The Monofilament Test is the Most Critical Diagnostic Test
In a diabetic patient presenting with a non-healing foot ulcer and numbness, the 10-g monofilament test is the most critical test to perform to establish the diagnosis of loss of protective sensation (LOPS), which is the underlying cause in 78% of diabetic foot ulcers. 1, 2
Why Monofilament Testing Takes Priority
The clinical scenario describes a patient who already has an established ulcer with numbness—this presentation strongly suggests neuropathic ulceration. The diagnostic priority is to objectively confirm LOPS, which fundamentally changes management and risk stratification. 2
The Monofilament Test Establishes the Diagnosis
The American Diabetes Association explicitly states that neurological examination in diabetic foot evaluation is designed to identify LOPS rather than early neuropathy, making the 10-g monofilament the primary diagnostic tool for this exact clinical scenario. 2
Peripheral neuropathy with LOPS is present in 78% of diabetic patients with foot ulcers, making it the single most common component cause for ulceration. 1, 2
The monofilament test is one of the two most sensitive tests for identifying feet at risk for ulceration and is the most useful single test to diagnose LOPS. 2, 3
Proper Testing Technique
The monofilament should ideally be combined with at least one additional neurological assessment (pinprick, temperature, vibration with 128-Hz tuning fork, or ankle reflexes) to confirm the diagnosis. 1
Absent monofilament sensation confirms LOPS, while at least two normal tests with no abnormal tests rules it out. 2, 3
Testing can be performed at 3,4, or 10 sites per foot with similar diagnostic accuracy—the 3-site protocol (hallux, first metatarsal head, fifth metatarsal head) is sufficient and more practical. 4, 5
Why the Other Options Are Less Critical
ABI Testing (Option A) is Secondary
ABI is indicated for peripheral arterial disease (PAD) evaluation, not for diagnosing the underlying cause of a neuropathic ulcer. 2
Initial PAD screening should include clinical assessment of pulses, capillary refill time, rubor on dependency, and pallor on elevation before proceeding to ABI. 1
ABI with toe pressures is only indicated when patients have symptoms of claudication, rest pain, or absent pedal pulses on examination. 1
While PAD is present in up to 50% of diabetic foot ulcers, the clinical presentation here (numbness, inability to perceive touch) points to neuropathy as the primary pathology. 6
Pressure Point Assessment (Option C) is Part of Management, Not Diagnosis
Pressure assessment becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading. 2
Assessment of foot deformities and pressure points is part of the comprehensive foot examination but does not establish the diagnosis of LOPS. 1, 3
Critical Management Implications
The presence of LOPS fundamentally changes management, requiring: 2
- Specialized therapeutic footwear with appropriate offloading 1
- More frequent monitoring (not just annual screening) 3
- Referral to foot care specialists for ongoing preventive care and lifelong surveillance 1, 2
- Interprofessional approach with podiatry involvement 1
Common Pitfall to Avoid
Do not assume neuropathy based solely on the patient's history of numbness—objective confirmation with monofilament testing is essential for proper risk stratification and management planning. 2 The inability to feel a 5.07 monofilament represents loss of roughly 98% of normal sensory ability, a threshold that must be objectively documented. 7