A health condition that negatively affects motor neurons that are involved in muscle movements is called motor neuron disease (MND). Most of the time, MND affects the muscles that you do not even think about, including those that are involved in breathing, swallowing, chewing, talking, and walking. Unfortunately, it is not possible to cure this condition, and it usually worsens over time.
Furthermore, MND belongs to a group of health conditions called neurological disorders. These health conditions cause gradual damage to the motor neurons. In normal circumstances, the motor neurons in the brain (upper motor neurons) send messages to the motor neurons in the spinal cord (lower motor neurons). Thus, they move the muscles throughout the body.
Over time, this condition causes damage to these neurons, which may lead to muscle atrophy (weakness of the muscles), muscle stiffness, and overactive reflexes (also known as hyperreflexia). As a result, it may lead to disability and even death.
Types of Motor Neuron Disease
Physicians have divided this disorder into several types based on which part of the body is affected. For example:
Amyotrophic Lateral Sclerosis (ALS)
This is one of the most common types of MND, and it often impacts both upper and lower motor neurons. Sometimes, it is also called Lou Gehrig’s disease. In most cases, people who develop ALS may notice a quick loss of muscle control and paralysis.
Progressive Bulbar Palsy (PBP)
This type of motor neuron disease impacts the lower motor neurons that are connected to the brainstem (bulbar area). This region controls the muscles involved in speaking, chewing, swallowing, and other body functions. In some cases, this disorder is called progressive bulbar atrophy.
Primary Lateral Sclerosis (PLS)
In such cases, the condition affects the upper motor neurons only. Mostly, PLS first affects the legs and then the arms, hands, and torso. Sometimes, it may also affect the ability to chew, speak, and swallow.
Progressive Muscular Atrophy (PMA)
This form of MND affects the lower motor neurons only in males. Females may also develop PMA, but it is less common. In most cases, the symptoms appear at a younger age, including weakness in the hands, breathing problems, and others. Furthermore, PMA may spread to the lower part of the body over time, especially without treatment.
Spinal Muscular Atrophy (SMA)
This is an inherited disorder that negatively affects the lower motor neurons. Furthermore, it is one of the most common causes of death in infants. It develops due to a mutation (change) in the SMN1 gene, which causes a loss of SMN protein. As a result, it gradually destroys the lower motor neurons, which often cause muscle wasting and weakness.
Kennedy’s Disease
This is also a genetic form of MND, and it happens due to changes in the gene for the androgen receptor. It also worsens over time and may cause weakness in the arms, legs, shoulders, and pelvic area. People who develop it may experience the following symptoms. For example, numbness in the hands and feet, pain, and progressive muscle weakness.
Post-polio Syndrome (PPS)
This form of MND occurs in polio survivors, and it may cause serious damage to the motor neurons. Sometimes, PPS occurs decades after they have recovered from the original disorder. The most common symptoms include muscle twitches and atrophy, intolerance to cold, extreme tiredness (fatigue), pain, and joint weakness.
What Are The Symptoms of Motor Neuron Disease?
Usually, most people with motor neuron disease experience mild symptoms because this condition worsens gradually over time. Check some early symptoms below:
- Weakness in the ankles and legs
- Dysarthria (slurred speech)
- Muscle cramps and twitches
- Swallowing problems (dysphagia)
- Weight loss
- Pseudobulbar affect (difficulty stopping yourself from laughing or crying in inappropriate situations)
When the condition advances, it may also cause the following symptoms. These include:
- Sleep disturbances (insomnia)
- Difficulty breathing when lying down
- Recurrent chest infections
- Confusion
- Headaches that often occur in the morning
- Extreme tiredness (fatigue)
- Difficulty concentrating
- Memory loss
Immediately contact your healthcare professional if any of the previous symptoms occur. Otherwise, it may lead to permanent damage.
Causes and Risk Factors
These disorders appear due to problems with the motor neurons. In people with MND, the neurons slowly stop functioning. Nowadays, experts do not fully understand what exactly causes it. However, some types of NMD are inherited. It means they run in families. Check some ways on how people inherit the abnormal genes that cause NMD:
- Autosomal recessive – In this case, the baby inherits one copy of the mutated gene from each biological parent.
- Autosomal dominant – It means you will get only one abnormal gene from one biological parent, and it is not necessary that you will develop MND.
- X-linked inheritance – In such cases, MND happens when the mother carries the abnormal gene on one X chromosome and passes the condition to the male children.
Physicians have identified some factors that could elevate your risk of developing non-inherited MND. For example:
- Viral infections
- Environmental factors (such as prolonged exposure to chemicals or toxins)
- Genetic factors
- Age – This condition is more common among older adults (between the ages of 60 and 70), but it may also affect younger adults and children.
- A family history – People who have a parent or sibling with motor neuron disease or frontotemporal dementia are at higher risk of developing it.
Diagnosis
Commonly, it is difficult to diagnose this disorder, especially in the early stages, because there are no tests that can confirm MND. However, when physicians suspect this disorder may ask some questions and perform the following tests and procedures. Check some examples below:
- Electromyography (EMG) – This is a specific test used to measure the electrical activity in the muscles. Usually, EMG is used to check for problems with muscles, nerves, or the neuromuscular junction.
- Nerve conduction study – It is used to measure the speed of the impulses that nerves send to each other.
- MRI (magnetic resonance imaging) scan – This is an imaging test used to get detailed images of different structures and organs in the body (including the brain and spinal cord).
Your doctor may also perform additional tests to exclude other health conditions that cause similar symptoms. For example, spinal tap (lumbar puncture), genetic tests, urine tests, blood tests, and others.
Treatment
Unfortunately, there is no way to cure MND. That’s why the treatment focuses on reducing the symptoms, preventing life-threatening complications, and improving your quality of life. In most cases, people with MND need physical therapy that helps maintain muscle strength and joint flexibility. If you have dysphagia, your doctor may recommend a gastrostomy tube that is inserted through the abdominal wall into the stomach. They may also recommend the following medicines to ease the symptoms. For example:
- Baclofen – This medicine is used to reduce muscle spasms.
- Phenytoin or Quinine (to reduce muscle cramps)
- Antidepressants
- Benzodiazepines to relieve pain
- Glycopyrrolate (it helps decrease drooling)
- Riluzole and Edaravone – These medications are often recommended for people with ALS to improve their symptoms and lifespan.
Frequently Asked Questions
When should I see my healthcare provider?
Usually, it is recommended to visit a doctor if you notice symptoms that resemble MND (such as muscle weakness). You should also inform your doctor if the treatment you are taking is not working.
What is the life expectancy of a person with motor neuron disease?
Typically, the life expectancy fluctuates among people with this disorder. The 2 to 5-year survival rate is about 10% once a person is diagnosed with MND.
What is the main cause of motor neuron disease?
Experts do not fully understand what exactly causes MND, but they think it results from a combination of genetic and environmental factors. Furthermore, approximately 90% to 95% of diagnosed cases are sporadic (non-inherited). If you have any other questions, ask your healthcare provider.
