Posterior Cord Syndrome

Posterior cord syndrome is a rare spinal cord syndrome caused by lesions of the dorsal columns, with loss of vibration and joint position sense, sensory ataxia and preservation of motor function and pain and temperature sensation. It is caused by compression, metabolic, infectious and inflammatory disease, and by posterior spinal artery infarction.

It makes up under 1% of spinal cord injuries, and the true frequency in non-traumatic myelopathy is unknown. It is usually seen in adults with dorsal column disease from B12 deficiency or tabes dorsalis.

Causes. Vitamin B12 deficiency, copper deficiency, neurosyphilis (tabes dorsalis), multiple sclerosis, tumours of the posterior cord or dorsal compression, hyperextension injury, posterior spinal artery infarction, HIV myelopathy, nitrous oxide misuse and Friedreich ataxia.

Course. Depends on cause; treatable causes such as B12 deficiency and syphilis improve with treatment, while structural disease needs decompression.

Pathophysiology.

Damage to the dorsal columns (fasciculus gracilis and cuneatus) interrupts proprioception and fine touch, which are supplied by the paired posterior spinal arteries.

Loss of proprioceptive input causes sensory ataxia and pseudoathetosis.

• Loss of vibration and joint position sense, with stamping, wide based gait that worsens in the dark.
• Positive Romberg test; loss of two point discrimination and stereognosis.
• Lhermitte sign and band like paraesthesia.
• Lightning pains, Argyll Robertson pupils, absent ankle reflexes and Charcot joints in tabes dorsalis.
• Motor strength, pain and temperature sense are usually preserved.

Red flags.

• Progressive weakness, sphincter loss or a sensory level (compression).
• Weight loss, night sweats or cancer history.
• Neurosyphilis in a person with HIV or unprotected sex.

• Detailed examination of sensory modalities, gait and reflexes.
• MRI of the spine and brain with contrast: dorsal column T2 hyperintensity, compression, tumour or demyelination.
• Blood tests: B12, methylmalonic acid, copper, folate, HIV, syphilis serology (treponemal and non-treponemal), glucose, thyroid function and vitamin E.
• Lumbar puncture: cells, protein, VDRL, oligoclonal bands, and polymerase chain reaction tests if indicated.
• Somatosensory evoked potentials and nerve conduction studies to separate central from peripheral loss.

Differential diagnosis. Subacute combined degeneration, sensory neuronopathy, tabes dorsalis, multiple sclerosis, Friedreich ataxia, large fibre neuropathy, compressive cervical myelopathy, copper deficiency myelopathy and functional sensory loss.

• Treat the cause.
• B12 deficiency: hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement, then 1 mg every 2 months for life when the cause persists. Maximum 1 mg for each injection. Monitor potassium early in severe anaemia, full blood count and neurological recovery. Avoid in hypersensitivity to cobalamin; use caution in Leber disease. Do not give folic acid alone.
• Neurosyphilis: benzylpenicillin 18 to 24 million units daily intravenously, given as 3 to 4 million units every 4 hours (or by continuous infusion), for 14 days. Maximum 24 million units daily. Monitor renal function, electrolytes (sodium load) and Jarisch-Herxheimer reaction (give prednisolone 20 to 40 mg orally daily for 3 days as cover if risk is high). Avoid in penicillin allergy and use ceftriaxone 2 g intravenously once daily for 14 days (maximum 2 g daily; reduce in severe hepatic and renal impairment together). Retest serology and cerebrospinal fluid at 6 and 12 months.
• Copper deficiency: treat the cause (stop zinc excess, correct malabsorption) with oral copper replacement through a specialist.
• Compression or tumour: urgent spinal surgery or radiotherapy.
• Multiple sclerosis: methylprednisolone 1000 mg intravenously once daily for 3 to 5 days for relapse. Maximum 5 g in a course. Monitor blood pressure, glucose, mood and infection.
• Rehabilitation: balance and gait training with visual and tactile cues, walking aids, home safety and falls prevention.
• Neuropathic pain: pregabalin 75 mg orally twice daily, increased after 1 week to 150 mg twice daily, then to a maximum of 300 mg twice daily (600 mg daily). Monitor sedation, weight gain, oedema and misuse. Adjust for renal function: creatinine clearance 30 to 59 mL/min, 75 to 300 mg daily; 15 to 29 mL/min, 25 to 150 mg daily; under 15 mL/min, 25 to 75 mg daily.

Monitoring. Review at 4 to 6 weeks and 3 months, then every 6 months; track gait, proprioception and the cause (B12, serology).

Referral and escalation. Neurology for diagnosis; neurosurgery for compression; infectious diseases or genitourinary medicine for syphilis; haematology for B12 deficiency.

Special groups. Pregnancy with syphilis: urgent treatment with penicillin to prevent congenital syphilis. People with HIV: treat both infections.