Sciatica

Sciatica is pain radiating down the leg along the distribution of the sciatic nerve or its constituent L4 to S3 nerve roots, usually below the knee, caused by compression or inflammation of a nerve root, most often from a lumbar disc herniation.

• Lifetime prevalence 10 to 40 percent; peak onset between 30 and 50 years; about 90 percent of cases are due to disc herniation at L4/5 or L5/S1.
• Other causes: lateral recess or foraminal stenosis, spondylolisthesis, piriformis syndrome (deep gluteal syndrome), epidural abscess, tumour or metastasis, vertebral fracture, spinal tuberculosis, diabetic radiculopathy, herpes zoster, and pelvic mass or pregnancy.
• Natural history is favourable: about 60 to 80 percent improve substantially within 6 to 12 weeks, with approximately 20 to 30 percent having persistent symptoms at 1 year.
• Risk factors: smoking, obesity, heavy lifting, vibration (driving), prolonged sitting, pregnancy and previous episodes.

• Unilateral leg pain, burning or shooting, worse than back pain, extending below the knee into the foot, often with paraesthesia, numbness and sometimes weakness.
• Pain worse on sitting, coughing, sneezing or straining; relieved by walking or lying with the knees flexed.
• Dermatomal pattern: L4 (anteromedial leg), L5 (lateral leg and dorsum of foot, great toe), S1 (lateral foot and sole, little toe).
• Signs: straight leg raise at 30 to 70 degrees reproducing leg pain (sensitivity about 90 percent), crossed straight leg raise (specific, about 90 percent), slump test, reduced ankle reflex (S1) or knee reflex (L4), weakness of great toe extension (L5) or plantar flexion (S1), foot drop.
• Cauda equina syndrome (surgical emergency): saddle anaesthesia, urinary retention or overflow incontinence, faecal incontinence, loss of anal tone, bilateral leg pain or weakness, sexual dysfunction.
• Other red flags: progressive motor deficit, fever or immunosuppression, injection drug use, cancer history, unexplained weight loss, major trauma, osteoporosis or long term steroid use, age under 20 or over 55 with new pain, night or rest pain.

• Clinical in the first 6 weeks; do not image routinely.
• MRI lumbar spine within 24 hours for suspected cauda equina syndrome (emergency, same day admission); promptly for progressive neurological deficit, suspected infection or malignancy.
• MRI when severe symptoms persist at 6 to 12 weeks and when injection or surgery is considered, to confirm a concordant lesion. Many asymptomatic adults have disc bulges, so correlate with examination.
• Blood tests when infection or malignancy suspected: FBC, ESR, CRP, calcium, alkaline phosphatase, PSA in men, HbA1c.
• Nerve conduction studies and EMG at 3 weeks or longer if the cause is unclear (peripheral neuropathy versus radiculopathy).
• Differentials: hip osteoarthritis, sacroiliac joint pain, piriformis syndrome, peripheral neuropathy, peripheral arterial disease (claudication), spinal stenosis, trochanteric bursitis, abdominal aortic aneurysm, pelvic tumour.

Emergency

• Suspected cauda equina syndrome: arrange immediate hospital transfer for emergency MRI and decompression surgery, ideally within 24 hours of onset of sphincter involvement.

Conservative (most patients)

• Reassure and explain the usually favourable course; advise staying active and continuing normal activities as pain allows; avoid bed rest beyond 1 to 2 days; return to work early with modified duties.
• Heat packs; physiotherapy with back and core exercises and neural mobilisation; weight loss; stop smoking.
• Analgesia:
  • Ibuprofen 400 mg orally three times daily with food, or naproxen 500 mg twice daily, for up to 2 to 3 weeks with omeprazole 20 mg daily; avoid in renal impairment, peptic ulcer, heart failure, uncontrolled hypertension and anticoagulation.
  • Paracetamol 1 g up to four times daily adds little benefit alone but may be combined.
  • Neuropathic agents have modest benefit: amitriptyline 10 mg at night increasing to 50 mg; or duloxetine 30 mg daily increasing to 60 mg; or gabapentin 300 mg at night increasing to 300 to 600 mg three times daily; or pregabalin 75 mg twice daily increasing to 150 mg twice daily (renal dose adjustment). Stop if no benefit after 4 weeks at an adequate dose.
  • Opioids: avoid; if unavoidable for severe pain, tramadol 50 mg every 6 hours as needed or codeine 30 mg with paracetamol for no more than 5 to 7 days.
  • Benzodiazepines and long term muscle relaxants: avoid; diazepam 2 mg three times daily for up to 5 days only for severe acute spasm.
  • Oral prednisolone gives little sustained benefit and is not routine.

Interventional

• Epidural or transforaminal steroid injection (for example triamcinolone 40 to 80 mg or methylprednisolone 40 to 80 mg with lidocaine, under imaging) for severe radicular pain persisting beyond 4 to 6 weeks; relief lasts weeks to months and may postpone or avoid surgery. Risks: infection, bleeding, dural puncture headache, transient hyperglycaemia; avoid on anticoagulants without suspension.

Surgery

• Microdiscectomy for: cauda equina syndrome; progressive or severe motor weakness; intractable pain after 6 to 12 weeks of conservative treatment with a concordant disc herniation on MRI. Outcome is better than conservative care at 1 year for leg pain, with similar long term outcomes.

Follow up and safety netting

• Review at 2 and 6 weeks. Give written advice to attend urgently if there is difficulty passing urine, loss of bladder or bowel control, numbness around the genitals or buttocks, weakness in both legs, or progressive leg weakness.

Special groups

• Pregnancy: use paracetamol, physiotherapy, support belts and heat; avoid NSAIDs from 20 weeks; avoid gabapentinoids unless essential; epidural steroid injection only with specialist input.
• Renal impairment: avoid NSAIDs; reduce gabapentin and pregabalin by creatinine clearance.