What is the appropriate next step in management and investigation for a 35-year-old woman with acute severe low back pain radiating to the left leg after a popping sound during leg‑press exercise and a normal plain‑film X‑ray?

Immediate Management: Order MRI Lumbar Spine Without Contrast Now

This patient has acute lumbar radiculopathy with clear red-flag features—specifically, severe debilitating pain requiring walking aids and a mechanical injury with an audible "pop"—that warrant immediate advanced imaging without waiting for a 6-week conservative trial. 1

Why MRI Is Indicated Immediately

Your patient meets multiple criteria for urgent imaging:

• Severe neurological symptoms causing significant functional disability (requiring walking sticks, pain radiating from lower back through left buttock to toes) constitute a red-flag presentation that bypasses the usual 6-week waiting period. 1, 2
• Acute traumatic mechanism with audible "pop" during leg press suggests acute disc herniation with possible nerve root compression requiring prompt diagnosis. 1
• MRI lumbar spine without IV contrast is the gold-standard imaging modality because it accurately depicts soft-tissue pathology, disc herniation, nerve root compression, and spinal canal patency—none of which are visible on plain X-rays. 3, 1, 4
• The American College of Radiology specifically recommends immediate MRI for severe symptoms or significant neurological findings at initial presentation, rather than waiting 4–6 weeks. 1, 2

Critical Red Flags to Assess Immediately

Before ordering the MRI, you must screen for cauda equina syndrome:

• Ask specifically about urinary retention (90% sensitivity for cauda equina), fecal incontinence, and saddle anesthesia. 1
• If any of these are present, this is a surgical emergency—arrange same-day MRI and immediate neurosurgical consultation. 1
• Assess for progressive motor weakness, which also mandates urgent imaging and referral. 1

Physical Examination Priorities

Document these specific findings to support your MRI request and guide management:

• Straight-leg raise test (91% sensitivity for disc herniation, though only 26% specificity). 1
• Crossed straight-leg raise (more specific at 88%, but less sensitive at 29%). 1
• Neurological examination: Test L5/S1 distribution specifically—ankle dorsiflexion and plantarflexion strength, ankle reflexes, great toe dorsiflexion, and sensory distribution along the lateral leg and foot. 1
• Document any motor weakness objectively (e.g., 4/5 strength) as this strengthens the case for imaging and potential surgical referral. 1

Initial Pharmacologic Management (Start Today)

While arranging the MRI, initiate conservative therapy:

• NSAIDs are first-line with good evidence for moderate pain relief in acute radicular pain. 1
• Add a skeletal muscle relaxant for short-term use (good evidence for acute low back pain). 1
• Superficial heat has good evidence for moderate benefit. 1
• Avoid opioids as first-line; reserve for lowest dose/shortest duration only if NSAIDs insufficient. 1

Non-Pharmacologic Interventions

• Advise the patient to remain as active as tolerated—bed rest is contraindicated and worsens outcomes. 1
• Reassure about favorable prognosis: Most patients with disc herniation improve within 4 weeks, and the majority of disc herniations show radiographic regression by 8 weeks. 3, 1
• Consider referral for spinal manipulation (fair evidence for small-to-moderate benefits in acute presentations). 1

What NOT to Do

• Do not order epidural steroid injections at this stage. The most recent BMJ guideline provides a strong recommendation AGAINST epidural injection of local anesthetic, steroids, or their combination for radicular spine pain. 1
• Do not delay imaging waiting for "6 weeks of conservative therapy" when severe functional disability is present—this patient's inability to walk without aids constitutes a severe presentation. 1, 2
• Do not order CT scan as first-line imaging—it lacks adequate soft-tissue resolution to visualize disc herniation and nerve root compression. 4

Insurance Documentation

To ensure MRI approval, document:

• Specific radicular symptoms: Pain radiating from lower back through left buttock to toes in L5/S1 distribution. 4
• Neurological findings: Results of straight-leg raise, motor strength testing, reflex examination, and sensory distribution. 4
• Severity and functional impact: Requiring walking aids, debilitating pain preventing normal activities. 4
• Mechanism of injury: Acute traumatic event (leg press with audible "pop") suggesting acute disc herniation. 4
• Rationale for imaging: Patient is potential candidate for surgical intervention or epidural injection if conservative management fails. 4

Surgical Referral Pathway

• If MRI confirms nerve root compression correlating with clinical findings and symptoms persist beyond 6 weeks of appropriate conservative therapy, refer to spine surgery. 1
• The American College of Physicians recommends at least 6 weeks of conservative therapy before considering surgery for lumbar disc herniation with radiculopathy (unless progressive motor weakness or cauda equina develops). 1
• Earlier specialist referral (within 2 weeks) is appropriate for severe radicular pain that is disabling and prevents normal daily activities—which this patient has. 1

Common Pitfalls

• Waiting 6 weeks for imaging in a severely disabled patient: The guideline exception for "severe symptoms at initial presentation" applies here. 1, 2
• Accepting normal X-ray as reassurance: Plain films cannot visualize disc herniation, nerve root compression, or soft-tissue pathology. 3, 4
• Rushing to interventional procedures: Epidural injections are not recommended based on current high-quality evidence. 1