What are the typical presentation and causes of sciatic nerve pain?

Sciatic Nerve Pain: Presentation and Causes

Definition and Core Presentation

Sciatica is pain radiating down the leg below the knee in the distribution of the sciatic nerve, caused by nerve root compromise from mechanical pressure or inflammation, most commonly from lumbar disc herniation at L4/L5 or L5/S1 levels. 1, 2

Typical Clinical Presentation

Pain Characteristics

• Radiating pain extending below the knee into the foot and toes in the sciatic nerve distribution (posterior thigh, lateral or posterior leg) 2, 3
• Neuropathic quality: burning, electric sensation, or dysesthesia 2
• Aggravated by spinal flexion/extension, walking, or running 2
• Pain may vary with body position and activities that stretch or compress the affected nerve root 2

Neurological Findings by Nerve Root Level

• L4 involvement: Sensory deficits in L4 dermatome, knee weakness, diminished patellar reflex 2
• L5 involvement: Sensory deficits in L5 dermatome, great toe and foot dorsiflexion weakness 2
• S1 involvement: Sensory deficits in S1 dermatome, foot plantarflexion weakness, diminished or absent ankle reflex 2

Physical Examination Findings

• Straight-leg-raise test: 91% sensitivity but only 26% specificity for herniated disc (positive when leg raised 30-70 degrees reproduces sciatic pain) 1, 2, 4
• Crossed straight-leg-raise test: 29% sensitivity but 88% specificity (pain when raising the unaffected leg) 2, 4

Common Causes

Mechanical Causes (Most Common)

• Lumbar disc herniation: Over 90% of symptomatic herniations occur at L4/L5 and L5/S1 levels, accounting for the vast majority of sciatica cases 2, 3
• Spinal stenosis: Narrowing of spinal canal causing neurogenic claudication (pain with walking/standing, relieved by sitting or spinal flexion) 1, 2
• Posterior intervertebral osteoarthritis 5

Less Common Causes

• Piriformis syndrome: Compression as nerve exits pelvis through greater sciatic foramen (nerve passes below piriformis in 92.5% of cases) 2, 6
• Pelvic tumoral infiltration causing truncular sciatica 5
• Inflammatory processes around disc and nerve root 5
• Peripheral nerve compression: External popliteal nerve at fibular neck, tarsal tunnel syndrome 5

Red Flag Symptoms Requiring Urgent Evaluation

Immediately evaluate for cauda equina syndrome if any of the following are present:

• Urinary retention (90% sensitivity for cauda equina syndrome) 2
• Fecal incontinence 2
• Saddle anesthesia 1
• Bilateral motor weakness of lower extremities 1
• Rapidly progressive or severe neurological deficits 2

Clinical Course and Prognosis

• Most acute sciatica improves within 2-4 weeks with or without treatment 3
• Psychosocial factors and emotional distress are stronger predictors of outcomes than physical examination findings or pain severity 2

Diagnostic Approach

When to Image

• Immediate MRI indicated for: Severe or progressive neurological deficits, red flag symptoms suggesting cauda equina syndrome or other serious pathology 4
• Delayed imaging (4-6 weeks) appropriate for: Persistent sciatica without improvement despite conservative management 4
• MRI is preferred modality: Better soft tissue visualization than CT, no ionizing radiation 3

Clinical Pitfalls

• Disc herniation visualized on imaging does not fully account for pain; inflammatory processes play important roles 5
• Extraspinal causes are frequently underestimated—don't stop evaluation after reviewing lumbar spine imaging if clinical picture doesn't fit 7
• Degenerative changes on imaging correlate poorly with symptoms and are considered nonspecific 1