The Monofilament Test is the Most Critical Diagnostic Test
The 10-g monofilament test is the single most critical test to perform in this patient, as it objectively confirms loss of protective sensation (LOPS)—the underlying diagnosis that explains the clinical presentation and fundamentally determines management. 1
Why the Monofilament Test Takes Priority
The clinical scenario describes a patient with "nearly diminished sensation"—this is a subjective observation that requires objective confirmation through standardized testing. The monofilament test serves as the definitive diagnostic tool because:
- LOPS is present in 78% of diabetic patients who develop foot ulcers, making it the single most common causative factor for diabetic foot ulceration 1
- The American Diabetes Association explicitly states that the neurological exam is designed to identify LOPS rather than early neuropathy, positioning the monofilament test as the primary diagnostic tool for this exact clinical scenario 2, 1
- The monofilament test is one of the two most sensitive tests for identifying feet at risk for ulceration and serves as the foundation for risk stratification and management planning 1
- Absent monofilament sensation confirms LOPS, while at least two normal neurological tests (with no abnormal test) rules it out 2, 3
Proper Testing Technique
The 10-g monofilament should ideally be performed with at least one additional neurological assessment (pinprick, temperature perception with a 128-Hz tuning fork, or ankle reflexes) to confirm the diagnosis 2, 3, 4. This combined approach increases diagnostic accuracy and provides comprehensive neurological assessment.
Why Other Options Are Not the Answer
ABI Testing (Option A)
- ABI is indicated only when patients have symptoms of claudication or decreased/absent pedal pulses 2
- This patient has intact peripheral pulses, making PAD evaluation secondary 3
- ABI evaluates vascular disease, not the neuropathic cause of this plantar ulcer 1
CT Scan (Option C)
- No guideline or evidence supports CT scanning as a diagnostic test for neuropathic foot ulcers in this clinical context
- CT would be considered for suspected osteomyelitis or Charcot arthropathy, neither of which is suggested by this presentation
Pressure Point 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
- While elevated barefoot peak plantar pressures >4.1 kg/cm² can identify sites at risk for ulceration 5, this assessment follows—not precedes—the diagnosis of LOPS
- Pressure assessment is a management tool, not a diagnostic test for the underlying neuropathy
Critical Clinical Pitfall
Do not assume neuropathy based solely on history or clinical impression—objective confirmation with monofilament testing is essential for proper risk stratification and management planning 1. The inability to feel a 5.07 monofilament represents a sensory threshold more than 50 times greater than normal, meaning roughly 98% of sensory ability has been lost 6. This objective measurement transforms clinical management by:
- Triggering referral to foot care specialists 2
- Mandating specialized therapeutic footwear 2, 1
- Requiring more frequent monitoring (every 1-3 months for high-risk patients) 3
- Establishing the need for patient education on daily foot inspection 4
The monofilament test has proven prognostic value, with relative risk for future foot ulceration ranging from 2.5 to 7.9 in patients with positive results 7, making it not just diagnostic but also prognostically essential for preventing recurrence.