Epidemiology

• Cauda equina syndrome is rare. It occurs mainly in adults but can occur at any age.
• A congenitally narrow spinal canal or acquired spinal stenosis arising from a combination of degenerative changes of the disc and the segmental posterior joints may predispose to cauda equina syndrome.^[2]

Causes

• Herniation of a lumbar disc; the commonest cause of cauda equina syndrome is compression arising from large central lumbar disc herniation at the L4/5 and L5/S1 level.^[2]
• Tumours: metastases, lymphomas, spinal tumours.
• Trauma.
• Infection, including epidural abscess.^[3]
• Congenital, eg congenital spinal stenosis, kyphoscoliosis and spina bifida.
• Spondylolisthesis.
• Late-stage ankylosing spondylitis.
• Post-operative haematoma.
• Following spinal manipulation.^[4]
• Inferior vena cava thrombosis.
• Sarcoidosis.

Presentation

See also the separate article Examination of the Spine.

Clinical diagnosis of cauda equina syndrome is not easy.^[2] Most cases are of sudden onset and progress rapidly within hours or days. However cauda equina syndrome can evolve slowly and patients do not always complain of pain.

• Low back pain, with pain in the legs and unilateral or bilateral lower limb motor and/or sensory abnormality.
• Lower limb motor weakness and sensory deficits: usually asymmetrical weakness with loss of reflexes dependent on the affected nerve root (increased lower limb reflexes and other upper motor neurone signs such as extensor plantar responses may indicate spinal cord involvement and exclude the diagnosis of cauda equina syndrome).
• Bowel and/or bladder dysfunction with saddle and perineal anaesthesia.
• Urinary dysfunction may include retention, difficulty starting or stopping a stream of urine, overflow incontinence and decreased bladder and urethral sensation.
• Bowel disturbances may include faecal incontinence, constipation. Rectal examination may reveal loss of anal tone and sensation.
• Sexual dysfunction.

Investigations

• The diagnosis is usually possible from the history and examination.
• Further investigations are focused on localising the site of compression and the underlying cause.
• MRI scan is the preferred investigation to confirm the diagnosis and determine the level of the compression and any underlying cause.^[2]
• Myelography and CT are also sometimes used.
• Urodynamic studies: may be required to monitor recovery of bladder function following decompression surgery.

Differential diagnosis

• Conus medullaris syndrome (the conus medullaris is located above the cauda equina at T12-L1; nerve root pain is less prominent and the main features are urinary retention and constipation.^[5])
• Mechanical back pain or prolapsed lumbar disc.
• Fracture of lumbar vertebrae due to trauma.
• Spinal tumour.
• Spinal cord compression.
• Peripheral neuropathy.

Management

Patients should be referred immediately for a neurosurgical consultation. Urgent surgical spinal decompression is indicated for most patients to prevent permanent neurological damage.

• Immobilise spine if cauda equina syndrome is due to trauma.
• Surgery is indicated to remove blood, bone fragments, tumour, herniated disc or abnormal bone growth.
• For patients with a herniated disk as the cause of cauda equina syndrome, early surgical decompression is recommended.^[6]
• Lesion debulking is required for space occupying lesions, eg tumours, abscess.
• If surgery cannot be performed, radiotherapy may relieve cord compression caused by malignant disease.
• Other treatment options may be useful in certain patients, depending on the underlying cause of the cauda equina syndrome:
  • Anti-inflammatory agents, including steroids, can be effective in patients with inflammatory causes, eg ankylosing spondylitis.
  • Infection causes should be treated with appropriate antibiotic therapy.
  • Patients with spinal neoplasms should be evaluated for chemotherapy and radiation therapy.
• Postoperative care includes addressing lifestyle issues, eg obesity, and also physiotherapy and occupational therapy, depending on residual lower limb dysfunction.

Complications

Complications are increasingly likely if diagnosis and appropriate management is delayed, and include residual:

• Paralysis
• Sensory abnormalities
• Bladder, bowel, and sexual dysfunction

Prognosis

• Prognosis is dependent on the aetiology and the time taken before effective treatment is provided.
• A degree of bladder and bowel function may be permanently lost.
• Late diagnosis and treatment increases the risk of a permanent neurological deficit.
• Patients with bilateral sciatica or complete perianal anaesthesia have a less favourable prognosis than patients with unilateral pain.