ALS is a disease that kills nerve cells controlling your muscles

ALS (amyotrophic lateral sclerosis) is a progressive neurological disease in which nerve cells in the brain and spinal cord gradually die. These nerve cells, called motor neurons, send signals that tell your muscles to contract and move. When motor neurons die, the muscles they control weaken, waste away, and eventually stop working. Over time, this affects your ability to walk, speak, swallow, and breathe.

The disease is always fatal. Most people with ALS die from respiratory failure—the muscles that control breathing stop working—typically two to five years after symptoms begin. Some people live longer, and a small number live ten years or more. There is no cure, though some treatments can slow progression or ease symptoms.

ALS is rare. In the United States, roughly 5,000 people are diagnosed each year, and about 16,000 people are living with the disease at any given time. It most often appears in people aged 40 to 70, though it can strike younger adults and occasionally children.

Key Takeaways

  • ALS kills motor neurons in the brain and spinal cord, causing muscles to weaken and waste away over months or years.
  • The disease affects voluntary muscles—those you control consciously—but not heart muscle or the smooth muscles in your digestive system.
  • Symptoms usually start in one part of the body (the hands, feet, or speech) and spread to other areas as the disease progresses.
  • Most people with ALS die from respiratory failure when the diaphragm and intercostal muscles stop working, typically within two to five years of diagnosis.
  • There is no cure, but medications like riluzole and edaravone can slow progression, and other treatments manage symptoms and maintain quality of life.

How ALS damages motor neurons

Motor neurons are nerve cells that carry electrical signals from your brain and spinal cord to your muscles. When you decide to move your arm, your brain sends a signal down a motor neuron to the muscle fibers in your arm, telling them to contract. In ALS, these motor neurons gradually break down and die. Scientists do not fully understand why this happens, but the damage involves a buildup of abnormal proteins, problems with how cells handle calcium and other chemicals, and inflammation in the nervous system.

There are two types of motor neurons: upper motor neurons (in the brain) and lower motor neurons (in the spinal cord and brainstem). Both types die in ALS, though the rate and pattern vary between people. As neurons die, the muscles they controlled no longer receive signals and begin to atrophy—they shrink and weaken. Eventually, those muscles stop working entirely.

ALS affects only voluntary muscles—the ones you control consciously, like those in your arms, legs, face, and chest. It does not damage your heart muscle or the smooth muscles in your stomach and intestines, which is why your heart keeps beating and your digestive system continues to work even as the disease progresses.

The two main patterns of ALS onset

Limb-onset ALS begins in the arms or legs and accounts for about 60 to 70 percent of cases. A person might notice weakness or clumsiness in one hand, difficulty walking, or tripping over their own feet. The weakness usually starts on one side of the body and spreads to the other side over weeks or months. Muscle cramps, twitching (called fasciculations), and loss of muscle bulk often appear before weakness becomes obvious.

Bulbar-onset ALS begins in the muscles that control speech and swallowing and accounts for about 25 to 30 percent of cases. A person might notice their speech becoming slurred or nasal, difficulty swallowing, or choking on food or liquids. Some people experience jaw weakness or difficulty chewing. Bulbar-onset ALS tends to progress more rapidly than limb-onset, though individual cases vary widely.

Regardless of where ALS starts, it eventually spreads to other parts of the body. A person with limb-onset may develop speech and swallowing problems months or years later. Someone with bulbar-onset will eventually develop weakness in the arms and legs. As the disease advances, respiratory muscles weaken, making breathing harder and eventually requiring mechanical support.

Why ALS is progressive and what "progressive" means

ALS is progressive, meaning it gets worse over time. The rate of progression varies significantly between people. Some people experience rapid decline, with major changes in function over weeks. Others decline slowly, with noticeable changes spread over months or years. There is no way to predict at diagnosis how fast a particular person's disease will advance.

Early in the disease, a person might notice weakness in one limb or slight speech changes but remain largely independent. As months pass, weakness spreads to other limbs, speech becomes harder to understand, and swallowing becomes difficult. In later stages, a person may lose the ability to walk, feed themselves, or speak clearly. Eventually, respiratory muscles fail, and without mechanical ventilation, breathing stops.

The progression is relentless—there are no remissions or periods where the disease stops advancing. Some treatments can slow the rate of decline, but none can stop it or reverse damage that has already occurred. This is why early diagnosis and starting treatment quickly matter: slowing the disease even slightly can preserve function and independence for longer.

