Nerve & Muscle Disorders

Nerve & Muscle Disorders

Background

The nervous system is traditionally thought of as having two sub-divisions. The central nervous system, ie the brain and the spinal cord and the peripheral nervous system which would include the pathway of the nerves as they exit from the spinal cord all the way to the muscle itself. The distinction is important as a ‘scan’ will often not detect the cause of a peripheral nervous system disorder and more specialist blood tests and electro-diagnostic testing (neurophysiology or EMG nerve conduction studies) is required.

With the exception of disorders of the nerve muscle junction, the causes of peripheral nerve and muscle disorders are vast. It is not possible in this space to provide specific details on each and every nerve/muscle disorder but rather I have tried to provide a broad outline to my approach to diagnosis in this group of patients.

Further information may be found on the Quick Links webpage.

Peripheral Nerve Disorders

The nerve may be affected anywhere from the point in exits the spinal cord (nerve root) to the plexus or nerve trunk, leading on to the distal or peripheral part of the nerve. The most important step is trying to localise where the problem in the nerve lies and after this trying to work out what the cause of this may be. In order to do this it is crucial that a careful assessment is taken of the medical history before performing a neurological examination as the type of nerve disorder suspected will influence the type of investigations that may be required. For example if one suspects that the nerve root is impinged from a prolapsed disc, then a MRI scan of the relevant part of the spine may be arranged. If however one suspects that the nerve is being affected more distally, perhaps at the wrist in carpal tunnel syndrome, then EMG/nerve conduction studies may be requested (see below). For some forms of neuropathy (small fibre) the standard tests may be normal and diagnosis requires clinical suspicion/acumen!

Common patterns of nerve involvement include entrapment and a condition known as peripheral neuropathy. Peripheral neuropathy is commonly seen when the nerves are affected uniformly in a length dependant process starting with alteration in sensation or power in the feet and progressing over time up the leg and ultimately to the hands. The rate of progression may vary considerably and depends on the cause. Treatments are based on trying to tackle the underling causes. Sadly there is no therapy to simply make the ‘nerves grow back’ and in many patients where the cause is not identified then the treatments are symptomatic or palliative in nature (eg trying to prevent further harm as a result of the neuropathy such as falls or foot ulcers).

Peripheral neuropathy is commonly seen as a result of underlying medical disorders (in particular diabetes), secondary to particular medications or drugs/alcohol and vitamin deficiencies and more rarely due to inherited disorders, or as a sequelae of infections. There are well over a 100 causes of peripheral neuropathy and coming to the diagnosis needs a stepwise and systemic approach that needs to be guided by the individual patient’s symptoms, medical history and physical signs.


For more information about neuropathy see my Quick Links webpage

Motor Neuron Disease (also known as ALS)

This is a very rare and extremely serious disorder affecting the motor nerve usually both in the central and peripheral nervous system. This disorder typically presents in middle age to older adults with weakness progressing over months. The weakness is usually asymmetrical and with the exception of the eye muscles can affect any part of the body including speech, swallowing, respiration as well as the limbs and face/neck. It may cause muscle twitches, cramps and spasms but this disorder does not usually affect sensation or bladder/bowel control. Sadly this condition is progressive and results in a reduced life expectancy, but there are a few patients, especially where just the distal limbs are involved, who may have a better prognosis and survive for 10 years or longer. Motor neuron disease treatment with Riluzole only prolongs life by a few months and in my opinion there is greater benefit to the quality of life via a Multi-Disciplinary Team (MDT) approach made up of Specialist Nurses, Therapists, Palliative Care, Respiratory and Gastroenterology Physicians in conjunction with local patient and Carer Support Groups and charities (MND Association). Together with my colleagues Dr Basil Ridha and Professor Nigel Leigh, I provide Clinical Leadership to such MDT teams based in North West Sussex and Brighton and Hove.

Many patients who fear that they have motor neuron disease will have a benign explanation for their symptoms and motor neuron disease rarely manifests with generalised fatigue or muscle twitches in isolation. The diagnosis of motor neuron disease is only made where there are clear physical signs of progressive upper or lower motor neuron disturbance with muscle weakness, wasting and/or spasticity. Even where there are suggestive physical signs, some patients who are initially suspected as having motor neuron disease turn out to have other neurological conditions. As there are a few treatable disorders that may mimic the symptoms of motor neuron disease, my approach is focused on excluding any potentially treatable disorder before coming to a diagnosis of motor neuron disease. In situations where I am not certain of the diagnosis, or where patients wish to participate in clinical trials, I have referred such patients to the Specialist Motor Neuron Disease Clinic at Hurstwood Park, which is led by my previous mentor Professor Nigel Leigh.

