Sciatica

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Sciatica refers to pain radiating along the sciatic nerve, typically from the lower back down the leg. It is commonly caused by nerve compression, irritation, or inflammation, leading to unilateral leg pain that follows a dermatomal distribution.

Aetiology

Sciatica is primarily caused by conditions that compress or irritate the sciatic nerve.

1. Mechanical Causes:

  • Herniated disc: protrusion of the intervertebral disc compresses the sciatic nerve.
  • Spinal stenosis: narrowing of the spinal canal compresses the nerve roots.
  • Spondylolisthesis: vertebral slippage causing nerve root compression.
  • Degenerative disc disease: disc degeneration leading to nerve irritation.

2. Non-Mechanical Causes:

  • Piriformis syndrome: compression of the sciatic nerve by the piriformis muscle.
  • Trauma: pelvic fractures or direct injury to the nerve.
  • Tumours: spinal or pelvic tumours pressing on the sciatic nerve.
  • Infections: epidural abscesses or osteomyelitis causing nerve compression.

Pathophysiology

  • Compression or irritation of the sciatic nerve leads to inflammation and pain along its distribution.
  • The nerve originates from the L4-S3 spinal roots and supplies the posterior thigh and lower leg.
  • Depending on the site of compression, symptoms may vary in severity and location.

Risk factors

  • Age (common between 30-50 years).
  • Obesity (increases spinal load).
  • Occupational strain (e.g., heavy lifting, prolonged sitting).
  • History of lumbar disc disease.
  • Poor posture or lack of core strength.
  • Diabetes (increases risk of peripheral neuropathy).

Signs and symptoms

Sciatica is characterised by unilateral pain along the sciatic nerve pathway.

Common Features:

  • Radiating pain: starts in the lower back and extends down the buttock, posterior thigh, and leg.
  • Sharp, burning, or shooting pain: exacerbated by movement, coughing, or sneezing.
  • Numbness and tingling: often in the affected leg or foot.
  • Muscle weakness: difficulty with dorsiflexion or plantarflexion in severe cases.
  • Reduced reflexes: especially in the knee (L4) or ankle (S1).

Red Flag Symptoms (Suggesting Serious Pathology):

  • Bilateral symptoms or progressive weakness.
  • Bladder or bowel dysfunction: possible cauda equina syndrome.
  • Severe, worsening pain unresponsive to treatment.
  • Unexplained weight loss: consider malignancy.
  • History of malignancy or trauma.

Investigations

  • Clinical assessment: diagnosis is largely clinical.
  • Straight leg raise (SLR) test: positive if pain occurs between 30-70° of leg elevation.
  • Crossed SLR test: pain in the affected leg when raising the opposite leg suggests disc herniation.
  • MRI lumbar spine: indicated if symptoms persist >6 weeks or red flags are present.
  • X-ray lumbar spine: used if spinal stenosis or spondylolisthesis is suspected.
  • Nerve conduction studies (NCS): if differentiating from peripheral neuropathy.

Management

1. Conservative Treatment (First-Line):

  • Analgesia:
    • First-line: NSAIDs (e.g., ibuprofen, naproxen) with gastroprotection if needed.
    • Second-line: consider neuropathic agents (e.g., amitriptyline, gabapentin) if neuropathic pain is present.
    • Avoid opioids unless in severe, short-term cases.
  • Activity modification: encourage movement; prolonged bed rest is not recommended.
  • Physiotherapy: core strengthening and posture correction.
  • Heat therapy and massage: symptomatic relief.

2. Pharmacological Treatment (If Pain Persists):

  • Neuropathic pain relief: amitriptyline, duloxetine, pregabalin.
  • Oral corticosteroids: short courses may be considered in acute cases.

3. Interventional Treatment:

  • Epidural steroid injection: for persistent, severe cases.

4. Surgical Intervention (If Severe or Persistent Symptoms >6 Weeks):

  • Microdiscectomy: if significant disc herniation with nerve compression.
  • Lumbar decompression: for spinal stenosis-related sciatica.

5. Referral and Follow-Up:

  • Refer to physiotherapy if pain persists beyond 6 weeks.
  • Urgent referral for red flag symptoms (e.g., cauda equina suspicion).
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