Motor neurons are nerve cells that send electrical output signals to the muscles, affecting the muscles' ability to function.
Motor neuron disease (MND) can appear at any age, but most patients are over 40 years old at diagnosis. It affects men more than women.
The renowned English physicist, Stephen Hawking, and guitar virtuoso Jason Becker have been living with ALS for several years.
Contents of this article:
Fast facts on motor neuron diseases
Here are some key points about motor neuron diseases. More detail is in the main article.
- Motor neuron diseases (MND) are a group of conditions that affect the nerve cells that send muscles to the brain.
- There is a progressive weakening of all the muscles in the body, which eventually affects ability to breathe.
- Genetic, viral, and environmental issues may play a role in causing MND.
- There is no cure, but supportive treatment can improve the quality of life.
- Life expectancy after diagnosis ranges from 3 years to longer than 10 years.
- British scientist Stephen Hawking has lived with MND for many years.
Types of motor neuron disease
Stephen Hawking is one of the most well-known people with a motor neuron disease.
Image credit: Doug Wheller, 2008
There are several types of motor neuron disease.
ALS, or Lou Gehrig's disease, is the most common type, affecting muscles of the arms, legs, mouth, and respiratory system. Mean survival time is 3 to 5 years, but some people live 10 years or more beyond diagnosis with supportive care.
Progressive bulbar palsy (PBP) involves the brain stem. People with ALS often have PBP too. The condition causes frequent choking spells, difficulty speaking, eating, and swallowing.
Progressive muscular atrophy (PMA) slowly but progressively causes muscle wasting, especially in the arms, legs, and mouth. It may be a variation of ALS.
Primary lateral sclerosis (PLS) is a rare form of MND that advances more slowly than ALS. It is not fatal, but it can affect the quality of life. In children, it is known as juvenile primary lateral sclerosis.
Spinal muscular atrophy (SMA) is an inherited MND that affects children. There are three types, all caused by an abnormal gene known as SMA1. It tends to affect the trunk, legs, and arms. Long-term outlook varies according to type.
The different types of MND share similar symptoms, but they progress at different speeds and vary in severity.
Signs and symptoms
MND can be divided into three stages, early, middle, and advanced.
Early stage signs and symptoms
Symptoms develop slowly and can be confused with symptoms of some other unrelated neurological conditions.
Early symptoms depend upon which body system is affected first. Typical symptoms begin in one of three areas: the arms and legs, the mouth (bulbar), or the respiratory system.
- a weakening grip, making it hard to pick up and hold things
- muscle pains, cramps, and twitches
- slurred and sometimes garbled speech
- weakness in the arms and legs
- increased clumsiness and stumbling
- difficulty swallowing
- trouble breathing or shortness of breath
Middle stage signs and symptoms
Motor neuron diseases can leave those with the disease severely restricted in mobility.
As the condition progresses, symptoms become more severe.
- Muscle pain and weakness increase, and spasms and twinges worsen.
- Limbs become progressively weaker.
- Limb muscles start to shrink.
- Movement in affected limbs becomes more difficult.
- Limb muscles may become abnormally stiff.
- Joint pain grows.
- Eating, drinking, and swallowing become harder.
- Drooling occurs, due to problems controlling saliva.
- Yawning occurs, sometimes in uncontrollable bouts.
- Jaw pain may result from excessive yawning.
- Speech problems worsen, as muscles in the throat and mouth become weaker.
The person may show changes in personality and emotional state, with bouts of uncontrollable crying or laughing.
Previously, it was believed MND did not significantly affect brain function or memory, but studies have now shown that up to 50 percent of people with ALS have some type of brain function involvement.
Breathing problems may occur as the diaphragm, the main breathing muscle, deteriorates. There may be a shortage of breath, even when sleeping or resting. Ultimately, breathing assistance will be necessary.
Advanced stage signs and symptoms
Eventually, the patient will be unable to move, eat, or breathe without assistance. Without supportive care, an individual will pass away. Despite the best of care currently available, complications of the respiratory system are the most common causes of death.
Causes and risk factors
Motor neurons send signals from the brain to the muscles and bones, and this makes the muscles move. They are involved in both conscious movements and automatic movements, such as swallowing and breathing.
Some MNDs are inherited while others happen randomly. The exact causes are unclear, but the National Institute of Neurological Diseases and Stroke (NINDS) notes that genetic, toxic, viral, and other environmental factors likely play a role.
Heredity: In the United States (U.S.), around 1 in every 10 cases of ALS is inherited. SMA is also known to be an inherited condition.
Age: After the age of 40 years, the risk rises significantly, although it is still very small. ALS is most likely to appear between the ages of 55 and 75 years.
Sex: Men are more likely to develop an MND.
