Motor neurone disease (MND) causes a range of symptoms. You may be diagnosed with a type of MND based on how your symptoms present to doctors and other health professionals.
The term MND is used as an umbrella term to help describe the different types, or the “family of motor neurone diseases”. The differences are mainly to do with what parts of the body are affected, and how the disease progresses. The four main types of MND are described below. Each type is not a completely different disease, but rather a different form.
Over time, as symptoms and the rate at which they progress become clearer, your diagnosis may be reviewed and changed to another type.
What all kinds of MND have in common is that they damage the nerve cells in the brain and spinal cord, known as motor neurones or motor nerve cells.
In MND, the nerves weaken and start to die, which means messages can no longer travel between the brain and the muscles. Gradually, with lack of use, muscles get weaker and waste away.
The speed at which MND progresses varies from one person to another.
The information below includes details about how different parts of the body are affected by MND, life expectancy and related neurological diseases.
There are two main types of motor neurones. The two types work together to relay messages between the brain and muscles. The two types are:
Determining the type of MND you have can take some time. There is no one test for MND and it can be difficult to diagnose. A neurologist will look at your symptoms for clues in figuring out which neurones are involved. It takes time to figure out the type of MND because it’s a complex disease, and it requires careful observation and testing of symptoms.
ALS is the most common form of MND and affects both upper and lower motor neurones. ALS is characterised by muscle weakness and stiffness and over-active reflexes. Usually, ALS leads to:
ALS is the umbrella term commonly applied to MND outside Australia and the United Kingdom. It is also known as Lou Gehrig’s disease in the USA and some other parts of the world. ALS is life limiting with a life expectancy of around two to five years after diagnosis.
Like ALS, PBP affects both upper and lower motor neurones but usually affects speech and swallowing muscles first. PBP often presents as slurring of speech or difficulty swallowing. Over time, PBP spreads to affect other muscle groups in the body, such as the arms and legs. PBP is life limiting and expectancy is between six months and three years from onset of symptoms.
In PMA lower motor neurones only are affected and typically individuals with PMA have a slower rate of progression.
PMA may begin in the arms (flail arm type) or the legs (flail leg type).
The lower motor neurone signs include:
PMA can be difficult to diagnose. Recent studies suggest that many people diagnosed with PMA subsequently develop issues with upper motor neurones. Development of issues with upper motor neurones would lead to a reclassification to ALS.
PMA is life limiting but life expectancy is usually more than five years.
PLS is very rare and affects only the upper motor neurones. PLS can present in similar ways to other types of MND. Initial symptoms of PLS can vary, but may include problems with balance, stiffness and weakness of muscles (particularly in the legs), slurring of speech, muscle spasms and cramps.
PLS progresses slowly and life expectancy can be 10-20 years or more.
A small proportion (5-15%) of people with MND will receive a diagnosis of ‘motor neurone disease with frontotemporal dementia’ or MND/FTD.
Often, the symptoms of dementia precede the motor symptoms, sometimes by a number of years.
Dementia is not one specific disease, but refers to a collection of symptoms that are caused by disorders affecting the brain. Dementia affects thoughts, behaviour and the ability to do everyday activities.
MND/FTD is life limiting.
Kennedy’s Disease is a rare kind of inherited disease that affects the upper motor neurones in the brain. The disease is not a type of MND but has similar symptoms.
The disease causes the muscles of the face and limbs to become weaker and waste away. Other major Kennedy’s disease symptoms include enlargement of breasts, muscle cramps and spasms, hand tremors, impotence and speech and swallowing difficulties.
Age of onset is usually between 35 and 40 years and men are mostly affected. The symptoms can be managed and the disease is not usually life limiting, but there is no cure.