About motor neuron disease

What is motor neuron disease?

Motor neuron disease comprises a group of severe disorders of the nervous system characterized by progressive degeneration of motor neurons (neurons are the basic nerve cells that combine to form nerves). Motor neurons control the behavior of muscles. Motor neuron diseases may affect the upper motor neurons, nerves that lead from the brain to the medulla (a part of the brain stem) or to the spinal cord, or the lower motor neurons, nerves that lead from the spinal cord to the muscles of the body, or both. Spasms and exaggerated reflexes indicate damage to the upper motor neurons. A progressive wasting (atrophy) and weakness of muscles that have lost their nerve supply indicate damage to the lower motor neurons.

What are the symptoms for motor neuron disease?

Amyotrophic Lateral Sclerosis (ALS)

ALS affects both your upper and lower motor neurons. With ALS, you gradually lose control over the muscles that help you walk, talk, chew, swallow, and breathe. Over time, they weaken and waste away. You may also have stiffness and twitches in your muscles.

Primary Lateral Sclerosis (PLS)

PLS is similar to ALS, but it affects only upper motor neurons.

It causes Weakness and stiffness in the arms and legs, a slowed walk, and poor coordination and balance. Speech also becomes slow and slurred.

Progressive Bulbar Palsy (PBP)

This is a form of ALS. Many people with this condition will eventually develop ALS.

The stem has motor neurons that help you chew, swallow, and speak. With PBP, you might slur your words and have trouble chewing and swallowing. It also makes it hard to control emotions. You may laugh or cry without meaning to.

Pseudobulbar Palsy

This is similar to progressive bulbar palsy. It affects motor neurons that control the ability to talk, chew, and swallow. Pseudobulbar palsy causes people to laugh or cry with no control.

Progressive Muscular Atrophy

This form is much less common than ALS or PBP. Weakness usually starts in your hands and then spreads to other parts of the body. Your muscles get weak and may cramp. This disease can turn into ALS.

Spinal Muscular Atrophy

This causes Weakness in the upper legs and arms, and in the trunk.

SMA comes in different types that are based on when symptoms first appear:

Type 1 (also called Werdnig-Hoffmann disease). Children with this type can't sit on their own or hold up their head. They have weak muscle tone, poor reflexes, and trouble swallowing and breathing.

Type 2. Kids with this form can sit, but they can't stand or walk alone. They may also have trouble breathing.

Type 3 (also called Kugelberg-Welander disease). It affects how a child can walk, run, stand up, and climb stairs. Kids with this type may also have a curved spine or shortened muscles or tendons around their joints.

Kennedy's Disease

Males with Kennedy's disease have shaking hands, muscle cramps and twitches, and Weakness in their face, arms, and legs. They may have trouble swallowing and speaking. Men can have enlarged breasts and a low sperm count.

What are the causes for motor neuron disease?

Amyotrophic Lateral Sclerosis (ALS)

Most of the time, ALS is what doctors call “sporadic.” This means anyone can get it. Only about 5% to 10% of cases in the United States run in families.

Primary Lateral Sclerosis (PLS)

Like ALS, it usually starts in people 40 to 60 years old. The muscles get stiffer and weaker over time. But unlike ALS, people don't die from it.

Progressive Muscular Atrophy

This form is much less common than ALS or PBP. It can be inherited or sporadic.

Spinal Muscular Atrophy

This is an inherited condition that affects lower motor neurons. A defect in a gene called SMN1 causes spinal muscular atrophy. This gene makes a protein that protects your motor neurons. Without it, they die.

Kennedy's Disease

It’s also inherited, and it affects only males. Females can be carriers but don’t get ill from it. A woman with the Kennedy’s disease gene has a 50% chance of passing it on to a son.

What are the risk factors for motor neuron disease?

Amyotrophic Lateral Sclerosis (ALS)

ALS usually starts between the ages of 40 and 60.  Most people with the disease live for 3 to 5 years after their symptoms start, yet some people can live for 10 years or longer.

Primary Lateral Sclerosis (PLS)

Like ALS, it usually starts in people 40 to 60 years old. The muscles get stiffer and weaker over time. But unlike ALS, people don't die from it.

Spinal Muscular Atrophy

This causes weakness in the upper legs and arms, and in the trunk.

SMA comes in different types that are based on when symptoms first appear:

Type 1 (also called Werdnig-Hoffmann disease). It starts around age 6 months. 

Type 2. It starts between 6 and 12 months. 

Type 3 (also called Kugelberg-Welander disease). It starts between ages 2 and 17. 

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