Syringomyelia

Syringomyelia is a fluid filled cavity within the spinal cord. Hydromyelia is dilatation of the central canal lined by ependyma, and the two often coexist. Extension into the brainstem is syringobulbia. Prevalence is about 8 per 100,000, and onset is usually between 25 and 40 years.

Causes

• Chiari I malformation: the commonest cause. A syrinx occurs in 20 to 70% of patients with tonsillar descent.
• Other craniocervical anomalies: Chiari II, basilar invagination, platybasia.
• Post traumatic: develops months to years after spinal cord injury in 3 to 5% of cases.
• Post inflammatory arachnoiditis: meningitis, tuberculosis, subarachnoid haemorrhage, surgery.
• Intramedullary tumours: ependymoma, astrocytoma, haemangioblastoma.
• Spinal dysraphism and tethered cord.
• Idiopathic.

Pathophysiology: obstruction of CSF flow at the foramen magnum or in the spinal subarachnoid space causes a systolic pulse pressure wave that drives CSF along perivascular spaces into the cord. The cavity expands and dissects through the cord, typically in the cervical and upper thoracic segments.

Neurological injury follows a predictable sequence

• Crossing spinothalamic fibres in the anterior white commissure are damaged first.
• Anterior horn cells follow.
• Lateral corticospinal and dorsal column tracts are affected later.

The course is slowly progressive, and spontaneous stabilisation can occur.

The classic presentation is a cape or suspended distribution of dissociated sensory loss over the neck, shoulders and arms:

• Loss of pain and temperature.
• Preserved light touch, vibration and proprioception.

Consequences

• Painless burns and injuries to the hands.
• Neuropathic arthropathy (Charcot joints), particularly of the shoulder and elbow.
• Neuropathic pain, which is often dysaesthetic and may be the first symptom.

Motor and autonomic features

• Lower motor neuron signs in the arms: hand wasting, claw hand, fasciculations, areflexia.
• Later, spastic paraparesis with hyperreflexia, Babinski signs and bladder dysfunction.
• Horner syndrome from ciliospinal involvement.
• Scoliosis in 25 to 85%, especially when onset is in childhood.
• Trophic skin changes, hyperhidrosis or anhidrosis.

Syringobulbia

• Tongue atrophy with fasciculations, palatal weakness, dysphagia, vocal cord paralysis.
• Downbeat or other nystagmus, vertigo, sleep apnoea.
• Facial numbness in an onion skin pattern from the spinal trigeminal nucleus.

Chiari related symptoms include occipital headache triggered by cough or Valsalva. Post traumatic syringomyelia presents with new pain, ascending sensory level, increasing spasticity, reduced reflexes or hyperhidrosis.

Differential diagnosis includes intramedullary tumour, multiple sclerosis, cervical spondylotic myelopathy, motor neuron disease, leprosy, hereditary sensory neuropathy and subacute combined degeneration.

MRI of the whole neuraxis (brain, craniocervical junction and entire spine) with and without gadolinium is the diagnostic investigation:

• A longitudinal cavity with CSF signal, smooth margins and cord expansion.
• Tonsillar descent of 5 mm or more below the foramen magnum in Chiari I.
• Contrast enhancement to exclude an underlying tumour, such as a haemangioblastoma with a mural nodule.
• Features of tethered cord, arachnoiditis or myelomalacia in post traumatic cases.

Further tests

• Phase contrast cine MRI of CSF flow at the foramen magnum to assess obstruction.
• CT myelography when MRI is contraindicated.
• Neurophysiology (EMG, somatosensory evoked potentials) for baseline function.
• Standing spine radiographs for scoliosis, which in syrinx related curves are often left thoracic, painful and rapidly progressive.
• Urodynamics for bladder dysfunction.

Serial MRI every 6 to 12 months monitors a syrinx that is small or asymptomatic, and clinical deterioration with stable imaging should prompt a search for another cause.

Management depends on the cause and on whether the patient is symptomatic or progressing.

Asymptomatic or minimally symptomatic syrinx

• Observation with annual clinical review and MRI.
• Avoid heavy lifting, straining and contact sports in Chiari malformation.

Chiari associated syringomyelia

• Posterior fossa decompression with suboccipital craniectomy, C1 laminectomy and duraplasty, with or without tonsillar reduction. The syrinx improves or resolves in about 70 to 90%.
• Persistent or progressive syrinx after decompression: syringosubarachnoid or syringopleural shunt, or revision of the decompression.

Post traumatic or arachnoiditis related syringomyelia

• Untethering, arachnolysis and duraplasty to restore CSF flow, or syrinx shunting. Recurrence is more frequent than in Chiari disease.

Tumour related syringomyelia

• Resection of the tumour, after which the cavity usually collapses.

Tethered cord: untethering.

Symptomatic and supportive therapy

• Neuropathic pain: gabapentin starting at 300 mg at night, titrated to 1200 mg three times daily as needed, pregabalin 150 to 600 mg daily in divided doses, duloxetine 60 mg daily, or amitriptyline 10 to 75 mg at night. Carbamazepine 200 to 400 mg twice daily is an option for lancinating pain.
• Spasticity: baclofen 5 mg three times daily increasing to a maximum of 80 mg/day, tizanidine 2 mg at night increasing to 36 mg/day in divided doses, and intrathecal baclofen for severe cases.
• Bladder dysfunction: clean intermittent catheterisation and oxybutynin 5 mg two to three times daily for detrusor overactivity.
• Joint protection, water temperature checks, skin and burn prevention, and occupational therapy.
• Scoliosis: bracing is generally ineffective. Decompress the syrinx first, then correct the deformity surgically if it progresses.

Surgery stabilises or improves symptoms in about 70 to 80%, and established motor and sensory loss rarely recovers fully. Recurrence after decompression occurs in about 10%.