Low back pain

Low back pain is pain between the twelfth rib and the gluteal folds, with or without leg pain. Most cases are nonspecific and mechanical.

Epidemiology. It is among the leading causes of disability worldwide. Lifetime prevalence is 60% to 80%. Most acute episodes improve within 6 weeks, recurrence is common, and a minority become chronic. Serious spinal pathology causes a small minority of presentations, most often vertebral fracture, then malignancy, infection and cauda equina syndrome.

Classification by duration. Acute under 6 weeks, subacute 6 to 12 weeks, chronic over 12 weeks.

Classification by pattern.

• Nonspecific mechanical pain.
• Radicular pain (nerve root), extending past the knee.
• Neurogenic claudication (stenosis).
• Inflammatory back pain.
• Pain from serious spinal pathology.
• Referred pain from the viscera, aorta, kidneys or pelvis.

Mechanisms. Pain arises from discs, facet joints, sacroiliac joints, muscle and ligament, and nerve roots. Central sensitisation sustains chronic pain. Psychosocial yellow flags predict chronicity: fear avoidance, catastrophising, depression, job dissatisfaction and compensation claims. Degenerative changes on imaging are common in people without pain and correlate poorly with symptoms.

History.

• Onset and mechanism (lifting, trauma), age, site, radiation, character.
• Mechanical pattern: worse with movement, eased by lying.
• Inflammatory pattern: onset under 40 years, insidious, over 3 months, morning stiffness over 30 minutes, eased by exercise and not rest, night pain in the second half of the night, alternating buttock pain.
• Neurogenic claudication: leg symptoms on walking or standing, relieved by sitting or flexion.
• Night or rest pain, fever, weight loss, previous cancer, intravenous drug use, immunosuppression, tuberculosis contact, recent infection or spinal procedure.
• Long term corticosteroids, osteoporosis risk, trauma.
• Bladder or bowel dysfunction, saddle numbness, sexual dysfunction, bilateral sciatica, progressive weakness.
• Abdominal pain, tearing pain, syncope (aorta); urinary symptoms or haematuria (kidney); gynaecological symptoms.
• Psychosocial and work factors.

Examination.

• Temperature, pallor, posture, spinal and percussion tenderness (infection or fracture), range of movement, Schober test (under 5 cm increase suggests ankylosing disease).
• Lower limb power, knee and ankle reflexes, dermatomal sensation (L4, L5, S1), gait on heels and toes.
• Straight leg raise (sensitive for disc herniation, about 90%, but not specific) and crossed straight leg raise (specific, about 90%). Femoral stretch test.
• Saddle sensation and anal tone when cauda equina syndrome is suspected.
• Sacroiliac provocation tests, hip examination.
• Abdomen including aorta, peripheral pulses, renal angle, prostate and breasts where relevant.

Red flags.

• New bladder or bowel dysfunction, saddle anaesthesia, bilateral radiculopathy, progressive motor weakness.
• Onset under 20 or over 50 years.
• Known cancer, unexplained weight loss.
• Fever, intravenous drug use, immunosuppression.
• Significant trauma, osteoporosis, prolonged corticosteroids.
• Constant progressive pain, worse at night or lying, thoracic pain.
• Pulsatile abdominal mass or syncope.

Serious causes.

• Cauda equina syndrome and metastatic spinal cord compression.
• Primary and metastatic spinal tumours (breast, prostate, lung, kidney, thyroid), myeloma.
• Vertebral osteomyelitis, discitis and spinal epidural abscess; spinal tuberculosis (Pott disease).
• Vertebral fracture: osteoporotic, traumatic, pathological.
• Abdominal aortic aneurysm and dissection.

Common causes.

• Nonspecific mechanical pain, muscle and ligament strain.
• Lumbar disc herniation with radiculopathy.
• Lumbar spinal stenosis, facet joint arthropathy, spondylolisthesis, spondylolysis.
• Sacroiliac joint dysfunction, piriformis syndrome.

Inflammatory and metabolic. Axial spondyloarthritis (including ankylosing spondylitis), osteoporosis, osteomalacia, Paget disease, hyperparathyroidism.

Referred and non spinal. Pyelonephritis, renal colic, pancreatitis, retrocaecal appendicitis, endometriosis, pelvic inflammatory disease, prostatitis, hip disease, pregnancy related pelvic girdle pain.

Functional and psychosocial. Fibromyalgia pattern, chronic widespread pain, depression.

