MS vs. ALS: how do they differ?
Fact-checked by Although multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS) are both neurodegenerative diseases that share some symptoms, there are key differences between them in terms of progression, treatment, and outlook.
In MS, the patient’s own immune system mistakenly attacks healthy parts of the nervous system. These inflammatory attacks target the protective covering around nerve cells, known as the myelin sheath, disrupting nerve signaling and ultimately leading to nerve cell death.
ALS, also known as Lou Gehrig’s disease, affects the nerve cells that control muscles, called motor neurons. The progressive damage and death of motor neurons impairs the function of muscles, which weaken and deteriorate over time.
Understanding MS versus ALS can help patients and caregivers know what to expect for their specific diagnosis.
Overlapping symptoms: How MS and ALS are alike
Both MS and ALS are central nervous system disorders, meaning they affect the brain and spinal cord. They both cause neurodegeneration, or progressive nerve cell dysfunction and death, and lead to movement and mobility problems.Â
Overlapping MS and ALS symptoms may include:
- muscle stiffness and spasms
- muscle weakness
- fatigue
- loss of coordination
- difficulty walking
- slurred speech
These similarities are particularly prominent in early disease stages, at which point it may be challenging to tell MS and ALS apart. While muscle weakness in MS and ALS may at first manifest in similar ways, it becomes easier to distinguish the diseases as other symptoms develop. These early symptoms also overlap with those of other neurodegenerative diseases.
There is no single test to confirm either MS or ALS, so reaching a diagnosis can take time. Doctors will consider a patient’s medical history and perform several diagnostic tests to differentiate between the diseases and rule out other possible causes of symptoms.
ALS and MS are also similar in that their exact causes are unknown, and neither currently has a cure.
Differences between MS and ALS
While they have some overlap, there are a number of key MS and ALS differences that are important to be aware of.
Cause
In most cases, both ALS and MS are thought to arise from a combination of environmental and genetic risk factors.
MS is not a genetic disease and is not typically inherited in families. Still, having a first-degree relative with MS increases a person’s risk, which may be related to the inheritance of genetic risk factors that affect immune function.
ALS can be inherited or sporadic. About 10% of ALS cases are caused by genetic mutations that run in families (familial ALS). The remaining majority of cases are not inherited (sporadic ALS), but scientists believe that genetic factors may still play an important role for these patients.
Patterns and mechanisms of nerve damage
With MS, the immune system attacks myelin. This myelin loss, or demyelination, leaves nerve cells vulnerable to damage, and they eventually die off. In ALS, motor neurons first become damaged, losing myelin as they become sicker and start to die.
Essentially, MS demyelination drives neurodegeneration, while ALS demyelination is a secondary consequence of neurodegeneration. The body’s attempt to repair nervous system damage leads to sclerosis, or scarring, in both cases.
The two diseases also differ in the nerves they affect. While motor neurons are the main target of ALS, MS-related damage can happen throughout the brain and spinal cord.
Comparing sclerosis patterns can help identify the diseases, and finding damaged areas using MRI scans is vital for an MS diagnosis.
How each disease progresses
The typical disease courses of MS and ALS differ substantially. ALS is characterized by a rapid and progressive decline over time, with motor neurons steadily dying off. On the other hand, the course of MS is more variable and cannot always be predicted at the time of diagnosis.
Initially, MS most often takes a relapsing-remitting course, characterized by periods of new or worsening symptoms (relapses) interspersed with periods where symptoms disappear or ease substantially. Some people with MS eventually develop or start off with progressive disease, where symptoms steadily worsen over time, but this progression is usually much slower than what’s seen with ALS.
| Disease features | MS | ALS |
|---|---|---|
| Cause | Immune attacks on myelin | Loss of motor neurons |
| Typical age of onset | 20 to 50 years | 55 to 75 years |
| Progression | Varies, may have a progressive or relapsing-remitting course | Rapid and continuous progression |
| Life expectancy | Normal or near-normal | Three to five years after symptom onset |
Late-stage symptoms and long-term outlook
As the two diseases progress, they become increasingly distinct. Because a wide range of nerve cells can be affected, other MS symptoms that may emerge include pain and abnormal sensations, vision problems, issues with bladder and bowel control, emotional difficulties, and cognitive dysfunction.
Although mobility can become increasingly affected in MS, only a minority of patients will develop severe disabilities, particularly with modern treatments. Around one-third of patients will need a wheelchair or mobility aid after 20 years.
In contrast, paralysis and total loss of functional independence are typical features of late-stage ALS. People with ALS continue to lose physical control until they can no longer speak, swallow, or breathe on their own. Some patients may develop locked-in syndrome, where their mind is fully intact, but they have lost all voluntary muscle control.
Life expectancy
Although MS prognosis varies, most people with the disease have a normal or near-normal life expectancy. By contrast, ALS life expectancy is considerably shortened. The average survival time after a diagnosis for people with ALS is about three to five years, although as many as 10% may live 10 years or longer.
Prevalence
MS is more common than ALS. While ALS meets the criteria to be considered a rare disease in the U.S. and Europe, MS does not.
According to data from the National ALS Registry, there were around 34,000 people living with ALS in the U.S. in 2025, corresponding to a prevalence of about 10.1 cases for every 100,000 people. With current data, it is estimated that nearly 1 million people in the U.S., and about 2.9 million worldwide, have MS.
The prevalence of both diseases appears to be increasing over time.
MS in women is two to three times more common than MS in men, while men are at a slightly higher risk of developing ALS than women. Scientists don’t entirely understand why.
The most common age of MS diagnosis is 20 to 50, while ALS is typically diagnosed later, between the ages of 55 and 75.
Treatments
There is currently no cure for ALS or MS. Treatments involve medications to slow disease progression, ease symptoms, and improve life quality. The main difference in ALS versus MS treatment is that ALS therapies focus on protecting motor neurons, while most MS therapies target the excessive immune activity that causes the disease.
MS medications fall into two major categories: disease-modifying therapies to slow or stop new disease activity or progression, and supportive therapies that help ease symptoms. Lifestyle changes, such as adjusting diet and increasing exercise, may also help manage symptoms.
Three treatments are currently approved for ALS — Radicava (edaravone), Tiglutik (riluzole), and Qalsody (tofersen) —  which are intended to slow disease progression. Medications for symptom management and other non-drug therapies may help control symptoms and improve overall quality of life.
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