Motor Neuron Disease Overview

Motor neuron disease refers to a group of rare neurodegenerative diseases in which motor nerves in the spine and brain lose function over time. Early signs of motor neuron disease include weakness and slurred speech.

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 the symptoms usually appear after the age of 50 years. It affects more males than females. The most common type of MND is amyotrophic lateral sclerosis (ALS).

The renowned English physicist Stephen Hawking lived with ALS for many decades until his death in March 2018. The American baseball player, Lou Gehrig, also had ALS. This resulted in people calling it Low Gehrig’s disease.


Types of Motor Neuron Disease

There are several types of MND. Doctors classify them according to whether they are hereditary or not, and which neurons they affect. The types include:

  • ALS: This is the most common type of MND. It affects both the upper and lower motor neurons — the neurons in the brain and spinal cord — which then affects the muscles of the arms, legs, mouth, and respiratory system. On average, people with ALS live for 3–5 years after receiving the diagnosis, but with supportive care, some people live for 10 years or longer.
  • Primary lateral sclerosis: This affects the neurons in the brain. It is a rare form of MND that advances more slowly than ALS. It is not fatal, but it can affect the quality of life. Juvenile primary lateral sclerosis occurs in children.
  • Progressive bulbar palsy (PBP): This involves the brain stem, and people with ALS often have PBP, too. It causes frequent choking spells and difficulty speaking, eating, and swallowing.
  • Spinal muscular atrophy (SMA): This inherited MND develops in children. There are three types, all caused by a genetic change known as SMA1. It tends to affect the trunk, legs, and arms. The long-term outlook depends on the type. 
  • Progressive muscular atrophy: This type of MND is rare. It affects the lower motor neurons in the spinal cord and causes slow but progressive muscle wasting, especially in the arms, legs, and mouth.


Causes of Motor Neuron Disease

Motor neurons instruct the muscles to move by passing on signals from the brain. They play a role in both conscious and automatic movements, such as swallowing and breathing.

Experts believe that around 10% of MNDs are hereditary. The other 90% develop randomly.

The exact causes are unclear, but the National Institute of Neurological Diseases and Stroke reports that genetic, toxic, viral, and other environmental factors may play a role.


Signs and Symptoms of Motor Neuron Disease

The different types of motor neuron disease  cause similar symptoms and have three stages: early, middle, and advanced. The diseases progress at different speeds and vary in severity.

Early stage signs and symptoms

In the early stage of MND, symptoms develop slowly and can resemble those of other health conditions. The specific symptoms depend on the type of MND and the area of the body it affects.

Typical symptoms begin in one of the following areas:

  • Arms and legs
  • Respiratory system
  • The mouth

    They can include the following: 

  • A weakening grip, which makes it hard to pick up and hold things 
  • Clumsiness and stumbling
  • Difficulty swallowing (Dysphagia)
  • Fatigue
  • Inappropriate emotional responses, such as laughing or crying 
  • Muscle pains, cramps, and twitches
  • Slurred speech 
  • Trouble breathing or shortness of breath
  • Weakness in the arms and legs
  • Weight loss, as muscles lose their mass

Middle Stage Signs and Symptoms

As the condition progresses, the early symptoms become more severe. People may also experience:

  • Changes in personality and emotional states 
  • Difficulty moving
  • Drooling, due to problems with swalloing
  • Joint pain
  • Muscle shrinkage
  • Uncontrollable yawning, which can lead to jaw pain

A 2017 study suggests that up to half of people with ALS experience brain involvement, including memory and language problems. It also reports that around 12–15% of people with ALS develop dementia. Some patients also experience anxiety, depression and insomnia.

Advanced Stage Signs and Symptoms

Eventually, a person with advanced ALS needs help moving, eating, breathing, or a combination of these. The disease can become life threatening, and breathing problems are the most common cause of death.


