Clinical neuroanatomy and spinal cord syndromes

• A lesion anywhere along the nervous system announces itself through where it sits: cortex and internal capsule give focal deficits with specific patterns; the brainstem gives crossed signs; the spinal cord gives a level with tract signs below it; roots and nerves give segmental or named distributions; the neuromuscular junction and muscle give fatigable or proximal weakness.
• The quick bedside rule is to decide whether weakness is upper or lower motor neuron in type, because that separates cortex, brainstem, cord and root from nerve, junction and muscle.
• The spinal cord carries the corticospinal tract for voluntary movement, the spinothalamic tract for pain and temperature, and the dorsal columns for vibration and proprioception; knowing which tract is damaged names the syndrome.
• Classic cord patterns are central cord (arms worse than legs), anterior cord (motor and pain/temperature lost, proprioception spared), Brown-Sequard (same-side motor and proprioception loss, opposite-side pain/temperature loss), and syringomyelia (dissociated sensory loss in a cape distribution).
• Management depends on cause: urgent referral for compression or cauda equina, antispasticity therapy for stiffness, penicillin for tabes, and riluzole plus multidisciplinary care for ALS.

By the end of this page you should be able to:

1. Localise a neurological lesion to cortex, brainstem, spinal cord, root, nerve, neuromuscular junction or muscle from the clinical picture.
2. State the course and function of the main spinal cord tracts and predict the deficits from a lesion of each.
3. Recognise central cord, anterior cord, Brown-Sequard, syringomyelia, tabes dorsalis and ALS clinically.
4. Explain the difference between upper and lower motor neuron signs.
5. Plan the investigation of a suspected spinal cord syndrome, including the cut-offs used for referral.
6. Outline the guideline-based treatment of tabes, ALS and spasticity, with the doses that the guidelines specify.

A neurological lesion is damage at one point in the pathway that runs from the cerebral cortex through the brainstem and spinal cord, then along the nerve root, peripheral nerve, neuromuscular junction and muscle. Localisation is the skill of working backwards from the patient's deficits to the level of that damage. The first fork in the reasoning is whether weakness is upper or lower motor neuron in type, because that divides the nervous system in half.

Upper motor neuron (UMN) signs come from damage to the cell bodies or axons that descend from cortex to cord, most often in the internal capsule, brainstem, or spinal cord. Lower motor neuron (LMN) signs come from damage to the anterior horn cell, root, nerve, neuromuscular junction or muscle. Mixed UMN and LMN signs in the same regions are the hallmark of motor neuron disease.

Spinal cord syndromes are grouped by the territory damaged: central cord, anterior (ventral) cord, hemisection (Brown-Sequard), posterior column disease (tabes and subacute combined degeneration), and intrinsic cord cavitation (syringomyelia). Amyotrophic lateral sclerosis is a degenerative motor neuron disease that produces mixed UMN and LMN weakness without sensory loss.

Spinal cord syndromes are uncommon but high-stakes. Central cord syndrome is the most frequent partial spinal cord injury, accounting for 15 to 25% of spinal cord injuries, with about 11,000 new cases in the USA each year. Syringomyelia is responsible for up to 5% of cases of paraplegia. Anterior spinal artery syndrome is rare, with an incidence of about 3.1 per 100,000 per year in the USA, and it is the most common spinal cord stroke. Brown-Sequard syndrome makes up only 1 to 4% of traumatic spinal cord injuries. ^{[9][10][11][12]}

Tabes dorsalis is now rare, thanks to antibiotics. Between 1.5% and 9% of people with syphilis develop tabes dorsalis, and roughly 25 to 35% of syphilis cases develop neurosyphilis overall. It typically appears about 20 years after the original infection. Syphilis itself has risen recently, with primary and secondary cases increasing by 28.6% from 2020 to 2021. ^[7]

ALS affects 1 to 2.6 per 100,000 people (4 to 5 per 100,000 at any time). About 90 to 95% of cases are sporadic. Men's lifetime risk is 1 in 350 and women's 1 in 400, with onset around 64 years and peak risk near 75 years. Median survival is 3 to 5 years. ^[6]

Risk factors include neck hyperextension injury (central cord), aortic surgery and vascular disease (anterior cord), trauma or tumour (Brown-Sequard), HIV coinfection (neurosyphilis), and family history and age (ALS). Cauda equina syndrome requires emergency action and classically follows lumbar disc herniation.

