Motor Neuron Diseases

Medically Reviewed By William C. Lloyd III, MD, FACS
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What are motor neuron diseases?

Motor neuron diseases (MNDs) are a group of neurological conditions that progressively destroy motor neuron cells. Motor neuron cells are critical to health and normal, everyday functioning because they control many voluntary muscle actions, such as swallowing, breathing, speaking, talking, hand gestures, and walking. This is different from sensory nerves that permit you to sense touch, pain and temperature.

Normally, nerve cells in the brain send commands through the spinal cord to muscle nerve cells to perform movements. When nerve cells are damaged or destroyed by a motor neuron disease, muscles cannot receive the brain’s messages. This results in muscle weakening and wasting, fasciculations (uncontrollable twitching), spasticity, and stiffness in the legs and arms.

Amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig’s disease) is the most common motor neuron disease, accounting for approximately 85% of motor neuron disease (Source: CDC).

Other motor neuron diseases include:

  • Post-polio syndrome, also known as PPS, is a syndrome that affects polio survivors decades after recovery from poliomyelitis.

  • Primary lateral sclerosis, also known as PLS, is a rare disease that causes progressive weakness of voluntary muscles.

  • Progressive bulbar palsy is a disease that affects the brain stem causing weakness and problems with swallowing, speaking and chewing.

  • Progressive muscular atrophy is a disease that causes weakness in the hands and lower body.

In most cases, the cause of motor neuron diseases is not known; however, a small percentage of cases are inherited. Some motor neuron diseases, such as ALS, are ultimately fatal, while others, such as PLS, impact bodily functions and quality of life, but do not necessarily result in death. While there is no cure for MNDs, treatments are available that may reduce symptoms and help you live as active a life as possible. These treatments vary depending on the specific underlying disease and the severity of the symptoms.
Seek prompt medical care if you develop problems with muscle function or weakness; difficulty with speaking, swallowing or chewing; muscle spasticity or cramps; clumsiness; or other unexplained symptoms. Early diagnosis and treatment may help slow the progression of the disease and improve your quality of life. Seek prompt medical care if you have been diagnosed with a motor neuron disease and your symptoms worsen or you experience new symptoms.

Seek immediate medical care (call 911) if you, or someone you are with, have serious symptoms or complications of motor neuron disease, such as difficulty breathing or choking.


What are the symptoms of motor neuron diseases?

Symptoms of motor neuron disease (MND) are related to problems with communication between your nerves and muscles. Symptoms of motor neuron diseases vary depending on the specific disease.

Early symptoms of MNDs

You may experience symptoms daily or just once in a while. In the early stages of disease, symptoms may be subtle and include:

  • Changes in voice
  • Difficulty chewing or swallowing
  • Increased reflexes
  • Muscle stiffness or cramps
  • Slowness in voluntary muscle activity
  • Weakness (loss of strength)

    Later symptoms of MNDs

    As the disease progresses over the course of months or a few years, symptoms can plateau or level off, or become increasingly more persistent and severe. Later-stage symptoms of MNDs include:

    Serious symptoms that might indicate a life-threatening condition

    Some motor neuron diseases can cause life-threatening complications. Seek immediate medical care (call 911) if you, or someone you are with, have any type of sudden, severe respiratory or breathing problem such as:

    What causes motor neuron diseases?

    Motor neuron diseases (MNDs) are the result of problems with communication between motor neurons (nerves) and muscles. Normally, nerves in the brain send commands to muscle nerve cells to carry out specific movements. When nerve cells along this chain of command are damaged or destroyed by motor neuron disease, they cannot receive the brain’s messages. This leads to the symptoms of motor neuron diseases, such as muscle weakening and wasting, fasciculations (uncontrollable twitching), spasticity, and stiffness in the legs and arms.

    It is not known what causes the destruction of motor neurons in motor neuron disease; however, some cases of MNDs are inherited and run in families. Some inherited forms of amyotrophic lateral sclerosis (ALS) are caused by mutations in the SOD1 gene, which helps protect your body’s cells from oxidative damage.

    Currently, researchers are investigating factors that may be related to the development of MNDs, such as ALS. These factors include:

    • Abnormally high levels of glutamate, a chemical that passes messages between nerves

    • Defective immune response in which the immune system may attack the nerves that control muscles, leading to a loss of muscle control

    • Environmental factors, such as infections, toxic substances, and dietary deficiencies

    What are the risk factors for motor neuron diseases?

