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Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig's Disease)

What is Amyotrophic Lateral Sclerosis (ALS)?

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Amyotrophic lateral sclerosis (ALS) is a progressive disorder of the part of the nervous system that controls voluntary movements. It is sometimes called Lou Gehrig's disease for the famous baseball player who died of the disease. The muscles become progressively weaker, and the condition eventually leads to paralysis and death.

ALS is one of a group of diseases known as motor neuron diseases. Neurons are nerve cells, and motor neurons are neurons that control movement.

  • Movement occurs when neurons in the brain (upper motor neurons) send messages to neurons in the spinal cord (lower motor neurons). The lower motor neurons relay these messages via nerves to the specific muscles that carry out the movement.
  • In some motor neuron diseases, only the upper motor neurons are affected, or only the lower motor neurons. In ALS, however, both upper and lower motor neurons are affected.
  • The neurons die and stop sending messages to muscles. The muscles are unable to function without these messages and gradually become weaker. They waste away (atrophy) and twitch (fasciculate).
  • Eventually all voluntary movement is lost, and muscles become paralyzed.

The loss of strength and control follows different patterns in different people.

  • Some people lose control of one or both legs first. They may have trouble walking or running or become clumsy, tripping, or falling.
  • Others notice a problem with a hand or arm first, having problems with simple tasks such as writing or buttoning a shirt.
  • In some, speech or swallowing is the first thing affected.
  • In every case, the weakness and disability spread to almost every part of the body.
  • The diaphragm is a muscle under the lungs that partly controls their expansion as they take in air. When the chest muscles and diaphragm become too weak, the person is no longer able to breathe on his own. This is called respiratory failure and is by far the leading cause of death for people with ALS.
  • Most people with ALS die within five years of the onset of symptoms.

In most cases, ALS does not affect a person's mental abilities, senses, reasoning, memory, or personality. Senses such as vision and touch are not lost. Most people retain their ability to move their eyes. Bowel and bladder control are not impaired.

ALS affects all races and ethnic groups. The disease can occur at any age but is most common in people aged 40-60 years. Men are affected more often than women.

No cure is available for ALS. The effects of the disease are not reversible. Research is focused on finding the cause of the neuron degeneration and stopping it.

What causes amyotrophic lateral sclerosis (ALS)?

We do not know exactly what causes ALS. Although some cases of ALS are hereditary (run in families), most are not. A mutation of a gene called SOD1 has been identified in some of the hereditary cases, but we do not know what role the mutation plays in the disease.

Using an evidence-based approach, smoking was found to be more likely than not a risk factor for ALS based on two excellent studies by Kamel et al. and Nelson et al. Smoking has a broad public health impact, no redeeming features, and is a modifiable risk factor. Evidence also supported the conclusion that the following were probably not risk factors for ALS:

  • trauma,
  • physical activity,
  • residence in rural areas, and
  • alcohol consumption.
Medically Reviewed by a Doctor on 6/16/2016
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Amyotrophic Lateral Sclerosis (ALS) Definition

A classic motor neuron disease. Motor neuron diseases are progressive chronic diseases of the nerves that come from the spinal cord responsible for supplying electrical stimulation to the muscles. This stimulation is necessary for the movement of body parts.


Read What Your Physician is Reading on Medscape

Amyotrophic Lateral Sclerosis »

Amyotrophic lateral sclerosis (ALS) is a disease of unknown cause characterized by slowly progressive degeneration of upper motor neurons (UMNs) and lower motor neurons (LMNs).

Read More on Medscape Reference »

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