The corticospinal (pyramidal) tract carries voluntary movement commands from cortex to cord. Its fibres descend through the internal capsule, decussate in the medulla, and run in the lateral cord. Damage anywhere above the anterior horn produces upper motor neuron signs: weakness with spasticity, hyperreflexia, clonus and an extensor plantar response.

The spinothalamic tract carries pain and temperature. Its fibres cross soon after entry and run in the anterolateral cord. The dorsal columns carry vibration and proprioception on the same side all the way to the medulla. Each lesion pattern follows from which of these tracts is damaged.

• Cortex or internal capsule: contralateral face, arm and leg weakness, often with aphasia or neglect; this is the typical stroke picture.
• Brainstem: crossed signs, meaning a cranial nerve palsy on one side with body weakness on the other; the level (midbrain, pons, medulla) determines which cranial nerve is affected.
• Spinal cord: a sensory level with tract signs below; paraparesis or tetraparesis, and often early bladder disturbance.
• Root: a dermatome and myotome pattern, depressed reflexes, radicular pain.
• Peripheral nerve: a named nerve territory, distal weakness, sensory loss in that nerve's distribution.
• Neuromuscular junction: fatigable weakness, ptosis, diplopia; eye and bulbar muscles prominent; reflexes and sensation preserved.
• Muscle: proximal, symmetric weakness, wasted muscles, no sensory loss.

Central cord syndrome damages the centre of the cord, where the cervical fibres for the hands are densely packed, so the arms and hands are weaker than the legs. ^[11] Anterior cord syndrome damages the anterior two-thirds of the cord, including the corticospinal and spinothalamic tracts, but spares the dorsal columns. ^[10] Brown-Sequard damages one half of the cord, so motor and dorsal-column function are lost on the same side and pain and temperature on the opposite side. ^[9] Syringomyelia is a fluid-filled cavity (syrinx) in the central canal; it first damages the anterior white commissure where spinothalamic fibres cross, producing dissociated sensory loss (pain and temperature lost, light touch preserved) in a cape distribution over the shoulders. ^[12] Tabes dorsalis damages the dorsal columns and dorsal roots, giving sensory ataxia, lightning pains and absent ankle reflexes. ^[7]

Upper versus lower motor neuron signs at the bedside:

Key cord-syndrome patterns:

Examination should include: cranial nerves and higher function (cortex), eye movements and facial sensation (brainstem), a sensory level and plantar responses (cord), dermatomes (root), named peripheral nerve territories (nerve), fatigable ptosis (junction), and proximal power and muscle bulk (muscle). Bladder and sexual function, and a rectal examination, complete the spinal assessment.

Red flags that need same-day action: severe back pain with new bladder, bowel or sexual dysfunction or perineal numbness (cauda equina), rapidly progressive symmetric weakness, respiratory weakness at rest, and signs of spinal cord compression. ^[3]

The approach follows the level and cause of the lesion.