    A few factors increase the risk of developing a motor neuron disease (MND). They include:

    • Age older than 50 years

    • Family history of MND

    • Male gender

    • Personal history of MND; for example, if you have primary lateral sclerosis, you are more likely to develop ALS

    How are motor neuron diseases treated?

    While there is no cure for motor neuron diseases (MNDs), some drug treatments can help reduce the severity of symptoms. One drug, riluzole (Rilutek), may help slow damage to the nerves that control muscles. Other treatments and medical support, such as physical therapy, speech therapy, assisted breathing apparatuses, and home hospice care, are aimed at helping you and your family cope with the progressive lack of muscle control involved with MNDs.

    Medications

    With the exception of riluzole (Rilutek), drugs used to treat MNDs can only reduce or minimize symptoms. Riluzole is prescribed for people with ALS to slow damage to the nerves that communicate with voluntary muscles. Riluzole can prolong life, but it is not a cure for ALS. Drugs prescribed for symptoms of MNDs may include:

    • Anticholinergic drugs, which control the production of saliva and prevent choking

    • Anticonvulsants, which help control nerve pain

    • Antidepressants, which treat depression

    • Benzodiazepines, which treat anxiety and insomnia

    • Decongestants, which help with breathing

    • Muscle relaxants, which control muscle spasms

    • Pain medications, which help control pain

    • Stimulants, which help with fatigue

    Other types of therapy and treatment

    Physical therapy and other therapies may help you and your family cope with the symptoms of MNDs and may extend the time that you are able to perform normal activities. Types of therapy for MNDs include:

    • Digital communication devices that permit eye movements to perform actions similar to a personal computer mouse.
    • Feeding tubes to prevent weight loss and promote proper nutrition, especially in late stages of the disease

    • Home healthcare or hospice care to assist with daily activities

    • Mechanical ventilation to assist you when your breathing is severely affected

    • Nutritional support to prevent weight loss

    • Occupational therapy to assist patients in continuing to work and perform daily functions

    • Physical therapy to improve the ability to use muscles

    • Speech therapy to assist with speaking difficulties

    • Support groups or counseling to help patients and families deal with the emotional consequences of motor neuron disease

    Complementary treatments

    Some complementary treatments may help some people in their efforts to deal with MNDs. These treatments, sometimes referred to as alternative therapies, are used in conjunction with traditional medical treatments. Complementary treatments are not meant to substitute for traditional medical care. Be sure to notify your doctor if you are consuming nutritional supplements or homeopathic (nonprescription) remedies as they may interact with the prescribed medical therapy.

    Complementary treatments may include:

    • Massage therapy
    • Nutritional dietary supplements, herbal remedies, tea beverages, and similar products
    • Yoga

    What are the potential complications of motor neuron diseases?

    Some types of motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease) are fatal due to respiratory failure. Other MNDs progress slowly and are not fatal, but can seriously affect the quality of your life and lead to other serious complications. You may be able to minimize your risk of some complications, delay progression of the disease, and improve your quality of life by following the treatment plan you and your healthcare professional design specifically for you. Complications of MNDs can include:

    • Adverse effects of MND treatments
    • Aspiration/choking
    • Inability to perform daily tasks and disability
    • Paralysis
    • Pulmonary aspiration (inhaling substances into lungs)
    • Respiratory arrest
    • Weight loss
    • Withdrawal or depression
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      Medical Reviewer: William C. Lloyd III, MD, FACS
      Last Review Date: 2020 Nov 30
      View All Brain and Nerves Articles
      THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
      1. Motor Neuron Diseases Fact Sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/motor_neuron_diseases/detail_motor_neuron_diseases.htm.
      2. National Amyotrophic Lateral Sclerosis (ALS) Registry Frequently Asked Questions. Centers for Disease Control and Prevention. https://wwwn.cdc.gov/ALS/ALSFAQ.aspx#k
      3. NINDS Primary Lateral Sclerosis Information Page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/primary_lateral_sclerosis/primary_lateral_sclerosis.htm
      4. SOD1. Genetics Home Reference. http://ghr.nlm.nih.gov/gene/SOD1
      5. Rowland LP. Progressive muscular atrophy and other lower motor neuron syndromes of adults. Muscle Nerve 2010; 41:161.