Amyotrophic lateral sclerosis (a-my-o-TROE-fik LAT-ur-ul skluh-ROE-sis), known as ALS, is a nervous system disease that affects nerve cells in the brain and spinal cord. ALS causes loss of muscle control. The disease gets worse over time.

ALS is often called Lou Gehrig's disease after the baseball player who was diagnosed with it. The exact cause of the disease is still not known. A small number of cases are inherited.

ALS often begins with muscle twitching and weakness in an arm or leg, trouble swallowing or slurred speech. Eventually ALS affects control of the muscles needed to move, speak, eat and breathe. There is no cure for this fatal disease.


Symptoms of ALS vary from person to person. Symptoms depend on which nerve cells are affected. ALS generally begins with muscle weakness that spreads and gets worse over time. Symptoms might include:

  • Trouble walking or doing usual daily activities.
  • Tripping and falling.
  • Weakness in the legs, feet or ankles.
  • Hand weakness or clumsiness.
  • Slurred speech or trouble swallowing.
  • Weakness associated with muscle cramps and twitching in the arms, shoulders and tongue.
  • Untimely crying, laughing or yawning.
  • Thinking or behavioral changes.

ALS often starts in the hands, feet, arms or legs. Then it spreads to other parts of the body. Muscles get weaker as more nerve cells die. This eventually affects chewing, swallowing, speaking and breathing.

There's generally no pain in the early stages of ALS. Pain also is not common in the later stages. ALS doesn't usually affect bladder control. It also usually doesn't affect the senses, including the ability to taste, smell, touch and hear.


ALS affects the nerve cells that control voluntary muscle movements such as walking and talking. These nerve cells are called motor neurons. There are two groups of motor neurons. The first group extends from the brain to the spinal cord to muscles throughout the body. They're referred to as upper motor neurons. The second group extends from the spinal cord to muscles throughout the body. They're referred to as lower motor neurons.

ALS causes both groups of motor neurons to gradually deteriorate and then die. When motor neurons are damaged, they stop sending messages to the muscles. As a result, the muscles can't function.

For about 10% of people with ALS, a genetic cause can be identified. For the rest, the cause is not known.

Researchers continue to study possible causes of ALS. Most theories center on a complex interaction between genes and factors in the environment.

Risk factors

Established risk factors for ALS include:

  • Genetics. For about 10% of people with ALS, a risk gene was passed down from a family member. This is called hereditary ALS. In most people with hereditary ALS, their children have a 50% chance of inheriting the gene.
  • Age. Risk increases with age up to age 75. ALS is most common between the ages of 60 and the mid-80s.
  • Sex. Before the age of 65, slightly more men than women develop ALS. This sex difference disappears after age 70.

Environmental factors, such as the following, have been associated with an increased risk of ALS.

  • Smoking. Evidence supports that smoking is an environmental risk factor for ALS. Women who smoke seem to be at even higher risk, particularly after menopause.
  • Environmental toxin exposure. Some evidence suggests that exposure to lead or other substances in the workplace or at home might be linked to ALS. Much study has been done, but no one agent or chemical has been consistently associated with ALS.
  • Military service. Studies indicate that people who have served in the military are at higher risk of ALS. It's not clear what about military service might trigger ALS. It might include exposure to certain metals or chemicals, traumatic injuries, viral infections, or intense exertion.


As the disease progresses, ALS causes complications, such as:

Breathing problems

Over time, ALS leads to weakness of the muscles used to breathe. People with ALS might need a device such as a mask ventilator to help them breathe at night. The device is similar to what someone with sleep apnea might wear. This type of device supports the person's breathing through a mask worn over the nose, the mouth or both.

Some people with advanced ALS choose to have a tracheostomy. This is a surgically created hole at the front of the neck leading to the windpipe. A ventilator may work better on a tracheostomy than on a mask.

The most common cause of death for people with ALS is breathing failure. Half of people with ALS die within 14 to 18 months of diagnosis. However, some people with ALS live 10 years or longer.

Speaking problems

Most people with ALS develop weakness of the muscles used to form speech. This usually starts with slower speech and occasional slurring of words. It then becomes harder to speak clearly. This can progress to the point that others can't understand the person's speech. Other forms of communication and technology are used to communicate.

Eating problems

People with ALS can develop weakness of the muscles involved with swallowing. This can lead to malnutrition and dehydration. They are also at higher risk of getting food, liquids or saliva into the lungs, which can cause pneumonia. A feeding tube can reduce these risks and ensure proper hydration and nutrition.


Some people with ALS have problems with language and decision-making. Some are eventually diagnosed with a form of dementia called frontotemporal dementia.