What is the most helpful diagnostic test for a patient with bilateral leg pain and cramping when walking, along with restricted lumbar spine movement in flexion and extension?

Diagnostic Testing for Bilateral Leg Pain with Lumbar Spine Restriction

The exercise treadmill ankle-brachial index (ABI) test is the most helpful diagnostic test for a patient with bilateral leg pain and cramping when walking more than 2 blocks, with restricted lumbar spine movement and no skin or hair changes. 1

Initial Assessment Algorithm

1. First-line test: Resting ABI

   • Measure systolic blood pressures at arms (brachial arteries) and ankles (dorsalis pedis and posterior tibial arteries) in supine position using Doppler device
   • Calculate ABI by dividing higher ankle pressure by higher arm pressure
   • Interpret results:
     • Abnormal: ≤0.90
     • Borderline: 0.91-0.99
     • Normal: 1.00-1.40
     • Noncompressible: >1.40

2. Based on resting ABI results:

   • If ABI ≤0.90: Confirms PAD diagnosis
   • If ABI is normal (1.00-1.40) or borderline (0.91-0.99): Proceed to exercise treadmill ABI testing
   • If ABI >1.40: Use toe-brachial index (TBI)

Exercise Treadmill ABI Testing

For patients with exertional leg symptoms and normal or borderline resting ABI, exercise treadmill ABI testing is essential to diagnose peripheral artery disease (PAD). This test has a Class I recommendation with Level B-NR evidence 1. The treadmill test typically uses the Strandness protocol (3 km/h speed, 10% slope) and is stopped when the patient cannot walk further due to pain 1.

The exercise treadmill ABI test is particularly valuable because:

• It objectively measures functional limitations
• It can unmask moderate stenosis not detected at rest
• It helps differentiate claudication from pseudoclaudication
• A post-exercise ankle systolic blood pressure decrease >30 mmHg or ABI decrease >20% is diagnostic for PAD

Differential Diagnosis Considerations

The clinical presentation suggests two main diagnostic possibilities:

1. Peripheral Artery Disease (PAD): Bilateral leg pain with cramping when walking suggests claudication
2. Lumbar Spinal Stenosis: Restricted lumbar spine movement suggests possible neurogenic claudication

Key distinguishing features:

• Absence of skin or hair changes makes severe PAD less likely but doesn't rule it out
• Restriction of lumbar spine in flexion and extension points toward possible spinal stenosis

Alternative Tests to Consider

If exercise treadmill ABI is unavailable or inconclusive:

1. For suspected PAD:

   • Segmental pressure measurements with pulse volume recordings
   • Duplex ultrasonography (85-90% sensitivity, >95% specificity for stenosis >50%) 1

2. For suspected lumbar spinal stenosis:

   • MRI of lumbar spine (recommended as neuroimaging study of choice) 1
   • CT myelography (if MRI contraindicated)

Diagnostic Pitfalls to Avoid

1. Don't rely solely on resting ABI when symptoms are primarily exertional - may miss significant PAD
2. Don't assume vascular claudication without exercise testing - neurogenic claudication from spinal stenosis can present similarly
3. Don't overlook mixed disease - patients can have both PAD and lumbar spinal stenosis simultaneously
4. Don't miss non-compressible arteries - in patients with ABI >1.40, use TBI instead

Conclusion

The exercise treadmill ABI test provides the most valuable diagnostic information for this clinical presentation by:

• Objectively documenting the relationship between exercise and symptoms
• Differentiating vascular from neurogenic claudication
• Establishing a baseline for treatment response monitoring
• Providing functional assessment of symptom limitations

If the exercise treadmill ABI is normal, further evaluation with lumbar spine MRI would be appropriate to assess for spinal stenosis as an alternative cause of symptoms.