What is the most critical test to perform in a diabetic patient with a foot ulcer and nearly diminished sensation to assess neuropathy?

The Monofilament Test is the Most Critical Diagnostic Test

The 10-g monofilament test is the single most critical test to perform in this diabetic patient with a foot ulcer and diminished sensation, as it is specifically designed to diagnose loss of protective sensation (LOPS)—the primary underlying cause of diabetic foot ulceration. 1, 2

Why the Monofilament Test Takes Priority

The clinical scenario describes a patient who already has an established ulcer with "nearly diminished sensation"—this requires objective confirmation of LOPS rather than assumption based on history alone. 2 The monofilament test serves as the definitive diagnostic tool because:

• Peripheral sensory neuropathy is present in 78% of diabetic patients with foot ulcers, making it the single most common component cause for ulceration 1, 2
• The 10-g monofilament test is explicitly stated by the American Diabetes Association as the most useful and sensitive test for diagnosing LOPS and identifying feet at risk for ulceration 1
• The neurological examination in diabetic foot care is specifically designed to identify LOPS rather than early neuropathy, making monofilament testing the primary diagnostic tool for this exact clinical scenario 1, 2

Proper Testing Technique

Perform the 10-g monofilament test at multiple plantar sites (hallux, first metatarsal head, fifth metatarsal head as minimum) combined with at least one additional neurological assessment (pinprick, temperature perception with tuning fork, vibration with 128-Hz tuning fork, or ankle reflexes). 1

• Absent monofilament sensation confirms LOPS 1
• At least two normal tests with no abnormal findings rules out LOPS 1, 3
• Testing 3 sites per foot has similar diagnostic power to testing 10 sites, making it efficient for screening 4

Why Other Options Are Incorrect

ABI (Option A) is not the answer because:

• The patient has intact peripheral pulses, indicating adequate vascular supply 1
• ABI is indicated only when patients exhibit signs or symptoms of peripheral arterial disease (leg fatigue, claudication, decreased/absent pedal pulses) 1, 3
• This is a neuropathic ulcer (diminished sensation, well-demarcated plantar location), not an ischemic ulcer 2

CT scan (Option C) has no role in diagnosing LOPS or routine diabetic foot ulcer evaluation 1

Pressure assessment (Option D) becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading—not as the primary diagnostic test 2, 5

Critical Management Implications

Confirming LOPS through monofilament testing fundamentally changes the patient's management trajectory:

• Requires referral to foot care specialists for ongoing preventive care and lifelong surveillance 1
• Mandates specialized therapeutic footwear to redistribute plantar pressures 1, 5
• Necessitates foot inspection at every clinical visit rather than annually 1
• Stratifies the patient into high-risk category requiring examination every 1-3 months 5, 3

Common Pitfall to Avoid

Do not assume neuropathy exists based solely on the history of "nearly diminished sensation"—objective confirmation with monofilament testing is essential for proper risk stratification and evidence-based management planning. 2 The inability to feel a 10-g monofilament represents loss of approximately 98% of normal sensory ability, a threshold that predicts ulceration risk. 6