What is the appropriate workup and treatment for a patient, particularly an older patient with a history of diabetes, presenting with foot numbness, potentially indicating peripheral neuropathy or peripheral artery disease?

Workup for Foot Numbness in Diabetic Patients

For a diabetic patient presenting with foot numbness, perform a comprehensive foot examination including 10-g monofilament testing plus at least one additional neurological test (pinprick, temperature, vibration with 128-Hz tuning fork, or ankle reflexes), along with vascular assessment including pedal pulse palpation and evaluation for peripheral arterial disease. 1

Initial Clinical Assessment

History Taking

Obtain specific information about:

• Prior ulceration, amputation, or Charcot foot 1
• Vascular history: angioplasty, vascular surgery, symptoms of claudication (leg fatigue with walking), or rest pain 1
• Smoking status - a critical modifiable risk factor 1
• Other microvascular complications: retinopathy and chronic kidney disease (especially dialysis patients) 1
• Current neuropathic symptoms: pain, burning sensations, or numbness 1

Physical Examination Components

Neurological Assessment (to identify loss of protective sensation):

• 10-g Semmes-Weinstein monofilament testing - the single most useful screening tool 1, 2
• Plus at least one additional test: pinprick sensation (dorsum of foot), temperature perception, vibration with 128-Hz tuning fork, or ankle reflexes 1
• Interpretation: Absent monofilament sensation suggests loss of protective sensation; at least two normal tests with no abnormal tests rules it out 1, 2

Vascular Assessment:

• Palpate dorsalis pedis and posterior tibial pulses 1
• Assess capillary refill time, rubor on dependency, pallor on elevation, and venous filling time 1, 2
• If claudication symptoms or decreased/absent pulses are present: refer for ankle-brachial index (ABI) testing 1, 2
• Note: In diabetic patients or those with renal insufficiency who have ABI >1.40 (falsely elevated due to calcified vessels), obtain toe-brachial index instead 2

Skin and Structural Assessment:

• Inspect for: calluses, color changes, temperature differences, edema, pre-ulcerative signs 1
• Assess for foot deformities: hammertoes, claw toes, prominent metatarsal heads, bunions, Charcot foot 1
• Evaluate footwear: inspect both inside and outside of shoes and socks 1

Laboratory Workup

Essential initial tests:

• HbA1c - to assess glycemic control, as optimal control can prevent and slow neuropathy progression 1, 2
• Serum creatinine and estimated glomerular filtration rate (eGFR) - renal insufficiency increases neuropathy and foot complication risk 2

Additional testing if neuropathy is atypical or diagnosis uncertain 3:

• Complete blood count
• Comprehensive metabolic profile
• Fasting blood glucose (if not already diabetic)
• Vitamin B12 level
• Thyroid-stimulating hormone
• Serum protein electrophoresis with immunofixation

When to consider electrodiagnostic studies: Reserve for atypical presentations or when clinical features don't fit typical diabetic peripheral neuropathy 1, 3

Risk Stratification and Follow-up Frequency

Based on the International Working Group on the Diabetic Foot classification 1:

• Category 0 (no neuropathy): Annual screening 1
• Category 1 (peripheral neuropathy present): Every 6 months 1
• Category 2 (neuropathy + PAD and/or foot deformity): Every 3-6 months 1
• Category 3 (neuropathy + history of ulcer/amputation): Every 1-3 months 1

Patients with evidence of sensory loss or prior ulceration should have feet inspected at every visit 1

Referral Indications

Immediate referral to foot care specialist for:

• History of prior lower-extremity ulcers or amputations 1
• Loss of protective sensation with structural abnormalities 1
• Peripheral arterial disease 1
• Active smoking with any of the above risk factors 1

Vascular surgery referral for:

• Symptoms of claudication or rest pain 1
• Decreased or absent pedal pulses 1
• Abnormal ABI 1, 2

Neurology referral: Only when clinical features are atypical or suggest non-diabetic etiology 1, 3

Critical Pitfalls to Avoid

• Don't assume all foot numbness in diabetics is from peripheral neuropathy - up to 25-46% of peripheral neuropathy cases are idiopathic, and other treatable causes must be excluded 3
• Don't miss peripheral arterial disease - up to 50% of diabetic foot ulcer patients have PAD, and many are asymptomatic due to neuropathy 1, 4
• Don't rely on symptoms alone - up to 50% of diabetic peripheral neuropathy is asymptomatic, requiring objective testing 1
• Don't overlook the acute red, hot, swollen foot - this requires immediate workup to exclude Charcot neuroarthropathy 1
• Neuropathy screening identifies high-risk patients - those with both neuropathy and PAD have significantly increased risk of amputation, revascularization, and death (hazard ratio 3.19) 4