 100% sensitivity in identifying patients with foot ulcers, superior to biothesiometry 4
• The monofilament examination is a reproducible, valid, and generalizable test recommended as the screening procedure of choice for examining diabetic feet 5

Critical Clinical Pitfall

The most common error is assuming neuropathy based on symptoms alone without objective monofilament testing. This patient's inability to perceive touch strongly suggests LOPS, but formal monofilament testing is required to:

• Confirm the diagnosis objectively 2
• Document baseline sensory status 1
• Trigger appropriate high-risk management protocols 1
• Guide referral to foot care specialists 1