What is Motor neurone disease?

Motor neurone disease is the name given to a group of related diseases in which there is selective and progressive loss of function of the motor neurones (the motor nerve cells that control movement) in the brain and spinal cord. The motor neurones degenerate leading to weakness and wasting of the muscles that they supply. There are a number of types of motor neurone disease with different clinical presentations and prognoses. The commonest type of motor neurone disease is amyotrophic lateral disease. It is a progressive condition leading to generalised muscle paralysis, for which there is no curative treatment and invariably has a fatal outcome.

Types of motor neurone disease

The disabling effects of motor neurone disease vary depending on which groups of muscles are affected, the speed of the degenerative process and the time of progression to generalised paralysis. Typical clinical presentations are grouped under four headings, though many cases may show features of more than one variety.

Amyotrophic lateral sclerosis

This is the most common type of motor neurone disease seen in 65% of cases. Initially it affects the hands (more commonly) or the feet with wasting and weakness. Later the rest of the limbs become progressively paralysed and difficulties in speaking and swallowing occur. Death is usually due to paralysis of respiratory muscles. 50% of people amyotrophic lateral sclerosis die within three years of onset.

Progressive bulbar palsy

25% of cases present with progressive bulbar palsy, whenthe disease affects predominantly the motor neurones that control the muscles of the face, tongue, palate and the throat. This causes increasing difficulties in talking, chewing and swallowing. These are known as bulbar symptoms. Death is often due to aspiration of food and saliva into the lungs causing pneumonia, and occurs within 1 to 3 years of onset.

Progressive muscle atrophy

In this type of motor neurone disease muscle (less than 10% of cases) wasting and weakness involves the hands at first. The condition progresses to the arms, shoulders and then later to the legs; ultimately paralysis becomes generalised. The progression of this condition is slower than that of the presentations described above. Progressive muscular atrophy can occur at any age, including in childhood. People may survive 25 years or more with this condition.

Primary lateral and progressive pseudo bulbar palsy

This uncommon presentation is seen in 2% of cases. Muscle stiffness and weakness affects the limbs at first and later progresses to affect speech, swallowing etc. Its clinical course is longer in duration than amyotrophic lateral sclerosis or progressive bulbar palsy, and it takes several years before total disability supervenes.

Prevalence and Incidence

The cause of motor neurone disease is unknown, although in a small number of cases there is a hereditary or familial element. It occurs worldwide and has an incidence of 1 – 2 per 100,000 of the population. In the UK it usually occurs in older age groups with symptoms presenting between 50 to 70 years. It is more common in men than women (male: female 3: 2).

Amended June 2008