Diagnosis of Motor Neuron Disease

Doctors often find it difficult to diagnose motor neuron disease in the early stages, as it can resemble other conditions, such as multiple sclerosis (MS)

If a doctor suspects that someone has MND, they will refer them to a neurologist, who will take a medical history and do a thorough examination. They may also ask for tests, such as:

  • Blood and urine tests: These can help rule out other conditions and detect any rise in creatinine kinase, a substance that muscles produce when they break down.
  • MRI brain scan: An MRI cannot detect MND, but it can help rule out other conditions, such as a stroke, a brain tumor, or unusual brain structures.
  • Electromyography (EMG) and nerve conduction study (NCS): An EMG measures the amount of electrical activity in muscles, while an NCS measures the speed at which electricity moves through muscles.
  • Spinal tap, or lumbar puncture: A doctor takes a sample of cerebrospinal fluid, which surrounds the brain and spinal cord. Analyzing this can help rule out other conditions.
  • Muscle biopsy: This can help detect or rule out a muscle disease.

The medical team monitors the person for some time after the tests before confirming that they have motor neuron disease.

Treatment of Motor Neuron Disease

There is no cure for motor neuron disease, but treatment may slow the progression and maximize the person’s independence and comfort. Medications, supportive devices, and physical therapy can help.

The choice of treatment depends on factors such as:

  • Availability and and affordability of drugs
  • The form of Motor neuron disease
  • Personal needs and wishes
  • Type and severity of symptoms

Slowing disease progression

Drugs appear to be effective at slowing the progression of some types of motor neuron disease. Examples include edaravone (Radicava) for ALS and nusinersen (Spinraza) and onasemnogene abeparvovec (Zolgensma) to treat SMA.

Muscle Cramps and Stiffness

Medications, such as botulinum toxin (Botox), can help. Botox injections can block the signals from the brain to the stiff muscles for about 3 months at a time.

Baclofen (Lioresal), a muscle relaxer, may help ease muscle stiffness, spasms, and yawning. A doctor can surgically implant a small pump to deliver regular doses to the space around the spinal cord. From there, the drug reaches the nervous system.

Some people may also find that physical therapy helps alleviate cramps and stiffness.

Pain Relief

A non steroidal anti-inflammatory drug, such as ibuprofen (Advil, Motrin), can help with mild to moderate pain from muscle cramping and spasms.

A doctor may prescribe stronger pain relief medications for severe joint and muscle pain in more advanced stages.

Other Options

Scopolamine is a medication that may help with drooling, and the body can absorb it through a patch on the skin. Antidepressants may help with episodes of uncontrollable laughter or crying, which doctors call emotional lability.

Other medications can help specifically with pseudobulbar affect, which is the medical term for sudden spells of laughing or crying. Options include dextromethopan hydrobromide (Neudexta).

Assistive Devices and Therapies

In time, a person may need special devices that help with:

  • Breathing 
  • Communicating 
  • Feeding and swallowing
  • Moving around

Some devices help a person stay independent for longer, while others can extend life. For example, ventilators and feeding tubes can support breathing and nutrition.

Speech and language therapy can also help with communication and swallowing. Physical and occupational therapy can help a person maintain mobility and function and find new ways to do specific tasks.

Risk Factors of Motor Neuron Disease

Motor neuron disease can develop in adults or children, depending on the type. These diseases are more likely to affect males than females. Inherited forms may be present at birth. However, MND symptoms are most likely to appear after the age of 50 years.

The different types appear to have some different risk factors. SMA, for example, is always hereditary, but this is not true for all forms of MND. Around 10% of ALS cases in the United States are hereditary.

Also, the National Institute of Neurological Diseases and Stroke observes that veterans appear to have a 1.5 to 2.0 times higher chance of developing ALS than nonveterans. This may indicate that exposure to certain toxins increases the risk of ALS.

In addition, a 2012 study found that professional football players have a higher risk of dying from ALS, Alzheimer’s disease, and other neurodegenerative diseases, compared with other people. Experts think that this could indicate a link with recurrent head trauma.

Outlook

The outlook for people with MND varies widely, depending on the type of the disease.

People with SMA, for example, can expect to have a typical lifespan. Other types of MND can reduce life expectancy.

Emerging medications may help slow the progression of MND. Researchers are also investigating how to use stem cells to repair related damage in the hope of one day producing a cure.

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