Monofilament Test is Most Critical
The 10-g monofilament test is the most critical diagnostic test to perform in this clinical scenario, as it specifically identifies loss of protective sensation (LOPS)—the primary underlying pathophysiology responsible for this patient's non-healing plantar ulcer. 1, 2
Why Monofilament Testing Takes Priority
The clinical presentation already strongly suggests LOPS based on the patient's numbness and inability to perceive touch and sensation. However, objective confirmation with monofilament testing is essential because it fundamentally changes management, requiring specialized footwear, more frequent monitoring, and referral to foot care specialists. 1
Key Diagnostic Principles
LOPS is present in 78% of diabetic patients with foot ulcers, making it the single most common component cause for diabetic foot ulceration 1
The American Diabetes Association explicitly states that the neurological exam is designed to identify LOPS rather than early neuropathy, making monofilament testing the primary diagnostic tool for this exact clinical scenario 1
The 10-g monofilament test is one of the two most sensitive tests for identifying feet at risk for ulceration and has proven prognostic value with relative risks for ulceration ranging from 2.5 to 7.9 in patients with positive results 1, 3
Why Not ABI in This Context
ABI testing evaluates for peripheral arterial disease (PAD), not for diagnosing the underlying cause of a neuropathic ulcer. 1 While vascular assessment is important in comprehensive diabetic foot care, this patient's presentation (plantar location, numbness, loss of sensation) points to a neuropathic rather than ischemic etiology. The absence of pulse documentation in the stem further suggests the primary concern is confirming neuropathy, not vascular disease.
Why Not Pressure Assessment Alone
Pressure assessment becomes relevant after confirming LOPS through monofilament testing, as part of the treatment strategy involving therapeutic footwear and offloading. 1 It's a management tool, not a diagnostic one for establishing the presence of LOPS.
Proper Testing Protocol
The monofilament should ideally be performed with at least one additional neurological assessment (pinprick, temperature, vibration with 128-Hz tuning fork, or ankle reflexes) to confirm the diagnosis 4, 1, 2
Absent monofilament sensation confirms LOPS, while at least two normal tests (with no abnormal test) rules it out 1, 2
Testing at 3-4 sites per foot is sufficient and as effective as testing 10 sites, making it practical for clinical use 5, 6
Critical Clinical Pitfall
Do not assume neuropathy based solely on history—objective confirmation with monofilament testing is essential for risk stratification and management planning. 1 The patient's symptoms strongly suggest LOPS, but documentation of objective findings drives the intensity of preventive interventions and specialist referral.