1. No imaging or blood tests for nonspecific pain without red flags. Imaging does not improve outcomes and finds incidental change.
2. Suspected cauda equina syndrome or cord compression: emergency MRI of the whole spine, immediately.
3. Suspected cancer or infection: full blood count, ESR, CRP, calcium, alkaline phosphatase, creatinine, serum protein electrophoresis or free light chains, urinalysis, blood cultures if febrile, HIV test, glucose, and PSA in men when prostate cancer is suspected. Then MRI of the spine with gadolinium. MRI is the preferred imaging; use CT if MRI is contraindicated.
4. Spinal tuberculosis: MRI, tuberculosis testing, image guided or open biopsy for culture and histology.
5. Suspected fracture: plain radiographs or CT; bone density scanning and a metabolic screen for osteoporosis.
6. Persistent radicular pain beyond 6 weeks, or a progressive deficit: MRI when intervention is being considered.
7. Suspected axial spondyloarthritis: CRP, HLA-B27, MRI of the sacroiliac joints (bone marrow oedema on fat suppressed sequences). Classification needs sacroiliitis on imaging plus one spondyloarthritis feature, or HLA-B27 plus two features.
8. Suspected aortic aneurysm: bedside ultrasound then urgent CT angiography.
9. Pregnancy test before imaging with radiation.

Limits. Plain radiographs have low yield. ESR and CRP are nonspecific. MRI findings must be matched to the clinical picture.

Nonspecific pain.

• Reassure, advise staying active, avoid bed rest, return early to work, local heat.
• Ibuprofen 400 mg orally three times daily with food (maximum 2.4 g daily) for 7 to 14 days, or naproxen 500 mg orally twice daily (maximum 1 g daily), with gastric protection when at risk. Avoid in peptic ulcer, heart failure, anticoagulation, late pregnancy and with eGFR under 30 mL/min.
• Paracetamol 1 g orally every 6 hours (maximum 4 g daily; 3 g in frail patients or under 50 kg) has little benefit alone and may be added.
• Benzodiazepines are not advised. Opioids are not first line. If a short course is needed for severe pain, tramadol 50 mg orally every 6 hours (maximum 400 mg daily) for 3 to 5 days; with eGFR under 30 mL/min lengthen the interval to 12 hours (maximum 200 mg daily).
• Subacute and chronic: supervised exercise, physiotherapy, spinal manipulation, cognitive behavioural therapy, structured self management, weight loss and smoking cessation. Duloxetine 30 mg orally daily, increased to 60 mg, has modest benefit. Avoid injections and traction.

Radicular pain. NSAID and exercise first. For neuropathic pain, pregabalin 75 mg orally twice daily (maximum 300 mg twice daily, reduced in renal impairment) or amitriptyline 10 mg at night, increased to 50 mg. Consider epidural steroid injection for severe pain beyond 6 weeks. Discectomy for refractory radiculopathy at 6 to 12 weeks, or sooner with a progressive deficit.

Serious causes.

• Cauda equina syndrome: admit, immediate MRI, neurosurgical decompression within 24 to 48 hours.
• Metastatic cord compression: dexamethasone 16 mg orally or intravenously once daily with gastric protection, urgent oncology and radiotherapy or surgical decompression.
• Vertebral infection: blood cultures before antibiotics in the stable patient and delay antibiotics until a microbiological diagnosis. With sepsis or neurological deficit start immediately: flucloxacillin or cloxacillin 2 g intravenously every 6 hours plus ceftriaxone 2 g intravenously daily, adding vancomycin 15 to 20 mg/kg intravenously every 8 to 12 hours when MRSA is likely. Usual duration is 6 weeks.
• Spinal tuberculosis: four drug antituberculous therapy for 2 months then rifampicin and isoniazid, usually 9 to 12 months in total, with specialist direction.
• Osteoporotic fracture: analgesia, early mobilisation, calcium, vitamin D, alendronic acid 70 mg orally once weekly (or zoledronic acid 5 mg intravenously once yearly).
• Axial spondyloarthritis: continuous full dose NSAID (for example naproxen 500 mg twice daily) with exercise; rheumatology for biologic therapy after failure of two NSAIDs.
• Aortic aneurysm and dissection, renal and pelvic causes: emergency or targeted management of the cause.

Monitoring. Review at 2 weeks and 6 weeks. Reassess red flags and neurological status.

Referral and escalation. Immediate: cauda equina syndrome, cord compression, aortic pathology. Urgent: suspected tumour, infection, fracture with instability. Routine: persistent radiculopathy, stenosis, chronic pain needing a multidisciplinary programme.

Admission. Cauda equina syndrome, cord compression, vertebral infection with sepsis or deficit, unstable fracture, pain needing parenteral analgesia, suspected aortic pathology.

Safety netting. Return the same day for urinary retention or incontinence, saddle numbness, bilateral leg weakness or numbness, fever, or progressive weakness.

Special groups. Pregnancy: paracetamol first line, avoid NSAIDs in the third trimester, consider pelvic girdle pain, pyelonephritis and pre-eclampsia. Children: back pain is rarely nonspecific; investigate for tumour, discitis, spondylolysis and scoliosis. Older adults: osteoporotic fracture and stenosis, and renal adjustment of drugs. HIV and endemic regions: keep spinal tuberculosis on the list.