What is the diagnostic approach for a patient presenting with right-sided sciatica, particularly in terms of clinical examination, imaging, and management?

How to Test for Sciatica

The diagnosis of sciatica is primarily clinical, based on history and physical examination, with the straight-leg-raise test being the key diagnostic maneuver; imaging with MRI should be reserved for patients with red flags, severe progressive neurological deficits, or symptoms persisting beyond 6-8 weeks of conservative treatment. 1, 2, 3

Clinical History Assessment

The diagnostic approach begins with specific historical features that distinguish true radiculopathy from referred pain:

• Pain distribution: Leg pain radiating below the knee into the foot and toes in a dermatomal pattern (L4, L5, or S1 distribution) has high sensitivity for disc herniation 2, 4
• Duration and frequency: Document symptom duration, previous episodes, and prior treatment responses 2, 3
• Red flag screening: Assess for cancer risk factors, infection signs (fever, IV drug use, immunosuppression), progressive neurological deficits, bowel/bladder dysfunction, or saddle anesthesia 1, 2, 3

Physical Examination Maneuvers

Primary Tests

• Straight-leg-raise (Lasègue) test: Flex the hip with knee extended between 30-70 degrees; reproduction of leg pain indicates nerve root tension with 91% sensitivity but only 26% specificity for disc herniation 1, 2, 3
• Crossed straight-leg-raise test: Pain reproduction when lifting the unaffected leg is more specific (88%) but less sensitive (29%) for disc herniation 1, 2, 3

Supplementary Stretching Tests

When the Lasègue test is equivocal, additional maneuvers improve diagnostic accuracy:

• Bragard test: Passive ankle dorsiflexion at the end of straight-leg-raise increases sensitivity 5
• Slump test: Performed sitting, slowly extend the painful leg then passively flex the neck to reproduce symptoms 5
• Bowstring test: At the end of Lasègue test, slightly flex the knee and press on the peroneal/tibial nerves in the popliteal fossa to reproduce exact pain 5

These combined tests take less than 2 minutes and improve both sensitivity and specificity beyond the Lasègue test alone. 5

Neurological Examination

Perform focused testing of specific nerve roots:

• L4 root: Knee extension strength and patellar reflex 2, 3
• L5 root: Great toe and foot dorsiflexion strength 2, 3
• S1 root: Foot plantarflexion strength and ankle reflex 2, 3

Urgent Red Flags Requiring Immediate MRI

Obtain emergent MRI if any of the following are present:

• Rapidly progressive or severe neurological deficits 2, 3
• Motor deficits at more than one level 2, 3
• Fecal incontinence or bladder dysfunction (cauda equina syndrome) 2, 3
• Urinary retention (90% sensitive for cauda equina syndrome) 2, 3

Imaging Strategy

When NOT to Image

• No immediate imaging for acute sciatica without red flags 3, 4
• The clinical course is generally favorable, with most symptoms improving within 2-4 weeks 4

When to Obtain MRI

MRI is the preferred imaging modality when indicated because it visualizes soft tissues better than CT, detects nerve root compression and inflammation, and avoids ionizing radiation. 2, 3, 4

Timing for MRI:

• After 6-8 weeks of conservative treatment if symptoms persist without improvement 3, 4
• Immediately if red flags are present 2, 3
• When considering surgical intervention 1

Alternative Imaging Considerations

• Radiographs: Not useful for typical sciatica from disc herniation, as they cannot visualize soft tissues 1
• CT: Inferior to MRI for soft tissue evaluation; reserve for patients who cannot undergo MRI 4

Differential Diagnosis Considerations

Piriformis Syndrome

When sciatica symptoms are present but imaging is normal:

• Buttocks pain worse with sitting 6
• Normal neurological examination and negative straight-leg-raise 6
• Pain with flexion, adduction, and internal rotation of hip (Freiberg sign) 6
• Pain with direct palpation of piriformis muscle 6

Inflammatory Sacroiliitis

If inflammatory back symptoms suggest axial spondyloarthropathy rather than mechanical sciatica:

• Start with radiographs of sacroiliac joints and spine (not MRI) 1, 3
• If radiographs are negative or equivocal, proceed to MRI of sacroiliac joints without contrast 1, 3

Critical Clinical Pitfalls

• Psychosocial factors are stronger predictors of outcomes than physical examination findings or pain severity 2
• A negative Lasègue test does not exclude sciatica—the combination of radicular pain, dermatomal sensory changes, and motor weakness establishes diagnosis even without positive straight-leg-raise 3
• Dermatomes are unreliable for precise localization 7
• Imaging abnormalities may not correlate with symptoms in approximately 28% of cases 7
• Avoid the term "sciatica" for any leg pain—reserve it specifically for radicular pain from nerve root compression, not referred pain from the lower back 8