What is the appropriate workup for a patient presenting with tingling in their feet, considering potential neurological or vascular causes, and possible underlying conditions such as diabetes or vitamin deficiencies?

Workup for Tingling in Feet

Begin with a focused history targeting diabetes, vascular symptoms, and medication use, followed by a structured neurological examination using 10-g monofilament testing plus at least one additional sensory test (pinprick, vibration with 128-Hz tuning fork, or temperature), combined with vascular assessment including pedal pulse palpation. 1

Initial History Assessment

Obtain specific information about:

• Neuropathic symptoms: pain, burning, numbness, and the distribution pattern (typically distal and symmetric) 1
• Vascular symptoms: leg fatigue, claudication, rest pain relieved by dependency 2, 3
• Diabetes history: duration of disease, glycemic control status, presence of other microvascular complications (retinopathy, nephropathy) 1
• Risk factors: smoking history, hypertension, dyslipidemia, renal disease 1, 2
• Prior foot complications: ulceration, amputation, Charcot foot, prior vascular procedures 1
• Medication history: particularly metformin use (associated with B12 deficiency), neurotoxic medications 1, 4

Physical Examination Components

Neurological Assessment

The 10-g Semmes-Weinstein monofilament is the primary screening tool and should be combined with at least one additional test. 1, 3

• Monofilament testing: Apply 10-g monofilament to at least 4 sites per foot (can use simplified 8-site total examination which detects 90% of abnormalities compared to 16-site testing), starting at the dorsal aspect of the hallux and moving proximally 1, 3, 5
• Vibration testing: Use 128-Hz tuning fork applied to bony prominences 1, 3
• Pinprick sensation: Assess for small fiber dysfunction 1
• Temperature perception: Can identify small fiber neuropathy 1, 6
• Ankle reflexes: Moderate reproducibility for detecting neuropathy 1, 5

Interpretation: Absent monofilament sensation indicates loss of protective sensation (LOPS); at least two normal tests with no abnormal tests rules out LOPS 1

Vascular Assessment

• Pedal pulse palpation: Dorsalis pedis and posterior tibial arteries 1, 3
• Additional vascular signs: Capillary refill time, rubor on dependency, pallor on elevation, venous filling time 3
• Auscultation: Listen for femoral bruits if vascular disease suspected 2

Dermatological and Structural Assessment

• Skin inspection: Look for ulcerations, pre-ulcerative lesions, calluses, hyperemia, dryness, fungal infections 1, 3
• Foot deformities: Hammertoes, claw toes, bunions, prominent metatarsal heads, Charcot foot, limited joint mobility 7, 3

Laboratory Workup

Essential Tests

• Hemoglobin A1c: Screen for diabetes or assess glycemic control 2
• Vitamin B12 level: Deficiency present in 48% of diabetic neuropathy patients, particularly those >45 years old or with diabetes duration >5 years 4
• Serum creatinine and eGFR: Evaluate for renal insufficiency, a risk factor for neuropathy 2

Additional Testing When Indicated

Consider these when clinical features are atypical or diagnosis unclear: 1

• Thyroid function tests
• Heavy metal screening
• Alcohol use assessment
• Evaluation for chronic inflammatory demyelinating neuropathy
• Vasculitis workup

Advanced Diagnostic Studies

When to Pursue Further Testing

• Ankle-brachial index (ABI): Perform in patients with claudication symptoms, decreased/absent pedal pulses, or other signs of peripheral arterial disease 1, 7
• Toe-brachial index (TBI): Use when ABI >1.40 (suggests non-compressible vessels from medial arterial calcification, common in diabetes and renal disease) 2
• Electrodiagnostic studies: Reserve for atypical presentations, severe neuropathy, or when diagnosis remains unclear after initial workup 1, 8
• Quantitative sensory testing (QST): Has 93% positive predictive value for reduced intraepidermal nerve fiber density when abnormal 6
• Skin biopsy: Detects small fiber neuropathy in 88% of patients with dysesthesias; useful when nerve conduction studies and QST are normal 6

Common Pitfalls to Avoid

• Don't rely on conventional examination alone: Pinprick, position sense, and vibration testing have only fair reproducibility (kappa 0.28-0.36) and correlate poorly with monofilament examination 5
• Don't miss B12 deficiency: Particularly important in patients on metformin, older patients, and those with prolonged diabetes duration 4
• Don't assume normal ABI rules out vascular disease: In diabetic patients with calcified vessels, ABI may be falsely elevated (>1.40); use TBI instead 2
• Don't overlook non-diabetic causes: Consider neurotoxic medications, alcohol abuse, inherited neuropathies, and systemic diseases when presentation is atypical 1

Risk Stratification and Referral

Categorize patients based on examination findings: 7, 3

• Category 0 (very low risk): No LOPS, no peripheral arterial disease
• Category 1 (low risk): LOPS alone
• Category 2 (moderate risk): LOPS with peripheral arterial disease and/or foot deformity
• Category 3 (high risk): LOPS with history of ulcer, amputation, or end-stage renal disease

Refer to specialists when: 1

• Significant claudication or positive ABI requiring vascular assessment
• Smoking history with LOPS or structural abnormalities
• Prior lower-extremity complications
• Severe or atypical neuropathy requiring neurologist evaluation
• Active foot ulcers requiring multidisciplinary care