How to diagnose sciatica in a patient from physical examination and medical history?

How to Diagnose Sciatica from Examination

Sciatica is primarily diagnosed through clinical history and physical examination, with the key diagnostic feature being leg pain radiating below the knee in a lumbar nerve root distribution, combined with a focused neurologic examination assessing specific nerve root levels. 1

Clinical History Assessment

The diagnostic process begins with obtaining specific pain characteristics:

• Document the pain distribution pattern: True sciatica presents as pain radiating below the knee into the foot and toes in a typical lumbar nerve root distribution 1, 2
• Assess symptom frequency, duration, and any history of previous episodes and treatment responses 1
• Screen for red flags requiring urgent evaluation: rapidly progressive or severe neurologic deficits, motor deficits at more than one level, fecal incontinence, bladder dysfunction (cauda equina syndrome), or urinary retention (90% sensitivity for cauda equina) 1
• Evaluate for risk factors suggesting alternative diagnoses such as cancer or infection 1

A critical pitfall: Many patients and clinicians use "sciatica" to describe any lower back pain radiating to the leg, but true sciatica specifically involves nerve root compression with pain extending below the knee 3. Referred pain from the lower back without nerve root involvement requires different management.

Physical Examination Maneuvers

Straight Leg Raise (SLR) Test

• The standard SLR test has 91% sensitivity but only 26% specificity for diagnosing herniated disc causing nerve root compression 1, 4
• Perform by flexing the hip with knee extended: A positive test reproduces radiating leg pain between 30-70 degrees of elevation 5
• The crossed SLR test (raising the unaffected leg) is more specific (88%) but less sensitive (29%) for herniated disc 1, 4

Important caveat: The SLR sensitivity decreases significantly with age, dropping below 50% in patients over 60 years old 4. A negative SLR does not rule out sciatica, as the clinical diagnosis can be established through other examination findings.

Focused Neurologic Examination

The neurologic examination should systematically evaluate each nerve root level 1, 4:

• L4 nerve root: Test knee strength and knee reflexes 1
• L5 nerve root: Assess great toe and foot dorsiflexion strength 1
• S1 nerve root: Evaluate foot plantarflexion and ankle reflexes 1
• Sensory examination: Document dermatomal sensory changes, though dermatomes are considered unreliable 6

Distinguishing Piriformis Syndrome

When the SLR test is negative but sciatica symptoms persist, consider piriformis syndrome:

• A negative SLR with positive FAIR test (Flexion, Adduction, Internal Rotation of hip) suggests piriformis syndrome rather than radiculopathy 5, 7
• Piriformis syndrome typically presents with buttocks pain, worse pain with sitting, and normal neurologic examination 7
• Direct palpation of the piriformis muscle reproduces symptoms in piriformis syndrome 7

Diagnostic Categorization

Classify patients into one of three categories: nonspecific low back pain, back pain with radiculopathy or spinal stenosis (sciatica), or back pain with another specific spinal cause 1. This classification guides subsequent management decisions.

Clinical Diagnosis Without Positive SLR

The combination of radicular pain pattern, dermatomal sensory changes, and motor weakness in a nerve root distribution establishes the diagnosis even without positive SLR 4. The clinical definition of sciatica—pain radiating below the knee in sciatic nerve distribution suggesting nerve root compromise—does not require a positive SLR test 4.

When Imaging Is Indicated

MRI is the preferred imaging modality when indicated, as it visualizes soft tissues better, avoids ionizing radiation, and can detect nerve root compression and inflammation 1, 2. However, imaging should be reserved for:

• Patients with red flag symptoms requiring urgent evaluation 1
• Severe or progressive neurological deficits 4
• Persistent sciatica without improvement after 4-6 weeks of conservative management 4

A common pitfall: Images may not correlate with symptoms in approximately 28% of cases 6, so imaging findings must be interpreted in the clinical context.

Psychosocial Considerations

Psychosocial factors are stronger predictors of low back pain outcomes than physical examination findings or pain severity 1. Document the impact on activities of daily living, mood, sleep, and interpersonal relationships as part of the comprehensive assessment 8.