What is the diagnostic workup for a patient presenting with bilateral leg numbness?

Diagnostic Workup for Bilateral Leg Numbness

Begin with a focused neuromuscular examination and targeted testing for Guillain-Barré syndrome (GBS), as this is a potentially life-threatening cause requiring prompt diagnosis and treatment. 1

Initial Clinical Assessment

History Taking

• Determine the onset pattern (acute vs. subacute vs. chronic), progression rate, and whether symptoms are constant or intermittent 1
• Ask specifically about preceding infections, vaccinations, or recent travel that may trigger GBS 1
• Assess for exertional patterns: symptoms triggered by walking and relieved by rest suggest peripheral artery disease (PAD), while symptoms relieved by lumbar spine flexion suggest spinal stenosis 2
• Inquire about associated symptoms including weakness, bowel/bladder dysfunction, back pain, or upper extremity involvement 1, 3
• Screen for PAD risk factors if age ≥65 years or age 50-64 with atherosclerosis risk factors 2

Physical Examination

• Perform a comprehensive neurological examination assessing pattern of sensory loss, motor strength in both legs, deep tendon reflexes (particularly knee and ankle jerks), cranial nerve function, and signs of autonomic dysfunction 1
• Conduct a thorough vascular examination including palpation of femoral, popliteal, dorsalis pedis, and posterior tibial pulses bilaterally 4
• Inspect legs and feet for skin changes, ulceration, or signs of ischemia 4
• Assess gait pattern and spine range of motion 2

Diagnostic Testing Algorithm

First-Line Investigations

• Cerebrospinal fluid (CSF) analysis and nerve conduction studies/electromyography (NCS/EMG) are first-line tests when GBS is suspected based on acute/subacute progressive bilateral numbness with areflexia 1
• Ankle-brachial index (ABI) with or without pulse volume recordings should be obtained if vascular claudication is suspected; ABI ≤0.90 confirms PAD 2
• MRI of the cervical and lumbar spine is indicated when spinal cord compression, myelopathy, or spinal stenosis is suspected, particularly if there are upper motor neuron signs, bowel/bladder dysfunction, or back pain 3

Second-Line Testing Based on Initial Results

• If resting ABI is normal or borderline (0.91-1.40) but symptoms suggest PAD, proceed with exercise treadmill ABI test to objectively assess functional limitation 2
• CT angiography or MR angiography of lower extremities if revascularization is being considered for confirmed PAD 4, 2
• Vitamin B12, folate, thyroid function, hemoglobin A1c, and comprehensive metabolic panel to evaluate for metabolic or toxic neuropathies 1

Key Differential Diagnoses to Consider

Peripheral Nervous System Causes

• Guillain-Barré syndrome: Acute onset, ascending pattern, areflexia, preceding infection 1
• Chronic inflammatory demyelinating polyneuropathy (CIDP): Subacute/chronic progressive course 1
• Diabetic or other metabolic neuropathies: Gradual onset, stocking-glove distribution 4

Central Nervous System Causes

• Cervical myelopathy: Can present with isolated lower extremity symptoms without upper extremity involvement, particularly at C6-C7 level 3
• Spinal cord compression: Back pain, bilateral leg weakness, bowel/bladder dysfunction 5
• Lumbar spinal stenosis: Bilateral symptoms relieved by lumbar flexion (shopping cart sign) 2

Vascular Causes

• Peripheral artery disease: Exertional symptoms, diminished pulses, relief with rest 4, 2
• Venous claudication: History of deep vein thrombosis, tight bursting pain, relief with leg elevation 2

Critical Red Flags Requiring Urgent Evaluation

• Acute progressive weakness with areflexia: Hospitalize immediately for GBS monitoring of respiratory function 1
• Bowel/bladder dysfunction with bilateral leg symptoms: Obtain urgent MRI spine to rule out cauda equina syndrome or spinal cord compression 3
• Sudden onset cold, painful leg: Consider acute limb ischemia requiring emergent vascular imaging with CTA or MRA 4

Common Pitfalls to Avoid

• Do not assume lumbar pathology is the cause of bilateral leg numbness without considering cervical myelopathy, as severe cervical stenosis can present with isolated lower extremity symptoms 3
• Do not delay CSF analysis and NCS/EMG if GBS is suspected, as early diagnosis and treatment (within 2 weeks of symptom onset) improves outcomes 1
• Do not rely solely on resting ABI if clinical suspicion for PAD is high but resting ABI is normal; proceed with exercise ABI testing 2
• Bilateral symptoms do not exclude unilateral pathology; asymmetric findings on examination warrant focused imaging of the more affected side 4