Inherited versus sporadic ALS

About 90 percent of ALS cases are sporadic, meaning they occur randomly in people with no family history of the disease. Scientists have identified environmental and genetic risk factors that may contribute—smoking, military service, exposure to certain chemicals, and carrying certain genetic variations—but most sporadic cases do not have a clear single cause.

About 10 percent of cases are familial ALS (fALS), meaning the disease runs in families. People with a parent, sibling, or child with ALS have a higher risk of developing it themselves. Familial ALS is caused by mutations in specific genes. The most common is the C9orf72 gene, followed by SOD1 and FUS. Genetic testing can identify these mutations, which is useful for family members who want to know their risk and for researchers studying how these genes contribute to the disease.

Whether ALS is inherited or sporadic, the disease itself works the same way: motor neurons die, muscles weaken, and the disease progresses. The genetic information matters mainly for understanding risk in family members and for developing targeted treatments based on the specific genetic cause.

Symptoms beyond muscle weakness

While muscle weakness and wasting are the hallmark of ALS, other symptoms often develop as the disease advances. Muscle cramps and twitching (fasciculations) are common early signs. Pain can occur as muscles weaken and atrophy, or from the effort of moving weakened limbs. Fatigue is nearly universal and often worsens as the disease progresses and breathing becomes harder.

Speech and swallowing problems emerge as the muscles controlling the mouth, throat, and tongue weaken. A person may speak unclearly, have difficulty chewing, or cough when drinking liquids. Constipation and urinary problems can develop because the smooth muscles controlling these functions are affected indirectly by overall weakness and reduced mobility. Cognitive changes—difficulty concentrating, memory problems, or mood changes—occur in a minority of people, usually late in the disease.

Importantly, sensation (the ability to feel touch, temperature, and pain) remains normal in ALS. A person with advanced ALS who cannot move can still feel and think clearly. This is why communication devices and palliative care become so important—people with severe physical paralysis retain full mental awareness and the ability to experience quality of life.

How ALS is diagnosed

There is no single test that diagnoses ALS. Instead, doctors use a combination of clinical examination, electromyography (EMG), and imaging to rule out other diseases and confirm motor neuron damage. An EMG measures electrical activity in muscles and can show the pattern of motor neuron loss typical of ALS. MRI of the brain and spinal cord rules out other conditions like tumors or spinal cord compression that could cause similar symptoms.

Blood tests may include genetic testing if familial ALS is suspected, or tests to rule out other diseases. A neurologist will examine muscle strength, reflexes, and signs of muscle wasting and twitching. The diagnosis is based on evidence of motor neuron degeneration in multiple body regions and the progressive nature of symptoms over time.

Diagnosis typically takes weeks to months because doctors must rule out other treatable conditions first. Early diagnosis matters because starting treatment sooner may slow progression more effectively, but it is important that the diagnosis is correct before beginning long-term treatment.

Frequently Asked Questions

Is ALS the same as Lou Gehrig's disease?

Yes. Lou Gehrig's disease is another name for ALS. The baseball player Lou Gehrig was diagnosed with the disease in 1939, and it became widely known by his name. ALS, amyotrophic lateral sclerosis, and Lou Gehrig's disease all refer to the same condition.

Can you have ALS and not know it?

ALS always causes noticeable symptoms—weakness, speech changes, or difficulty swallowing. You cannot have ALS without experiencing these changes. However, early symptoms can be subtle or mistaken for other conditions, so diagnosis may be delayed. If you notice new weakness or speech changes, seeing a neurologist is important.

Does ALS affect your mind or memory?

In most people, ALS does not affect thinking or memory. The disease damages motor neurons but leaves cognitive function intact. A small percentage of people develop cognitive or behavioral changes, usually late in the disease. This is why communication devices are so important—people with severe physical paralysis retain full mental awareness.

Can children get ALS?

ALS is extremely rare in children. The disease typically appears in adults over 40. When ALS does occur in younger people or children, it is usually familial (inherited) and caused by a specific genetic mutation. Juvenile-onset ALS tends to progress more slowly than adult-onset disease.

What is the difference between ALS and MS?

ALS and multiple sclerosis (MS) are different diseases affecting different parts of the nervous system. MS damages the insulation around nerve fibers, causing symptoms that come and go. ALS kills motor neurons themselves, causing progressive weakness without remission. MS is not fatal; ALS is. The treatments and prognosis are completely different.