Most Important Diagnostic Test: Monofilament Test
The monofilament test is the most important diagnostic test for this patient, as it objectively confirms loss of protective sensation (LOPS), which is the single most common cause of diabetic foot ulceration and fundamentally changes management. 1, 2
Why Monofilament Testing Takes Priority
Peripheral neuropathy with LOPS is present in 78% of diabetic patients with foot ulcers, making it the primary pathophysiologic driver that must be confirmed. 1, 2 While this patient reports "nearly diminished sensation," subjective history alone is insufficient—objective confirmation through the 10-g monofilament test is essential for proper risk stratification and management planning. 2
The American Diabetes Association explicitly states that neurological examination is designed to identify LOPS rather than early neuropathy, making the monofilament test the primary diagnostic tool in this exact clinical scenario. 2 The monofilament test is one of the two most sensitive tests for identifying feet at risk for ulceration. 1, 3
Diagnostic Technique and Interpretation
Perform the 10-g monofilament test at multiple plantar sites, ideally combined with at least one additional neurological assessment (pinprick, temperature perception with 128-Hz tuning fork, or ankle reflexes). 1, 2 Absent monofilament sensation confirms LOPS, while at least two normal tests with no abnormal findings rules it out. 2, 4
The monofilament test demonstrates 100% sensitivity for identifying patients with foot ulcers, making it superior to other screening methods when sensitivity is the critical parameter. 3
Why Other Options Are Less Appropriate
ABI testing (Option A) is indicated for peripheral arterial disease evaluation, not for diagnosing the underlying neuropathic cause of this ulcer. 2 While vascular assessment is important, the clinical presentation (well-demarcated plantar ulcer with diminished sensation and signs of healing) suggests a primarily neuropathic rather than ischemic etiology. ABI should be performed if PAD symptoms or signs are present, but it does not address the fundamental neuropathic pathology. 1
Pressure point assessment (Option D) becomes relevant after confirming LOPS, as part of the treatment strategy involving therapeutic footwear and offloading. 2 However, it is not a diagnostic test—it is a management intervention that follows confirmation of neuropathy.
CT scan (Option C) has no role in initial evaluation unless osteomyelitis is suspected based on clinical findings (deep ulcer, bone exposure, probe-to-bone test). 1 MRI would be the preferred advanced imaging if needed. 1
Impact on Management
Confirming LOPS through monofilament testing fundamentally changes management, requiring specialized therapeutic footwear, pressure redistribution, more frequent monitoring (every 1-3 months for high-risk patients), and referral to foot care specialists. 2, 4 This objective documentation also guides the intensity of patient education and preventive interventions needed to prevent future ulcerations and amputations. 1