Monofilament Test is the Most Critical Diagnostic Test
The 10-g monofilament test is the most critical test to perform in this patient to confirm loss of protective sensation (LOPS), which is the underlying diagnosis driving this clinical presentation. 1, 2
Why Monofilament Testing is Essential
The clinical presentation strongly suggests a neuropathic ulcer:
- Well-demarcated plantar location (classic for neuropathic ulcers) 3
- Nearly diminished sensation (requires objective confirmation) 2
- Intact peripheral pulses (rules out ischemic etiology as primary cause) 1
Peripheral neuropathy with LOPS is the single most common component cause for diabetic foot ulceration, present in 78% of diabetic patients with ulcers. 1, 2 The monofilament test is explicitly designed to identify LOPS rather than early neuropathy, making it the primary diagnostic tool for this exact clinical scenario. 2
Diagnostic Confirmation Protocol
Perform the 10-g monofilament test combined with at least one additional neurological assessment (pinprick, temperature perception with 128-Hz tuning fork, or ankle reflexes) to confirm LOPS. 1, 2, 4
- Absent monofilament sensation confirms LOPS 2, 4
- The combination of monofilament testing with one additional modality substantially increases specificity with minimal loss of sensitivity 5
Why Other Options Are Not the Answer
ABI testing (Option A) is indicated for peripheral arterial disease evaluation, not for diagnosing the underlying cause of a neuropathic ulcer. 2 Since this patient has intact peripheral pulses, vascular insufficiency is not the primary concern. 1
Assessment for pressure points (Option D) becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading. 2 While elevated plantar pressures >4.1 kg/cm² are associated with DFU risk 6, pressure assessment is a management tool, not a diagnostic test for the underlying neuropathy.
CT scan (Option C) has no role in diagnosing LOPS and would only be considered if osteomyelitis or Charcot arthropathy were suspected based on clinical findings.
Critical Clinical Pitfall
Do not assume neuropathy based solely on history of "nearly diminished sensation"—objective confirmation with monofilament testing is essential for risk stratification and management planning. 2 The presence of LOPS fundamentally changes management, requiring specialized footwear, more frequent monitoring (every 1-3 months for high-risk patients), and referral to foot care specialists. 2, 4