As people with multiple sclerosis (MS), a neurological disease, I think we are highly in tune with the completely crucial role that our central nervous system (brain and spinal cord) and our peripheral nerves play in keeping us functioning. (I would guess that most people without a neurological disorder give much thought to their nervous system at all, until something goes wrong.) One question that I have gotten from a couple of people pertains to the similarities and differences between ALS and MS. Some of these people have been worried that having MS (multiple sclerosis) makes them more likely to develop ALS (amyotrophic lateral sclerosis). Yes, both disease involve the nerves and the word "sclerosis," which means "hardening" or "scarring." However, the mechanisms, causes and symptoms of these diseases are very different, as are the prognoses.
What Are the Differences Between ALS and MS?
Multiple sclerosis (MS) 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 ideas as to why this happens. A new theory, called chronic cerebral vascular insufficiency (CCSVI), puts forth the idea 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.
ALS (amyotrophic lateral sclerosis or Lou Gehrig's disease) 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 in 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 to 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.
While there is some neuron loss in MS, it is primarily the myelin that is attacked. This slows down or disrupts transmission of nerve signals. Remyelination often occurs, leading to scarring, after which function may be restored to some extent, although often leaving 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 typically the nerves controlling voluntary muscle movement are involved, so symptoms usually involve 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 of symptoms. By contrast, there are four different types of MS, which are 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.
Although they are both neurological diseases, ALS and MS are very different in many ways. It should be added that it is very rare for someone with MS to be diagnosed with ALS as well: having MS does NOT predispose people to ALS.