What is the workup for a patient presenting with lower leg pain, considering their age, medical history, and lifestyle?

Workup for Lower Leg Pain

Begin with a focused vascular history and physical examination, followed by resting ankle-brachial index (ABI) measurement as the initial diagnostic test to establish or exclude peripheral artery disease (PAD), which is the most critical life-threatening cause of lower leg pain. 1

Initial Clinical Assessment

Characterize the Pain Pattern

• Determine if pain occurs predictably with walking a certain distance and resolves within 10 minutes of rest, which indicates vascular claudication 1
• Assess for critical limb ischemia features: rest pain (especially at night), non-healing wounds, ulcers, or tissue loss—these are vascular emergencies 2, 1
• Document if pain radiates in a typical lumbar nerve root distribution (L4/L5 or L5/S1), suggesting sciatica from herniated disc 2
• Identify if pain improves with sitting or worsens with downhill walking, which suggests lumbar spinal stenosis 2

Risk Factor Assessment

• Document atherosclerotic risk factors: age ≥65 years, age ≥50 years with smoking or diabetes history, hypertension, hyperlipidemia 2, 1
• Screen for history of coronary artery disease, carotid disease, or renal artery disease—these patients have high PAD prevalence 2, 1
• Assess for inflammatory back pain features: age <40 years, morning stiffness >30 minutes, improvement with exercise, alternating buttock pain, awakening during second part of night 2

Physical Examination Priorities

• Perform comprehensive lower extremity pulse examination (femoral, popliteal, dorsalis pedis, posterior tibial) 2, 1
• Conduct straight-leg-raise test (positive if reproduces sciatica between 30-70 degrees of leg elevation; sensitivity 91%, specificity 26%) 2
• Perform crossed straight-leg-raise test (more specific at 88% but less sensitive at 29%) 2
• Test knee strength and reflexes (L4), great toe/foot dorsiflexion strength (L5), foot plantarflexion and ankle reflexes (S1) 2

Diagnostic Testing Algorithm

First-Line Testing

• Obtain resting ABI with or without segmental pressures in all patients with suspected PAD based on history, risk factors, or abnormal pulse examination 2, 1
• Interpret ABI: ≤0.90 = PAD confirmed, 0.91-0.99 = borderline, 1.00-1.40 = normal, >1.40 = noncompressible arteries 1
• If ABI >1.40 (noncompressible), proceed immediately to toe-brachial index (TBI)—this is critical in diabetic patients and those with chronic kidney disease 1

Exercise Testing Indications

• If ABI is normal or borderline (0.91-1.40) but exertional leg symptoms persist, perform exercise treadmill ABI testing to diagnose PAD 2, 1
• If ABI is abnormal (≤0.90) and patient has claudication, consider exercise treadmill ABI to objectively quantify functional limitation 1
• Alternative: 6-minute walk test for elderly patients or those unable to perform treadmill testing 2

When to Image

• Do not obtain anatomic imaging (duplex ultrasound, CTA, MRA) unless revascularization is being considered 1
• For symptomatic PAD patients being considered for revascularization: duplex ultrasound is first-line for anatomic localization and stenosis severity 2, 1
• For critical limb ischemia patients being considered for revascularization: invasive angiography is the recommended modality 1

Differential Diagnosis Considerations

Vascular Causes (Highest Priority)

• PAD with claudication: 62% have atypical leg pain, only 13% have classic claudication 2
• Critical limb ischemia: requires immediate vascular specialist evaluation 2, 1
• Acute limb ischemia: vascular emergency requiring emergent anatomic definition and revascularization 2

Neurogenic Causes

• Lumbar disc herniation with sciatica: >90% occur at L4/L5 or L5/S1 levels 2
• Lumbar spinal stenosis: age >65 years has positive likelihood ratio of 2.5 2
• Peripheral nerve entrapment: consider in athletes with chronic leg pain 3

Musculoskeletal Causes (in Athletes)

• Medial tibial stress syndrome (most frequent in athletes) 3
• Chronic exertional compartment syndrome: requires intramuscular pressure recordings for diagnosis 3, 4
• Stress fracture 3

Critical Clinical Pitfalls

• Patients with diabetes and critical limb ischemia may have no pain due to neuropathy but still have severe tissue loss requiring urgent evaluation 1
• Never rely on ABI alone in diabetic patients—obtain TBI due to high incidence of noncompressible arteries 1
• Patients at risk for CLI who develop acute limb symptoms represent vascular emergencies and require immediate vascular specialist assessment 1
• PAD is 2-5 times more prevalent than symptomatic claudication suggests; most patients are "asymptomatic" but have measurable limb dysfunction 2
• Do not routinely obtain imaging for nonspecific low back pain without red flag features 2