Cervical Spondylotic Myelopathy

Cervical spondylotic myelopathy is a progressive disorder of the spinal cord caused by chronic compression from degenerative changes of the cervical spine: disc bulge, osteophytes, ligamentum flavum hypertrophy, facet arthropathy and ossification of the posterior longitudinal ligament. It is the commonest cause of spinal cord dysfunction in adults over 55 years.

Degenerative cervical changes are present in over 85% of people over 70 years, but only a minority develop myelopathy. It affects men more often than women, and the usual levels are C4 to C5, C5 to C6 and C6 to C7. A congenitally narrow canal (under 13 mm), a history of neck trauma, and ossification of the posterior longitudinal ligament (more common in East Asia, with diabetes) raise the risk.

The course is variable: some patients remain stable for years, but many have stepwise or slow decline, and mild disease progresses in 20 to 60% over several years. A minor hyperextension injury in a stenotic canal may cause a central cord syndrome. Complications are hand clumsiness, gait disorder, falls, bladder dysfunction, chronic neck pain, and permanent disability.

Pathophysiology.

Static compression (canal narrowing) and dynamic factors (instability, kyphosis, repetitive flexion and extension) deform and injure the cord. Chronic compression causes microvascular ischaemia, venous congestion, disruption of the blood spinal cord barrier, neuronal and oligodendrocyte apoptosis, demyelination, and Wallerian degeneration of the long tracts. Gliosis and cavitation produce the T2 signal change on MRI.

Insidious clumsiness of the hands (difficulty with buttons, handwriting, dropping objects), numbness in the hands, an unsteady and stiff gait, leg stiffness, falls, neck stiffness, and Lhermitte sign (electric shock on neck flexion). Bladder urgency and frequency appear late. Neck pain is variable, and may be absent.

Examination shows upper motor neurone signs in the legs (hyperreflexia, clonus, spasticity, Babinski sign), Hoffmann sign, inverted supinator reflex, finger escape sign, a slow grip and release test (under 20 cycles in 10 seconds), impaired tandem gait, reduced hand sensation and wasting of hand muscles. Lower motor neurone signs at the compressed level may coexist. Severity is graded with an 18-point myelopathy score (mild 15 to 17, moderate 12 to 14, severe 11 or under) and the Nurick grade.

• MRI of the cervical spine (the key test): cord compression, loss of cerebrospinal fluid around the cord, T2 hyperintensity (injury and gliosis), T1 hypointensity (worse prognosis), canal diameter, disc levels, and ligamentum flavum.
• Standing flexion and extension radiographs: alignment, kyphosis, instability and listhesis.
• CT (bone detail, ossification of the posterior longitudinal ligament, canal diameter) or CT myelography if MRI is contraindicated.
• Electromyography and nerve conduction studies and somatosensory evoked potentials when the diagnosis is uncertain, to exclude neuropathy and motor neurone disease.
• Blood tests to exclude mimics: vitamin B12 and folate, thyroid function, HIV and syphilis serology, copper, ESR and CRP, and HbA1c.

Differential diagnosis.

• Motor neurone disease and multiple sclerosis.
• Subacute combined degeneration (vitamin B12 deficiency) and copper deficiency myelopathy.
• Syringomyelia, spinal tumour and cord infarction.
• Carpal tunnel and cubital tunnel syndromes, peripheral neuropathy, normal pressure hydrocephalus and parasagittal meningioma.

Surgery is the only treatment that decompresses the cord and halts progression. No drug treats the underlying compression.

Mild disease (myelopathy score 15 to 17). Either structured non-operative care (neck strengthening exercises, avoidance of high risk activity and neck extension, a short period in a soft collar only for comfort, review every 3 to 6 months with MRI if symptoms change) or early surgery. The choice is based on the patient's wishes and progression. Surgery is offered promptly if there is any decline.

Moderate and severe disease. Decompressive surgery is advised without delay. Results are better when the symptom duration is under 1 to 2 years and the MRI shows no T1 change.

Surgical options.

