Demyelinating disease

These diseases are a group of disorders in which the myelin sheath surrounding the part of the nerve cells which transmit nervous impulses, the axons, is lost in the central nervous system. This prevents the impulse from travelling between nerves. In this particular group there is also inflammation accompanying the loss of the myelin.

The most common of these diseases is multiple sclerosis. The cause of multiple sclerosis is unknown, but it is possible that a virus is involved in precipitating the disease. It is most common in temperate regions of the world, occurring at a rate of about 10 new cases per 100,000 per year in these areas. The incidence in Australia, New Zealand and the southern United States is one third to one half of that. In Africa, multiple sclerosis is rare.

Multiple sclerosis manifests itself by recurrent attacks of specific neurological deficits, such as problems with vision, problems with speaking, decreased perception of vibration and position sense, an unsteady gait, weakness in one or more limbs, spasticity and bladder problems. The type of neurological deficit depends on where the demyelination is occurring. Classically, optic neuritis (causing symptoms of loss of vision with pain in one eye) is taken as a one of the most common presenting signs of multiple sclerosis, occurring as the first sign in 40% of patients. These neurological deficits occur, remit and recur, at random over many years. The disease most commonly occurs in early adulthood, with the frequency of flare ups most common in the first 3 to 4 years of the illness. However, a very mild first attack, which may not even have resulted in medical attention, may not be followed by another attack for 10 to 20 years. In general, however, there is a stepwise downward progression, with increasing deficit with each attack. The average survival from first attack is 30 years.

In the early stages multiple sclerosis can be difficult to diagnose, since it can mimic other neurological conditions, particularly if the deficits are very specific. MRI scan is the most sensitive means of detecting the characteristic lesions of demyelination, but clinical findings are the most important means of diagnosis, which should only be backed up by further investigations.

There is no curative treatment for multiple sclerosis, and management is aimed at keeping the person as able as possible for as long as possible. Patients should eat a balanced diet and avoid excessive fatigue and extremes of temperature. In the later stages bowel and bladder training are useful. Physiotherapy and occupational therapy play an important role in management, as can speech therapy.

A demyelinating disease of the peripheral nervous system is acute demyelinating polyneuropathy, better known as Guillain-Barré syndrome (GBS). This is an acute condition, frequently severe, which occurs at a rate of one case per million per month, or 3500 cases per year. Incidence patterns are similar world wide. In more than two-thirds of cases, there is a preceding viral infection, frequently with a herpes infection (cytomegalovirus or Epstein-Barr). Five to 10% of cases occur 1 to 4 weeks after surgery. GBS can also occur in association with lymphoma, including Hodgkin's Disease and with SLE.

Guillain-Barré is thought to be an immune mediated disease, but exactly how this happens is uncertain.

Clinically, the patient experiences increasing weakness, leading to paralysis, with some mild sensory disturbance. Most people have to be hospitalised, and a small number will need to be ventilated at some point in the illness. Treatment is generally supportive, although plasmapharesis (effectively cleaning the plasma) seems to decrease the course of the illness, particularly if started in the first 2 weeks.

About 85% of people make a complete or near complete recovery.

Motor neuron disease

Many of you will know, by reputation, the brilliant Cambridge physicist, Steven Hawking, author of the best selling "A Brief History of Time". If any of you have seen him on TV, or as I was lucky enough to, in the Cambridge Union, you will instantly have a picture of what motor neuron disease is all about.

As with many neurological diseases, motor neuron disease is a group of progressive diseases. Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease (after a famous American baseball star), is the most common.

ALS generally starts in late middle age, often after the age of 50. It is rare before the 30s and patients who develop the disease in their teens seem to have an inherited variant of the disease. Men are more frequently affected than women. In about 10% of cases there is a genetic link within families, although this form is actually slightly different clinically and pathologically.

The disease is characterised by a progressive loss of motor neurons, resulting in weakness of the voluntary muscles, including those of speech and vision. It first shows itself as an insidious weakness, usually asymmetrically, in one limb. These muscles are easily tired and subject to cramps. Visible wasting of the muscles can be seen as the weakness progresses. Virtually any muscle group can be the first to develop signs, but with time more and more groups become involved, and eventually there is a symmetrical distribution of weakness in all regions, including the muscles of chewing, swallowing and movements of the face and tongue. If the respiratory muscles are involved early on then an early death may occur. Otherwise, death is generally due to chest infection secondary to profound general weakness.

The course is relentlessly progressive, but the total duration of the illness is variable. About 50% of patients will die within 3 to 5 years after the start of the disease, but, as Steven Hawking has demonstrated, some live considerably longer. Very rarely, ALS may become stabilised or even regress to recovery.

There is no curative treatment for ALS, but modern rehabilitative measures, including mechanical aids and respiratory support, can improve quality of life immensely.

Links

The South African Multiple Sclerosis Society. A South African resource for those suffering from this diseas and for those caring for them.

The Institute of Neurotoxicology and Neurological Disorders has a section on ALS, as has the Doctor's Guide. Both these sites can be searched for other neurological diseases as well.

The National Institute of Neurological Disorders and Stroke is a section of the American National Institutes of Health, and has a wealth of information on neurological diseases in general.

The UK Health Center is an excellent site with a whole section devoted to Web links for patient information.