The Differences Between MS and ALS

Both are neurological diseases, but there are some key distinctions

Man with Multiple Sclerosis in a motorized wheelchair in his yard
Mark Hunt/Getty

Multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease) are similar in some ways. For instance, both diseases involve the nerves and the word "sclerosis," which means "hardening" or "scarring." However, the causes and symptoms of these diseases are very different, as are the prognoses. 

(Perhaps you remember the "ice bucket challenge" during the summer of 2014, where people challenged others to dump buckets of ice over their heads? The point of those viral videos was to raise awareness and research funds for ALS.)

If you have MS, you might wonder whether you are more likely than the general population to develop ALS. In this breakdown of ALS vs. MS, find out more about these two conditions. 

What Is Multiple Sclerosis?

Multiple sclerosis is a chronic neurological disease in which the immune system attacks the myelin (fatty coating) covering the nerves in the central nervous system. There are many different theories about why this happens. A new theory called chronic cerebral vascular insufficiency (CCSVI) suggests that slow blood drainage from the brain (due to narrowed or deformed veins) results in iron deposits, which cause inflammation and lead to MS symptoms.

What Is Amyotrophic Lateral Sclerosis?

ALS is also a neurological disease. However, in ALS the neurons, themselves, degenerate (weaken and die). No one knows why this happens, although there is a small genetic component. ALS is not thought to be an autoimmune disease. The neurons that are affected by ALS are the motor neurons—the nerves that are responsible for controlling all voluntary movement.

The motor neurons in the brain and in the spinal cord begin to degenerate, then die, and are unable to send any messages to the muscles that they control. The muscles begin to atrophy (shrink) and weaken and the person eventually loses the ability to use these muscles.

Key Differences Between the Diseases

While there is some neuron loss in MS, it is primarily the myelin that is attacked. This slows down or disrupts the transmission of nerve signals. Remyelination often occurs, leading to scarring. After this happens, its function may be restored to some extent, although the process often leaves residual symptoms. In MS, pretty much any nerve in the central nervous system can be affected, so the range of symptoms of MS is vast.

In contrast, in ALS only the nerves that control voluntary muscle movement are typically involved, so symptoms usually involve a weakening of the arms and legs, trouble swallowing, speaking, and breathing (breathing is considered a voluntary muscle action, even though we do it subconsciously).

The disease course in ALS is usually very predictable, characterized by a steady decline and worsening symptoms. By contrast, there are four different types of MS. They are all very different in terms of progression and presentation. Some progress steadily, while other types are characterized by relapses and periods of remission. Within each type of MS, there is also a very broad spectrum of severity of symptoms and levels of disability.

The Bottom Line

Although they are both neurological diseases, ALS and MS are very different in many ways. It is very rare for someone who has MS to be diagnosed with ALS, as well. Having MS does not predispose you to ALS. 

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