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ALS vs. MS: What’s the Difference Between These Two Brain Diseases?

ALS and MS have similar symptoms, which means research discoveries about one brain disease can help us understand the other—but there are also some notable differences.

Amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) are neurologic diseases that share some similar symptoms. Because of those similarities, the two diseases are often confused, so it’s also important to understand their key differences.

We know that all parts of the brain are connected. That means research discoveries in one disease area will benefit our understanding of other diseases as well. This interconnection fuels our Cure One, Cure Many approach and our commitment to funding research across the full spectrum of brain diseases and disorders. Taking a closer look at the similarities and differences between ALS and MS gives us a concrete way to understand the importance of research across related diseases.

What is MS?

Multiple sclerosis (MS) is a chronic disease of the central nervous system, which includes the brain, spinal cord, and optic nerves. It is believed to be an autoimmune disease in which the immune system attacks myelin (the protective coating that surrounds nerve cells) and causes damage to the nerve itself. MS affects more than 1 million people in the United States and 2.5 million worldwide, with 10,000 new cases diagnosed each year.

This unpredictable disease interrupts communication between the brain and the body, causing muscle weakness, fatigue, and balance problems. Symptoms usually begin between ages 20 to 40. MS often causes distinct attacks in which symptoms get worse and then subside. People with MS may experience times of relapse, when symptoms increase or new ones start, followed by periods of remission, when symptoms are more mild.

While the cause of MS is unknown, abnormalities of the immune system, as well as genetic and environmental factors, could contribute to the risk of developing the disease. Because the disease affects two to three times more women than men, there may be a hormonal component.

What is ALS?

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that attacks the nerve cells in the brain and spinal cord that control voluntary movement. As these nerve cells (called motor neurons) decline, they stop sending messages to the muscles, causing them to weaken, stiffen, twitch, and atrophy (lose muscle mass and deteriorate). About 30,000 people in the U.S. and more than 400,000 people globally live with ALS.

The rapidly progressing disease most commonly affects people between age 40 and 70 and has an average survival of three to five years. Early symptoms may affect one body part, but as the disease progresses, people with ALS often have trouble standing, walking, moving, swallowing, and speaking. ALS is ultimately fatal, typically due to respiratory failure when the muscles needed to breathe become too weak. 

While ALS symptoms are caused by a decline in motor neuron function, scientists are still learning why it occurs in some people and not others. In five to 10 percent of cases, the disease is inherited from a parent with the disease-causing gene. But in 90 to 95 percent of cases, the disease is sporadic, meaning it occurs without clear cause, risk factor, or family history. Men are slightly more likely to develop the disease than women, and some studies suggest military veterans are at greater risk. Ongoing research is looking at the impact of environmental, behavioral, and occupational factors.

Differences Between MS and ALS

While MS and ALS have similarities, the two brain diseases have some notable differences. Disease onset and progression is different. Symptoms of MS typically start between ages 20 and 40, while symptom onset for ALS is often later in life, between ages 40 and 70. While MS usually progresses in an unpredictable way with distinct attacks and periods of relapse and remission, ALS has a gradual onset and a rapid progressive decline.

The prognoses are also different. ALS is ultimately fatal, with an average survival of three to five years and only 10 percent of people living 10 or more years. On the other hand, people with MS usually live longer, between 25 and 35 years on average, while managing their symptoms with medication, therapies, and lifestyle changes.

While they seem similar, the diseases have different underlying mechanisms. In MS, the immune system is believed to attack nerve cells’ protective coating, damaging the nerves and disrupting communication between the brain and body. ALS causes motor neurons to decline and die, so they can no longer send messages to the muscles.

Similarities Between MS and ALS

The clearest similarity between MS and ALS is their common symptoms. Both diseases cause people to have difficulty moving due to muscle weakness, numbness, stiffness, or problems with balance and coordination. In both cases, the motor neurons, or nerve cells in the brain and spinal cord, are affected.

In addition, neuroinflammation across the central nervous system plays a role in both diseases. Neuroinflammation — swelling in the brain and spinal cord — is an immune response. It can be a natural, protective response to illness, injury, or infection, or in the case of MS, a faulty response that causes damage. Research shows that prolonged or excessive inflammation may be a key driver of the onset and progression of many neurologic diseases and disorders.

The Importance of Research

With these similarities in mind, more collaborative research could help us understand both ALS and MS. For example, the American Brain Foundation’s 2025 Cure One, Cure Many award supports a ground-breaking, cross-industry research initiative on neuroinflammation’s role in brain disease. Because neuroinflammation plays a role in nearly all brain diseases, including ALS and MS, understanding this aspect of the body’s inflammatory response will help develop innovative approaches that target multiple brain diseases.

We have already seen how exciting research discoveries and innovative studies have an incredible impact on brain disease treatments for both ALS and MS. But right now, these diseases do not have a cure. Research is the only way to better understand these diseases so we can find more effective ways to diagnose, treat, prevent, and ultimately cure them. When a breakthrough for one disease area leads to advancements in other diseases, we have the power to help even more people live a life without brain disease.

The American Brain Foundation was founded to bring researchers and donors together in the fight against brain disease. Learn more about brain disease or make a gift to support brain research.