What is the most likely diagnosis and appropriate management for a patient with low back pain radiating down the entire left leg and a CT scan showing no significant abnormalities?

Lumbar Radiculopathy (Sciatica) with Normal CT Imaging

This patient has lumbar radiculopathy (sciatica) requiring MRI of the lumbar spine without contrast to identify the underlying cause, as CT imaging is inadequate for visualizing nerve root compression from disc herniation or other soft tissue pathology. 1, 2

Diagnosis

The most likely diagnosis is lumbar radiculopathy caused by disc herniation or other soft tissue pathology that is not visible on CT. 1, 2

• Radicular pain radiating down the entire left leg in a dermatomal distribution is the hallmark of lumbosacral radiculopathy, with annual prevalence ranging from 9.9% to 25% in the general population 3
• CT without contrast has limited soft tissue resolution and cannot adequately visualize intervertebral discs, the thecal sac, or neural structures that are typically responsible for radicular symptoms 1, 2
• While CT demonstrates >80% sensitivity for canal and foraminal stenosis, it is inferior to MRI for detecting disc herniations and nerve root compression 2

Immediate Management Steps

Order MRI lumbar spine without IV contrast as the definitive diagnostic study. 1, 2

• MRI provides superior soft-tissue contrast and accurately depicts disc degeneration, thecal sac morphology, and neural structures causing radiculopathy 1
• MRI is the gold standard because it avoids ionizing radiation and offers better visualization of vertebral marrow and the spinal canal compared to CT 2
• The American College of Radiology designates MRI without contrast as the preferred initial imaging modality for suspected nerve root compression causing radicular symptoms 2

Determine if immediate MRI is warranted or if conservative management should precede imaging: 1, 2

• Obtain immediate MRI (no waiting period) if any of the following red flags are present:

  • Progressive or severe neurological deficits (motor weakness worsening over days)
  • Suspected cauda equina syndrome (urinary retention/incontinence, saddle anesthesia, bilateral leg weakness)
  • Clinical suspicion of malignancy, infection, or vertebral fracture
  • 1, 2

• If no red flags are present and neurological exam is normal or stable, initiate 6 weeks of conservative management before obtaining MRI 1, 2

  • The natural history shows improvement within the first 4 weeks in the majority of patients with disc herniation and radiculopathy 2
  • MRI should only be obtained after failed conservative therapy and only if the patient is a potential candidate for surgery or epidural steroid injection 2

Conservative Treatment Protocol (If No Red Flags)

Implement the following evidence-based conservative treatments for 6 weeks: 4

• Patient education and self-management (moderate evidence, Level B) 4
• McKenzie method (moderate evidence, Level B) 4
• Exercise therapy and mobilization (moderate evidence, Level B) 4
• Neural mobilization techniques (moderate evidence, Level B) 4
• Consider epidural steroid injections if symptoms persist beyond 6 weeks and patient is not a surgical candidate (moderate evidence, Level B) 4

Surgical Referral Criteria

Refer to spine surgery if the following conditions are met: 1, 5

• Radicular symptoms persisting >6 weeks despite conservative management 2
• MRI demonstrates nerve root compression that correlates with clinical symptoms and neurological deficits 5
• Objective neurological deficits present (motor weakness, reflex loss) that correspond to the affected nerve root 5
• Patient is medically appropriate for surgical intervention 5

The American College of Physicians suggests considering referral after a minimum of 3 months of failed nonsurgical interventions for nonspecific low back pain, though patients with clear radiculopathy and corresponding imaging findings may be referred earlier. 1

Critical Pitfalls to Avoid

Do not rely on CT imaging alone to exclude significant pathology in patients with radicular symptoms. 1, 2

• CT has insufficient soft tissue contrast to visualize most disc herniations and nerve root compression 1
• Up to 20-28% of asymptomatic individuals have disc herniations on MRI, so imaging must correlate with clinical findings 2

Do not obtain MRI for acute low back pain without radiculopathy or red flags. 2

• Routine imaging for nonspecific low back pain does not improve outcomes and may lead to unnecessary interventions 2

Do not proceed with invasive interventions without clear correlation between clinical symptoms, neurological findings, and imaging results. 2, 5

• Therapeutic decisions must integrate symptom severity, imaging correlation, patient preferences, and surgical risks 2