• Anterior approach: anterior cervical discectomy and fusion for 1 to 2 levels, corpectomy for retrovertebral compression, or a hybrid construct; suited to kyphosis or focal disease.
• Posterior approach: laminoplasty (preserves motion, for multilevel disease with preserved lordosis), or laminectomy with instrumented fusion (multilevel disease with kyphosis or instability).
• Combined approaches for severe, multilevel kyphotic disease.
• Outcomes: about 50 to 70% improve in function; surgery aims to stop deterioration.
• Complications: C5 root palsy 5 to 12% (posterior), dysphagia (up to 30% early, 5% persistent after anterior surgery), recurrent laryngeal nerve palsy 1 to 3%, dural tear, epidural haematoma with airway compromise. Other complications are infection 1 to 2%, pseudarthrosis, axial neck pain (after laminoplasty), and adjacent segment disease (about 3% a year).
• Intraoperative neurophysiological monitoring; maintain mean arterial pressure at least 80 to 85 mm Hg during surgery; careful neutral neck positioning, with awake fibre optic intubation when stenosis is severe.

Symptomatic drug treatment.

• Spasticity: baclofen 5 mg orally three times daily, increased every 3 days to 20 mg three times daily (maximum 100 mg daily; reduce with renal impairment; avoid abrupt withdrawal because of seizures and rebound spasticity).
• Alternatively, tizanidine 2 mg orally at night, increased to 4 mg three times daily (maximum 36 mg daily; monitor liver function; avoid with ciprofloxacin and fluvoxamine).
• Neuropathic pain: gabapentin 300 mg orally at night, increased by 300 mg every 1 to 3 days to 300 to 600 mg three times daily (maximum 3600 mg daily; reduce at creatinine clearance under 60 mL/min).
• Alternatively, pregabalin 75 mg orally at night or twice daily, increased to 150 mg twice daily (maximum 300 mg twice daily).
• Bladder urgency: mirabegron 25 mg orally once daily, increased to 50 mg after 4 to 8 weeks (monitor blood pressure; avoid with severe uncontrolled hypertension). Anticholinergics such as oxybutynin 2.5 to 5 mg orally two to three times daily are avoided in older patients with cognitive impairment.
• Riluzole and corticosteroids have not been shown to improve outcomes and are not used routinely.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL). With severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Perioperative adjuncts. Dexamethasone 8 mg intravenously once at induction may reduce nausea, airway swelling and early dysphagia (monitor glucose in diabetes). Tranexamic acid 15 mg/kg (maximum 1 g) intravenously over 10 minutes before incision (avoid with a history of thromboembolism, active intravascular clotting, seizures, or recent coronary stent). Enoxaparin 40 mg subcutaneously once daily started 24 to 48 hours after surgery once haemostasis is secure and continued for 7 to 14 days (20 mg once daily at creatinine clearance under 30 mL/min).

Analgesia after surgery. Paracetamol 1 g orally every 6 hours (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment). Oral morphine 5 to 10 mg every 4 hours as needed for up to 3 to 5 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2). Laxative; lozenges and soft diet for dysphagia.

Monitoring. Neurological examination every 4 to 6 hours in the first 24 to 48 hours (neck swelling or breathing difficulty is an emergency), then review at 2 weeks, 6 weeks, 3 months, 6 months and 12 months with radiographs. Myelopathy score at each visit. Mild non-operative cases: review every 3 to 6 months, and MRI if there is any new sign.

Referral and escalation. Refer every suspected cervical myelopathy urgently (within 2 weeks) to a spinal surgeon. Emergency referral for rapid deterioration, new bladder or bowel loss, central cord syndrome after trauma, or airway compromise after surgery.

Special groups.

• Ossification of the posterior longitudinal ligament: laminoplasty or fusion; higher risk of cerebrospinal fluid leak and post-operative progression.
• Asymptomatic cord compression on MRI: no surgery; counsel about warning symptoms and the risk of injury with trauma.
• Rheumatoid arthritis, Down syndrome and other causes of atlantoaxial instability: assess the craniocervical junction.
• Anticoagulated patients: plan interruption with the prescribing team; kidney impairment: reduce baclofen, gabapentin, pregabalin, morphine and enoxaparin doses.