What are the initial investigations and physical exam for a patient presenting with lumbar nerve root irritation?

Physical Examination and Initial Investigations for Lumbar Nerve Root Irritation

Physical Examination

Perform a focused neurological examination targeting specific nerve root levels (L4, L5, S1) with straight-leg raise testing to assess for radiculopathy. 1

Nerve Root-Specific Testing

• L4 nerve root: Test knee extension strength and patellar reflexes 1
• L5 nerve root: Assess great toe and foot dorsiflexion strength 1
• S1 nerve root: Evaluate foot plantarflexion strength and ankle reflexes 1
• Sensory distribution: Map the pattern of sensory symptoms along the affected dermatome 1

Provocative Testing

• Straight-leg raise test: Positive when sciatica is reproduced between 30-70 degrees of leg elevation, with 91% sensitivity but only 26% specificity for herniated disc 1
• Crossed straight-leg raise test: More specific (88%) but less sensitive (29%) than standard straight-leg raise 1

Red Flag Assessment

Screen for serious underlying pathology requiring urgent imaging:

• Cauda equina syndrome: Urinary retention (90% sensitivity), fecal incontinence, saddle anesthesia, bilateral leg weakness 1
• Cancer risk factors: History of cancer (increases probability from 0.7% to 9%), unexplained weight loss, age >50 years, failure to improve after 1 month 1
• Infection indicators: Fever, intravenous drug use, recent infection 1
• Fracture risk: Older age, osteoporosis history, corticosteroid use 1
• Progressive neurological deficits: Motor deficits at multiple levels, rapidly worsening symptoms 1

Initial Investigations

When Imaging is NOT Indicated

Do not order imaging for acute low back pain with radicular symptoms in the absence of red flags during the first 6 weeks, as most cases resolve with conservative treatment. 1, 2

• Routine imaging does not improve outcomes and may lead to unnecessary interventions 2
• MRI findings correlate poorly with symptoms—20-28% of asymptomatic individuals have disc herniations 2

When Imaging IS Indicated

Order MRI lumbar spine without contrast as the first-line imaging modality when:

• Radicular symptoms persist ≥6 weeks despite conservative management AND patient is a surgical or epidural steroid injection candidate 2
• Any red flag symptoms are present (cauda equina, progressive neurological deficits, suspected cancer/infection) 1, 2
• Severe or progressive neurological deficits develop at any time 2

MRI Protocol

• MRI lumbar spine without IV contrast is the preferred initial imaging modality for suspected nerve root compression 1, 2
• MRI accurately identifies disc herniation, nerve root compression, spinal stenosis, and soft tissue pathology 1
• MRI with and without contrast is reserved for postoperative patients to distinguish recurrent disc herniation from scar tissue 1

Alternative Imaging

CT myelography lumbar spine is appropriate when:

• Patient has contraindications to MRI (pacemaker, certain implants) 1
• Significant metallic artifact from surgical hardware degrades MRI quality 1
• Occasionally more accurate for diagnosing lateral recess nerve root compression 1
• Disadvantage: requires lumbar puncture with intrathecal contrast injection 1

Plain radiographs have limited utility:

• May show spondylosis, degenerative disc disease, or alignment issues but rarely alter initial management 1
• More useful for evaluating hardware integrity in postoperative patients 1

Common Pitfalls

• Avoid imaging asymptomatic findings: Up to 28% of asymptomatic individuals have disc herniations on MRI that do not correlate with clinical symptoms 2
• Do not rely solely on straight-leg raise: While sensitive (91%), it has poor specificity (26%) and must be interpreted with neurological examination findings 1
• Document appropriately for insurance: Specify radicular symptoms, neurological findings, duration, failed conservative treatments, and rationale for surgical/interventional consideration 2
• Recognize that >90% of symptomatic disc herniations occur at L4/L5 and L5/S1 levels: Focus examination on these nerve roots 1