What is amyotrophic lateral sclerosis (ALS)?
Amyotrophic lateral sclerosis (ALS), often known as Lou Gehrig’s disease or maladie de Charcot in French, is the most common form of motor neuron disease (MND).
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease or Charcot’s disease, is the most common form of motor neuron disease (MND).
Definition of amyotrophic lateral sclerosis (SLA)
Amyotrophic lateral sclerosis is the most common form of motor neuron disease. It is sometimes called Charcot’s disease in Europe or Lou Gehrig’s disease in North America.
This rare neurodegenerative condition is characterized by the progressive deterioration of nerve cells (motor neurons) that initiate and control muscle movement. As these cells die, the muscles they stimulate deteriorate, weaken, and eventually lose normal function.
ALS is not contagious. There is no cure for ALS and few treatment options for the majority of people living with the disease.
How ALS affects the body
Voluntary muscles
ALS destroys the motor neurons (nerve cells) in the body, leading to atrophy of the voluntary muscles (which deteriorate and weaken). Voluntary muscles are those that a person can control consciously.
These include the muscles in the arms (biceps, triceps) and legs (quadriceps, calves). The muscles of the face, neck, and tongue are also voluntary muscles, allowing us to eat, support and move the head, and make facial expressions.
In summary:
- The motor neurons that control voluntary muscles die.
- As a result, these voluntary muscles no longer receive signals and become weak and atrophied.
- Muscle spasms or twitches (fasciculations) may also occur.
Involuntary muscles
Involuntary muscles are not under a person’s conscious control. They function automatically, without the need to think about them. These include the heart muscle and the smooth muscles of internal organs.
Unlike voluntary muscles, they do not rely on the motor neurons affected by ALS and are therefore generally spared. However, some respiratory or digestive symptoms may appear later due to weakness in the voluntary muscles involved in breathing or swallowing.
Senses and functions typically spared
ALS usually does not affect the five senses (sight, hearing, taste, smell, touch) or the heart. Some studies show that certain individuals may experience a reduced sense of smell.
ALS primarily affects the muscles that we control voluntarily (such as moving an arm, speaking, or swallowing), but it does not directly impact involuntary muscles (such as the heart or digestive muscles), which continue to function normally for most of the disease.
The biology of amyotrophic lateral sclerosis (ALS)
In ALS/MND, motor neurons begin to die. As this happens, the brain can no longer send messages to voluntary muscles to tell them to move. In other words, the muscles begin to atrophy. Over time, ALS spreads throughout the body, weakening all voluntary muscles, including those needed for breathing, which can lead to respiratory problems.
Two main types of motor neurons:
- Upper motor neurons: Located in the brain, they tell the lower motor neurons when and how the muscles should move.
- Lower motor neurons: Located in the spinal cord, they send signals directly to the muscles to make them move, following instructions from the upper motor neurons.
Life expectancy and progression of ALS
ALS reduces life expectancy. Some treatments are available, but there is currently no cure. As a result, about 80% of people with the disease live 2 to 5 years after diagnosis.
The rate at which a person loses muscle function can vary widely. For some, deterioration happens quickly, while for others, the decline is much slower and occurs over many years.
Learn about ALS symptoms and early warning signs
ALS affects each person differently. Learn about the early signs that can help lead to a quicker diagnosis.