Dr James Chapman, Consultant Neurologist, JCUH
Introduction
Spinal cord dysfunction is a common neurological problem. When it is acute it also is considered a medical emergency. Given this, it is one of the main neurological presentations that all doctors should be able to recognise and at least initiate investigation.
Presentation
At its simplest a spinal cord lesion presents with neurological dysfunction below the level of the lesion. In reality the lesion may be a couple of spinal levels away from the symptomatic level. The symptoms often include weakness, sensory disturbance and bowel/bladder dysfunction. They tend to be bilateral but not necessarily symmetrical and not every patient will have all of these. That said a patient presenting with symptoms in both legs and urinary retention should ring alarm bells.
Neurology is often thought to be very difficult or complicated. The vast majority of a neurologist’s job is to do the basics well and follow simple rules to aid diagnosis. We tend to split presentations up in a variety of ways to help narrow down a differential diagnosis.
One way is by speed of onset: Hyperacute (seconds to minutes); Acute (hours to days); Sub-acute (days to weeks); Chronic (weeks to months or even years). These categories are a strong pointer towards possible underlying causes.
Another way is by what symptoms and signs the patient presents with. This requires a bit of knowledge of anatomy.
Essentially, motor fibres are anterior and lateral in the spinal cord. By the time they enter the top of the spinal cord, they have already crossed. This means that, if the left leg is weak clinically, then the spinal lesion will be on the ipsilateral side.
Sensory fibres are split, with vibration and proprioception posteriorly and pain and temperature anteriorly. This spread of different modalities allows for different spinal cord syndromes that can be helpful in localisation of a lesion and differential diagnosis.
Extrinsic Compression
A lesion compressing the spinal cord causes weakness and sensory disturbance below the level of the lesion and sphincter disturbance. The sacral dermatomes are usually affected as they lie close to the surface in the spinal cord. A slowly compressive lesion therefore will affect lower dermatomes and the sensory level will ascend as compression worsens and deeper fibres become involved.
A sensory level is therefore the lowest spinal level the lesion can possibly be – the lesion may be much higher than this depending on the degree of compression.
Aside from the sensory level, the clinical signs include anything from mild to complete paresis of the lower limbs, and possibly the upper limbs, depending on the location of the lesion. There are usually upper motor neuron signs (hyperreflexia, spasticity etc) in the lower limbs. In the upper limbs, there may be a confusing mix of lower motor neuron (absent reflexes, reduced tone, wasting etc) and upper motor neuron signs, depending on where the lesion is. There may also be local pain or radicular pain from irritated nerve roots.
The basic TeesNeuro rule of thumb is that you can always think the lesion is too low, but you can never think it is too high. This is of practical importance when ordering scans – too low and you will miss it.
Acute Complete Lesions
These produce an extreme version of the symptoms seen in extrinsic compression, with all sensory and motor function below the lesion lost. There may also be “spinal shock”, which can last days or weeks. This consists of paradoxical lower motor neuron signs and autonomic dysfunction.
Anterior Cord Syndrome
If we think about the anatomy described above, then a lesion of the anterior cord will involve motor tracts in addition to spinothalamic tracts (pain/temperature sensation). This will spare the dorsal columns (proprioception/vibration). There are a few causes of this syndrome, but the spinal cord infarct is the commonest and most typical.
A spinal cord infarct is hyperacute in onset and usually very painful. The posterior cord has its blood supply from two spinal arteries. The anterior cord via only one, hence its vulnerability. The artery of Ademkiewicz is particularly vulnerable as a segment direct from the aorta. It supplies much of the lower spinal cord usually below T9.
One rare cause to be aware of is an aortic dissection compromising the anterior spinal artery.
Beware the patient with chest pain and leg weakness.
Central Cord Syndrome
Sometimes a lesion may disproportionately affect the central grey matter of the spinal cord, with relative sparing of the long tracts (e.g. motor and sensory supply to the lower limbs etc). This can occur in the context of trauma and is more likely if there is a degree of pre-existing spinal cord compressions e.g. from degenerative spinal disease. Another typical cause is syringomyelia (a syrinx) which is a fluid filled cavity that can form in the spinal cord usually in the cervical cord but can extend. This is usually associated with a Chiari malformation.
Clinically the patient will have lower motor neuron signs in the upper limbs but may have preserved lower limb function until very late. The sensory loss is variable but often can disproportionately affect the patient’s hands with numb, painful and clumsy hands. In syringomyelia there is typically a suspended cape like loss of pain and temperature sensation as these fibres are affected as they decussate in the ventral white commissure.
