Motor neurone disease, also known as amyotrophic lateral sclerosis (ALS), occurs when specialist nerve cells in the brain and spinal cord called motor neurones stop working properly. This is known as neurodegeneration. Motor neurones control important muscle activity, such as:
As the condition progresses, people with motor neurone disease will find some or all of these activities increasingly difficult. Eventually, they may become impossible. It's not clear what causes motor neurones to stop working properly. In about 5% of cases there's a family history of either motor neurone disease or a related condition called frontotemporal dementia. This is known as familial motor neurone disease. In most of these cases, faulty genes have been identified as making a major contribution to the development of the condition.
There's no single test to diagnose motor neurone disease and diagnosis is based mainly on the opinion of a brain and nervous system specialist (a neurologist). The diagnosis of motor neurone disease is usually clear to an experienced neurologist, but sometimes specialised tests are needed to rule out other conditions with similar features. Read more about the causes of motor neurone disease and diagnosing motor neurone disease.
Progression of symptoms
The symptoms of motor neurone disease begin gradually over weeks and months, usually on one side of the body initially, and get progressively worse. Common early symptoms include:
- A weakened grip, which can cause difficulty picking up or holding objects.
- Weakness at the shoulder that makes lifting the arm difficult.
- A "foot drop" caused by weak ankle muscles.
- Dragging of the leg.
- Slurred speech (dysarthria).
The condition isn't usually painful. As damage progresses, symptoms spread to other parts of the body and the condition becomes more debilitating. Eventually, a person with motor neurone disease may be unable to move. Communicating, swallowing and breathing may also become very difficult. In up to 15% of cases, motor neurone disease is associated with a type of dementia that can affect personality and behaviour. This is called frontotemporal dementia, and is often an early feature when it occurs in motor neurone disease. The affected person may not realise that their personality or behaviour is different.