For more information about motor neuron disease see my Quick Links webpage

Muscle Disorders

Muscle disorders typically manifest as weakness. Where there is a lot of fatigue or pain but very little weakness then other disorders may be suspected (eg chronic fatigue syndrome, polymyalgia or fibromyalgia). Like peripheral nerve disorders there are many causes of muscle weakness or ‘myopathy’. Where an underlying inherited or genetic disorder is suspected one may use the term ‘dystrophy’. The clue to a dystrophy may be a positive family history of similar symptoms, or a very slowly progressive muscle disorder starting in a younger patient with no other cause for the weakness being identified. Sometimes muscle disorders may also be suspected with unusual symptoms such as painful cramps or very dark urine after exertion.

A clue to the presence of an underlying muscle disorder can be shown in a blood test with a raised muscle enzyme called creatine kinase or CK. However, the actual CK level can vary between normal individuals and can rise after muscle injury or vigorous exercise. The CK may even be normal in long standing muscle disorders or slightly elevated in some peripheral nerve disorders so it does need to be interpreted with caution!

There are many causes of muscle weakness relating to drugs, alcohol and medication taken, underlying medical (esp endocrine) disorders and even sometimes as a result of infections.

My initial approach is to take a careful history to try and exclude these disorders before considering a primary muscle disorder. The physical examination may sometimes give a clue to the type of muscle disorder. This includes not just the pattern of weakness but also looking for other associated features such as skin rash or joint swelling. Some muscle disorders may also affect the cardiac muscles and muscles of respiration and swallowing and cardiac and respiratory tests may need to be arranged in selected circumstances.

The muscles can be assessed by a neurophysiological test known as electromyography or EMG. Occasionally if no diagnosis is forthcoming and the muscle disorder appears to be progressing I may need to organise a muscle biopsy, this can be done as a day case procedure at Hurstwood Park or patients may be referred to one of the Specialist Muscle Disorders Clinics in Southampton or London.

For more information muscle disorders including Muscular Dystrophy see my Quick Links webpage

Myasthenia Gravis

Myasthenia Gravis is a disorder of the neuro-muscular junction. In other words a disorder of the transmission of the impulse between the nerve and muscle. Myasthenia gravis is rarely due to a congenital abnormality in the receptor structure; and much more commonly due to an acquired auto-immune disorder where the body produces anti-bodies which block transmission at the neuro-muscular junction. Myasthenia though more likely to occur in younger women not infrequently can occur in men and more elderly patients. The symptoms of myasthenia are very variable from patient to patient, but typically cause a painless fluctuating weakness which may be restricted to the eyes (causing double vision and/or drooping eye lids) or may be more widespread affecting particularly the muscles of speech, swallow, face, neck, spine and upper arms. Usually the weakness is more apparent after heat and exertion and improves with rest, for example feeling at one’s best first thing in the morning after waking from sleep.

Other neurological conditions can sometimes present in this fashion and thus the diagnosis does need to be confirmed with blood tests, neurophysiology and other tests.

Myasthenia does not cause pain, sensory symptoms, problems with concentration or thinking and the physical signs and the pattern of fatigue are very different to that manifest by patients with chronic fatigue syndrome.

There are a number of treatments for this condition (see quick web link page) and most patients symptoms can be controlled with medication. A few patients may require surgery to a gland in the neck, sitting just beneath the thyroid, called the thymus gland.

It is important for patients with this condition to make other medical professionals they may encounter aware of their disorder as a number of drugs, anaesthetic agents and other medical problems can make the symptoms much worse. It is for this reason that I advise patients with myasthenia to wear Medical-Alert Bracelets. It is also important for patients to be aware that if they develop progressive symptoms of difficulty with swallowing, or worsening breathlessness that they should seek immediate medical attention (this is known as a ‘myasthenic crisis’).

For more information about Myasthenia Gravis see my Quick Links webpage

What do EMG/Nerve Conduction Studies Involve?

For patients who see me in Sussex, these tests can only be performed at Hurstwood Park Neurological Centre in Haywards Heath.

EMG stands for electromyography and this involves taking electrical recordings from the muscle. This is done by placing a small needle into selected muscles and getting the patient to relax and then contract that muscle. The electrical activity generated by the muscle can be seen both on the screen as well as heard (by converting the electric impulses into sound). This provides information not only on the muscles but also on the nerve supply to the muscle.

The nerve may be stimulated electrically at one end with a recording electrode at the other end to look at the nerve itself. Usually a small electric shock is administered (which may elicit a muscle twitch) and the speed and amplitude of the resulting nerve impulse is measured, thereby giving an indication of the health of the nerve.

Some patients find the above procedures do cause mild discomfort but the vast majority of patients undergo the examination without any problems. The procedure itself is considered to be safe with no known lasting side effects, but it is important that you make the Neurophysiologist aware if you are needle phobic or on any medication which may result in easy bruising (such as Warfarin).

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