Posterior Cord Lesion
This can result from vascular damage, but more often is caused by ametabolic insult such as Vitamin B12 deficiency. This results in loss of dorsal column function (proprioception/vibration sense), but preservation of pain and motor function. The loss of proprioception can be extremely debilitating leaving a patient ataxic, and if severe, with inability to walk.
Hemi-cord syndrome
A lesion can affect half of the spinal cord, sparing the other half. This can produce the typical features of a Brown-Sequard syndrome. It is relatively rare for this syndrome to be complete.
The syndrome consists of motor and dorsal column function loss on the side of the lesion and spinothalamic sensory loss on the contralateral side. This dissociated sensory disturbance is as a result of the spinothalamic tract decussating near its dermatome rather than at the level of the brain stem as for dorsal column and motor tracts.
High Cervical or Foramen Magnum Lesions
These can produce a confusing clinical picture. They can present in a “round the clock” fashion, with one arm being affected first before spreading to the ipsilateral leg, contralateral leg and finally the contralateral arm. There can be lower motor neuron signs distally in the upper limbs despite the lesion being above the myotome for these areas.
Conus Lesion
A lesion of the conus can produce mixed upper motor neuron and lower motor neuron signs in the lower limbs. Typically, this is associated with profound sphincter disturbance and saddle anaesthesia. There are usually absent ankle jerks but with up-going plantar responses.
Cauda Equina
This is the one we have drilled into us at medical school and are anxious to never miss. As as result, it is often the only thing people try to rule out, missing all the other important stuff en route.
Usually, the cause is degenerative disease of the low lumbar or high scaral spine. An L4/5 disc prolapse, for example, could easily cause cause cauda equina.
Remember, at this level, the spinal cord no longer exists – it’s just a load of nerve roots (peripheral nerves that haven’t escaped yet) and so any signs will be “lower”. If you ever see a patient with obvious “upper” signs, it cannot be cauda equina by definition (so look higher).
With an L4/5 lesion, we might see a numb bum (saddle anaesthesia), incontinence (bladder and bowel) and distal weakness in the legs. It may or may not be painful, but often is.
This is an emergency and requires an MRI scan immediately. Ask your senior if you are unsure.
Spinal Roots
The spinal nerve roots exit as a ventral and a dorsal root, then combine to form mixed sensorimotor spinal nerves. They are numbered for the adjacent vertebrae. In the cervical spine the spinal nerves are named for the vertebra below it (e.g. C6 nerve emerges from the C5/6 junction). As there are only 7 cervical vertebra but 8 spinal nerves the 8th emerges between the junction of C7 and T1. Below this level all spinal nerves are numbered for the vertebra above (e.g. T4 emerges from the T4/5 junction).
A lesion affecting a spinal root (such as a “slipped disc”) tends to be painful locally, but also along its dermatome. There may also be sensory or motor dysfunction in the areas innervated by the nerve.
Differential Diagnosis
As we have seen above, the clinical presentation can be divided by localisation and speed of onset. These factors can direct a differential diagnosis, but there are a multitude of other factors in the history and from investigations that can contribute. Going through all of these is beyond the scope of this resource.
Common causes of spinal cord neurological presentations have briefly been mentioned above. These include but are not exclusive to: spinal cord infarct, trauma, degenerative spinal disease, inflammatory (e.g. MS, NMO etc), metabolic (e.g. B12), neoplastic, paraneoplastic, infection and genetic.
A good starting point is to think of intrinsic and extrinsic problems and then use your “sieve”. Extrinsic are strucutral (disc prolapse, tumour, haematoma, abscess etc.) and intrinsic can be manifold (tumour, infarct, infection, metabolic etc.)
Beyond the clinical aspects discussed, the investigations help direct, and this can include many factors such as the length of a spinal cord lesion on MRI, lumbar puncture and blood tests.
A basic investigation screen should include imaging of the lesion, for instance with MRI of the appropriate part of the spine; a routine blood test screen (FBC, UE, LFT’s, B12, ESR); a more specific blood test screen (this is quite variable case to case but can include HIV, syphilis, copper, specialist antibody tests such as aquaporin 4 antibodies or very long chain fatty acids) and further imaging of other parts of the nervous system.
Below are a couple of flow charts that are overly simplified and not exhaustive. They serve as a useful tool to guide further thought where MRI has revealed a cord lesion that is not related to degenerative disease or trauma.
Leg Weakness
Leg weakness is often caused by lesions in the spine. This is not the only cause of leg weakness, so you must keep an open mind. Many of the other causes of leg weakness will be covered in other areas and are outside the scope of this resource.
For isolated single leg weakness don’t forget stroke.
For bilateral don’t forget peripheral neuropathy or myopathy.
Motor neurone disease can also mimic spinal disorders or be mimicked by them in turn.