What is the appropriate workup for a patient with partial numbness of the left lateral foot and heel?

Workup for Partial Numbness of Left Lateral Foot and Heel

The appropriate workup should prioritize ruling out peripheral neuropathy (particularly diabetic) and peripheral arterial disease through focused history, targeted physical examination, and selective laboratory testing, with imaging reserved only for specific red flags. 1

Initial Clinical Assessment

History taking should focus on:

• Duration and pattern of symptoms—whether constant versus intermittent, and whether symptoms worsen with activity or at night 1
• Specific characteristics: burning sensations, sharp pain, or purely sensory changes to assess small fiber involvement 1
• Risk factors for systemic neuropathy: diabetes history, alcohol use, vitamin B12 deficiency, family history of neuropathy, medications, and autoimmune conditions 1
• Vascular symptoms: leg fatigue, claudication, or pain with exertion that suggests peripheral arterial disease 2
• History of foot ulcers, amputation, or prior vascular interventions 2

The lateral foot and heel distribution (S1 dermatome) suggests possible S1 radiculopathy, but the unilateral presentation makes systemic causes like diabetic neuropathy less likely initially 3. However, bilateral presentation would strongly suggest systemic disease rather than focal compression 1.

Physical Examination

Perform a comprehensive neurological foot examination including:

Small Fiber Function

• Pinprick sensation testing in the lateral foot and heel 1
• Temperature sensation testing 1

Large Fiber Function

• Vibration testing with 128-Hz tuning fork 1
• Assessment of ankle reflexes (particularly Achilles reflex for S1) 1

Protective Sensation

• 10-g monofilament testing at multiple plantar sites—this is the single most important test for ulcer risk stratification 1

Vascular Assessment

• Palpation of dorsalis pedis and posterior tibial pulses bilaterally 4
• Assessment of capillary refill time 4
• Check for rubor on dependency and pallor on elevation 4
• If diminished or absent pedal pulses are found, obtain ankle-brachial index (ABI) immediately 5

Structural Examination

• Inspection for foot deformities, calluses, or skin changes 2

Laboratory Workup

Order the following initial tests:

• Hemoglobin A1c or fasting glucose to screen for diabetes—the most common cause of peripheral neuropathy 1
• Vitamin B12 level, as deficiency causes sensory neuropathy 1
• Thyroid function tests, as hypothyroidism causes neuropathy 1
• Complete blood count to screen for anemia or hematologic disorders 1
• Comprehensive metabolic panel to assess renal function and electrolytes 1

Imaging Considerations

Imaging is NOT routinely indicated for this presentation unless specific red flags are present 1. Do NOT order routine foot radiographs unless there is:

• History of trauma 1
• Inability to bear weight 1
• Point tenderness over bony structures per Ottawa Ankle Rules 1

This is a critical pitfall to avoid—extensive imaging initially is low-yield and not indicated, as this is a clinical diagnosis 1.

Electrodiagnostic Testing

Electrophysiological testing (EMG/NCS) is rarely needed initially 1. Reserve electrodiagnostic studies for:

• Cases where clinical features are atypical 1
• Diagnosis remains unclear after initial workup 1
• Symptoms persist beyond 6-8 weeks despite conservative management 1

Clinical Decision Algorithm

If laboratory tests show abnormalities:

• Treat underlying conditions: diabetes management, vitamin B12 supplementation, thyroid replacement 1
• Optimize glycemic control aggressively if diabetic, as this is the only intervention that can prevent DPN progression 4

If ABI ≤0.90 (confirming PAD):

• Initiate antiplatelet therapy 5
• Aggressive risk factor modification 5
• Refer to vascular surgery for consideration of revascularization 5

If symptoms persist beyond 6-8 weeks:

• Refer to neurology for electrodiagnostic studies 1
• Consider podiatry referral for custom orthotics and biomechanical assessment 1

If loss of protective sensation on monofilament testing:

• Refer to podiatry for ongoing preventive care and lifelong surveillance 2
• Implement comprehensive foot care education 2

Critical Pitfalls to Avoid

• Do not assume symptoms are purely mechanical without screening for diabetes, even in younger adults 1
• Be cautious with unilateral presentation—while it may suggest focal compression (S1 radiculopathy), still screen for systemic disease 1, 3
• Do not order extensive imaging initially without red flags 1
• Do not miss peripheral arterial disease—up to 24% of diabetic patients aged 55-74 have diminished pedal pulses 4