Motor neurone disease (MND) is an umbrella term for a group of diseases that affect motor neurons. Motor neurons are the nerve cells in the brain and spinal cord that are responsible for voluntary movement.
In MND, the nerves weaken and start to die. This means messages can no longer travel between the brain and the muscles. Over time, with lack of use, muscles get weaker and waste away.
The speed at which MND progresses varies from one person to another and also depends on which type of MND you have.
The different types of MND are determined by what parts of the body are affected, and how quickly the disease progresses. Each type is not a completely different disease, but a different form.
You may be diagnosed with a type of MND based on how your symptoms originally present. Over time, as symptoms and the rate at which they progress become clearer, the type of MND may be revised.
The information below includes details about motor neurons, which parts of the body are affected by different types of MND and life expectancy.
There are two main types of motor neurons. The two types work together to send messages between the brain and muscles. The two types are:
- Upper motor neurons, which start in the brain. They send messages from your brain to the lower motor neurons in the spinal cord.
- Lower motor neurons, which start in the spinal cord. They connect with your upper motor neurons to send messages to your muscles. The messages tell your muscles to move, walk, swallow, talk and breathe.
Amyotrophic lateral sclerosis (ALS) is the most common form of MND and affects both upper and lower motor neurons. Weak muscles, stiff limbs and overactive reflexes are key features of ALS. It most commonly starts in a limb (arm or leg). ALS will progress over time, to other parts of the body.
Outside Australia and the United Kingdom, ALS is used as the general name for MND. ALS is also known as Lou Gehrig’s disease in the USA and some other parts of the world.
ALS is life-limiting. Life expectancy is around two to five years after diagnosis.
Like ALS, progressive bulbar palsy (PBP) affects both upper and lower motor neurons, but the speech and swallowing muscles are affected first. PBP is sometimes called bulbar onset MND.
Early signs of PBP might include slurred speech, changes in voice quality, or trouble swallowing. Sometimes, in the later stages of PBP, other parts of the body like the arms and legs may become affected.
PBP is life-limiting. Life expectancy is between six months and three years from onset of symptoms.
Progressive muscular atrophy (PMA) is a relatively rare form of MND, and can be difficult to diagnose. In PMA only the lower motor neurons are affected. PMA may begin in the arms (flail-arm type) or the legs (flail-leg type). Common signs include:
- muscle wasting or weakness in the affected limb/s
- weight loss
- significant muscle twitching.
Recent studies suggest that many people who are initially diagnosed with PMA later develop issues with upper motor neurons. They are then reclassified as having ALS.
PMA is life-limiting but typically progress slower than other types of MND. Life expectancy is usually more than five years.
Primary lateral sclerosis (PLS) is very rare and affects only the upper motor neurons. PLS can present in similar ways to other types of MND. Initial symptoms of PLS can vary, but may include:
- problems with balance
- stiff or rigid muscles (particularly in the arms or legs)
- slurring of speech
- muscle spasms and cramps.
PLS progresses slowly and life expectancy can be 10–20 years or more.
A small number of people with MND (5–15%) will receive a diagnosis of ‘motor neurone disease with frontotemporal dementia’. Doctors call this MND-FTD.
Often, the symptoms of dementia arise before the motor symptoms, sometimes by a number of years.
At the start, people may have trouble talking or understanding others’ speech. Changes in personality and behaviour can also occur. To learn more about FTD visit Dementia Australia
MND-FTD is life-limiting.
Kennedy’s disease is a rare inherited disease that affects the lower motor neurons 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 weaken and waste away. 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.
Sources
Information for people with or affected by MND (MND Association UK, 2020)
ALS, MS AND MD: How Do They Differ? (ALS Society of Canada, 2017)
Symptoms and Diagnosis (ALS Association, 2020)
Keep in touch
Get the latest news about MND research,
care & advocacy right in your inbox.