What is the initial approach for a patient presenting with lower back pain and unilateral numbness extending into the leg?

Focused Neurological Examination for Lower Back Pain with Unilateral Leg Numbness

Perform a targeted neurological assessment evaluating motor strength, sensory distribution, reflexes, and straight leg raise test to identify radiculopathy, while simultaneously screening for cauda equina syndrome red flags that require immediate intervention. 1

Critical Red Flags Requiring Immediate Assessment

Before proceeding with routine examination, you must first rule out cauda equina syndrome and other emergent conditions:

• Assess for urinary retention (90% sensitivity for cauda equina syndrome) and fecal incontinence—these findings mandate immediate MRI and neurosurgical consultation 1, 2
• Evaluate for saddle anesthesia and bilateral leg weakness, which indicate potential cauda equina syndrome requiring urgent surgical evaluation 3, 1
• Check for progressive neurologic deficits including ascending sensory loss or severe weakness, which necessitate immediate imaging with MRI (preferred) or CT 3, 1

Essential Components of the Focused Neurological Exam

Motor Examination

• Test specific myotomes corresponding to lumbosacral nerve roots:
  • L4: ankle dorsiflexion and knee extension
  • L5: great toe extension and ankle eversion
  • S1: ankle plantarflexion and hip extension 1
• Document any weakness patterns to localize the affected nerve root and determine severity of neurologic compromise 1

Sensory Examination

• Map the dermatomal distribution of numbness or paresthesias:
  • L4: medial leg and foot
  • L5: lateral leg and dorsum of foot
  • S1: lateral foot and heel 1
• Distinguish between radicular patterns (dermatomal) versus non-dermatomal sensory changes, as the latter suggest non-neurologic causes 3

Reflex Testing

• Assess patellar reflex (L4) and Achilles reflex (S1) comparing side-to-side symmetry 1
• Absent or diminished reflexes support radiculopathy at the corresponding level 1

Provocative Testing

• Perform straight leg raise test with the patient supine, raising the affected leg while keeping the knee extended 1
• Positive test reproduces radicular pain radiating below the knee at less than 60 degrees of elevation, indicating nerve root tension from disc herniation 1, 4
• Crossed straight leg raise (pain in affected leg when raising the unaffected leg) is highly specific for disc herniation 4

Additional Examination Elements

• Palpate for midline tenderness, which may indicate vertebral compression fracture (especially with osteoporosis or steroid use) or vertebral infection if accompanied by fever 3, 1
• Observe gait pattern for foot drop, antalgic gait, or inability to walk on heels (L5) or toes (S1) 1

Imaging Decision Algorithm

The neurological examination findings directly determine imaging necessity:

• No imaging needed if examination shows no neurologic deficits and no red flags are present—radiculopathy typically improves within 4 weeks with conservative management 3
• Immediate MRI or CT if severe or progressive neurologic deficits, cauda equina syndrome suspected, or concern for serious underlying condition (cancer, infection, spinal cord compression) 3, 1
• Delayed imaging (after 4-6 weeks) with MRI (preferred) or CT only if persistent radicular symptoms despite conservative therapy AND patient is a potential candidate for surgery or epidural steroid injection 3, 1

Common Pitfalls to Avoid

• Do not order routine imaging for uncomplicated radiculopathy without red flags—this exposes patients to unnecessary radiation, identifies nonspecific abnormalities (bulging discs are common in asymptomatic individuals), and does not improve outcomes 3
• Avoid attributing unilateral numbness to "sciatica" without performing a proper neurological examination to document objective deficits and rule out cauda equina syndrome 1
• Do not miss bilateral symptoms or saddle anesthesia by focusing only on the symptomatic leg—always ask specifically about bowel/bladder function and examine both lower extremities 1, 2
• Recognize that MRI findings (such as bulging disc without nerve root impingement) are often nonspecific and poorly correlated with symptoms—clinical correlation is essential 3