Some experts have linked military experience to a higher chance of developing the disease.
Studies have found that professional footballers are more likely to die from ALS, Alzheimer's disease, and other neurodegenerative diseases, compared with other people. This implies a possible link with recurrent head trauma and neurological disease.
The treatment of motor neuron diseases is mostly about managing symptoms and enabling comfortable living.
A primary care physician will normally refer the patient to a neurologist, a doctor specialized in the diagnosis and treatment of diseases and conditions of the nervous system.
The neurologist will start with a complete history and physical exam of the neurologic system.
Other tests may be helpful.
Blood and urine tests: These analyses can rule out other conditions and detect any rise in creatinine kinase. This is produced when muscle breaks down, and it is sometimes be found in the blood of patients with MND.
Electromyography (EMG) and nerve conduction study (NCS): These are often performed together. An EMG tests the amount of electrical activity within muscles, while NCS tests the speed at which electricity moves through muscles.
Spinal tap, or lumbar puncture: This analyzes the cerebrospinal fluid, the fluid that surrounds the brain and spinal cord.
Muscle biopsy: If the doctor thinks the patient may have a muscle disease, rather than MND, a muscle biopsy may be performed.
After tests, a doctor will normally monitor the patient for some time before confirming that they have MND.
Criteria known as El Escorial criteria can help a doctor check for distinctive neurological signs, that may aid in the diagnosis of ALS.
- muscle shrinking, weakness or twitching
- muscle stiffness or abnormal reflexes
- symptoms spreading into new muscle groups
- having no other factors that explain the symptoms
Occupational therapy can help to alleviate some of the stiffness and stress of a motor neuron disease.
There is no cure for MND, so treatments focus on slowing the progression and maximizing patient independence and comfort.
This can include the use of breathing, feeding, mobility and communication appliances and devices.
Rehabilitation therapy may include physical, occupational and speech therapy.
Slowing disease progression
Two drugs are currently approved by the U.S. Food and Drug Administration (FDA) for ALS. Riluzole, or Rilutek, lowers the amount of glutamate in the body. It appears most effective in the early stages of ALS and in older individuals. It has been shown to improve survival.
In early 2017, the drug Radicava (Endaravone) was approved by the FDA for the treatment of ALS.
How it works is not well understood, but it may delay disease progression by working against tissue damage.
Muscle cramps and stiffness
Muscle cramps and stiffness can be treated with physical therapy and medications, such botulinum toxin (BTA) injections. BTA blocks the signals from the brain to the stiff muscles for about 3 months.
Baclofen, a muscle relaxer, may reduce muscle stiffness. A small pump is surgically implanted outside the body and connected to the space around the spinal cord. A regular dose of baclofen is delivered into the nervous system.
Baclofen blocks some of the nerve signals that cause spasticity. It may help with extreme yawning.
Treatment for drooling
Scopolamine, a drug for motion sickness, may help control symptoms of drooling. It is worn as a patch behind the ear.
Uncontrolled laughter or crying
Speech, occupational and physical therapy
Patients with speech and communication difficulties may learn some useful techniques with a qualified speech and language therapist. As the disease advances, patients often need some communication aids.
Physical and occupational therapy can help maintain mobility and function, and reduce stress.
Swallowing difficulties (dysphagia)
As eating and drinking become harder, the patient may need a percutaneous endoscopic gastrostomy (PEG), a feeding tube that is placed on the abdomen, a relatively minor procedure.
A non-steroidal anti-inflammatory drug (NSAID), such as ibuprofen, will help with mild to moderate pain from muscle cramping as spasms. Drugs such as morphine can help relieve severe joint and muscle pain in the advanced stages.
Respiratory muscles usually weaken gradually, but a sudden deterioration is possible.
Mechanical ventilation can help with breathing. A machine takes in air, filters it, and pumps it into the lungs often through a tracheostomy, a surgical hole in the neck that allows for assisted breathing.
Stem cell transplant for ALS treatment
Stem cell research and gene therapy have shown promise for treating ALS in the future, but more studies are needed.
The United Kingdom's (U.K.) National Health Service (NHS) notes that living with an MND can be extremely challenging, and diagnosis can seem like a "terrifying possibility."
However, they add that with community and other support, the patient's quality of life is often better than expected, and the advanced stage "isn't usually distressing." For most people, this comes at home, while sleeping.
Patients may wish to prepare an advanced directive, in which they can state their future wishes about treatment while they are still able to express themselves.
Issues may include where they hope to be treated in the later stages, for example, in the hospital, in a hospice center or at home with hospice care, and whether they would like to receive mechanical breathing or other assistive care.
As medical research continues, scientists hope to understand MNDs more fully. They are working towards finding new treatments.