• Compression or cauda equina: urgent specialist review and imaging; decompression when pressure or canal narrowing is present. ^[3]
• Syringomyelia: avoid Valsalva manoeuvres; surgical decompression at the foramen magnum or shunting when symptomatic or progressive. ^[12]
• Tabes dorsalis: intravenous aqueous crystalline penicillin G 18 to 24 million units per day (3 to 4 million units IV every 4 hours, or a continuous infusion) for 10 to 14 days; benzathine penicillin 2.4 million units IM weekly for 1 to 3 weeks may follow to complete duration. Ceftriaxone 1 to 2 g daily for 10 to 14 days, or procaine penicillin 2.4 million units IM daily plus probenecid 500 mg orally four times daily for 10 to 14 days, are alternatives. HIV testing is recommended at diagnosis. ^[5][7][8]
• Spasticity (from any UMN lesion): baclofen, tizanidine, or gabapentin; botulinum toxin for focal spasticity. ^[2]
• ALS: riluzole 50 mg twice daily, offered lifelong at diagnosis; tofersen for SOD1-mutant disease; multidisciplinary care with MND team reviews every 2 to 3 months; non-invasive ventilation for respiratory insufficiency; PEG for nutritional support; quinine 100 to 200 mg daily for muscle cramps. Edaravone is not recommended outside trials in the European guideline. ^[1][2][4]
• Cauda equina and myelopathy red flags: urgent referral in line with the NICE recognition and referral guideline. ^[3]

• Spinal cord injury brings respiratory failure, autonomic dysreflexia, pressure ulcers, deep venous thrombosis and pulmonary embolism. ^[11]
• ALS leads to respiratory decline, bulbar dysfunction, malnutrition, aspiration pneumonia and, in most cases, death within 3 to 5 years. ^[6]
• Untreated tabes or neurosyphilis can progress to paralysis, dementia, blindness and Charcot joints. ^[7]

Prognosis varies by syndrome. Brown-Sequard syndrome has the best recovery among the partial cord syndromes, with more than half recovering well and many walking again. Central cord syndrome generally recovers to at least 90% of motor function by 3 years. Anterior cord syndrome carries a less favourable outlook, with 9 to 23% mortality in spinal cord infarction and limited motor recovery in many. Syringomyelia is unpredictable and worsens in 10 to 50% of cases after decompression. ALS gives a median survival of 3 to 5 years. ^{[9][10][11][12][6]}

• Trauma prevention: falls reduction in older adults, road safety and spinal precautions at scene. ^[11]
• Screen for syphilis in at-risk and pregnant people; test for HIV at diagnosis of neurosyphilis. ^[5][8]
• Early recognition of red flags for cauda equina and spinal cord compression prevents permanent disability. ^[3]

• Pregnancy: neurosyphilis and tabes are treated with penicillin; penicillin-allergic pregnant patients should be desensitised. ^[5]
• Children: spinal cord injury is rarer; rhabdomyoma rather than cord pathology dominates paediatric masses, and syringomyelia presents with scoliosis. ^[12]
• Older adults: central cord syndrome is especially common after neck hyperextension in people with cervical spondylosis; ALS onset rises with age. ^[11][6]

• A careful neurological examination localises most lesions without imaging; the sensory level, reflexes and UMN features are the key tools.
• When MRI is unavailable, myelography or CT of the spine can assess compression; urgent referral pathways matter more than advanced imaging.
• Tabes and ALS care can be delivered with basic antibiotics, physiotherapy, simple assistive devices and family support where advanced interventions are unavailable.

• Localisation is the single most useful neurological skill, and it begins with UMN versus LMN signs.
• Spinal cord syndromes are predicted by knowing three tracts: corticospinal (motor), spinothalamic (pain and temperature) and dorsal columns (vibration and proprioception).
• Central cord affects the arms more than the legs; anterior cord spares proprioception; Brown-Sequard is ipsilateral motor and proprioception loss with contralateral pain and temperature loss; syringomyelia gives dissociated cape sensory loss; tabes gives sensory ataxia and lightning pains.
• ALS is the classic mixed UMN and LMN disease without sensory change.
• Urgent referral is needed for cauda equina, compression and progressive weakness; riluzole 50 mg twice daily is the evidence-based drug for ALS in the AAN and NICE pathways.
• Tabes is treated with intravenous penicillin for 10 to 14 days, and guidelines differ on the value of adjunctive regimens.

Read next, once available, in plain text (not yet linked): neurological examination and localisation; spinal cord compression and myelopathy; aphasias and cortical syndromes; amyotrophic lateral sclerosis; peripheral neuropathy and Guillain-Barre syndrome.