Monofilament Test (Option B)
The monofilament test is the most critical test to confirm the diagnosis of loss of protective sensation (LOPS) in this patient with a non-healing plantar diabetic foot ulcer and numbness. 1, 2
Why Monofilament Testing is the Answer
The clinical presentation—numbness, inability to perceive touch/sensation, and a plantar ulcer—strongly suggests LOPS as the underlying diagnosis. The 10-g monofilament test is specifically designed to identify LOPS, which is the single most common component cause of diabetic foot ulceration, present in 78% of diabetic patients with ulcers. 1, 2
Key diagnostic principle: The monofilament test doesn't diagnose early neuropathy—it identifies LOPS, which is the critical threshold that predicts ulceration risk and fundamentally changes management. 2, 3 When a patient cannot feel the 10-g monofilament, they have lost approximately 98% of their sensory ability compared to normal individuals. 4
Why the Other Options Are Less Critical
ABI (Ankle-Brachial Index) - Option A
- ABI is indicated for evaluating peripheral arterial disease (PAD), not for diagnosing the neuropathic cause of this ulcer. 1, 2
- The clinical scenario lacks vascular symptoms (no mention of claudication, rest pain, or absent pulses). 1
- Critical caveat: ABI is actually unreliable in diabetic patients due to noncompressible vessels from medial arterial calcification; toe pressures are more accurate when vascular assessment is needed. 1
- While PAD evaluation is important in diabetic foot ulcers, the prominent feature here is sensory loss, making neuropathy confirmation the priority. 1
Assessment of Pressure Points - Option C
- Pressure point assessment becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading. 2
- This is a management tool rather than a diagnostic test for the underlying pathophysiology. 1
Proper Testing Protocol
The monofilament test should ideally be combined with at least one additional neurological assessment to confirm LOPS: 1, 3
- Pinprick sensation (small fiber function)
- Temperature perception (small fiber function)
- Vibration with 128-Hz tuning fork (large fiber function)
- Ankle reflexes
Diagnostic interpretation: Absent monofilament sensation confirms LOPS, while at least two normal tests with no abnormal tests rules it out. 2, 3
Clinical Impact on Management
Confirming LOPS through monofilament testing immediately triggers high-risk classification and changes management: 2, 5
- Referral to foot care specialist for ongoing preventive care
- Specialized therapeutic footwear with pressure redistribution
- More frequent monitoring (every 1-3 months, not just annually)
- Patient education on daily foot inspection
- Aggressive offloading strategies for the current ulcer
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 presence of an ulcer with sensory symptoms makes the diagnosis clinically obvious, but formal monofilament testing documents the severity of LOPS and guides the intensity of subsequent interventions. 1, 3