ALS (amyotrophic lateral sclerosis) is a disease of the parts of the nervous system that control voluntary muscle movement. In ALS, motor neurons (nerve cells that control muscle cells) are gradually lost. As these motor neurons are lost, the muscles they control become weak and then nonfunctional.

The word “amyotrophic” comes from Greek roots that mean “without nourishment to muscles” and refers to the loss of signals nerve cells normally send to muscle cells. “Lateral” means “to the side” and refers to the location of the damage in the spinal cord. “Sclerosis” means “hardened” and refers to the hardened nature of the spinal cord in advanced ALS.

In the United States, ALS also is called Lou Gehrig’s disease, named after the Yankees baseball player who died of it in 1941. In the United Kingdom and some other parts of the world, ALS is often called motor neurone disease in reference to the cells that are lost in this disorder.

Although no one knows for sure, reports suggest 12,000 – 15,000 people in the United States have ALS; every year, doctors tell about 5,000 people that they have it.

ALS usually strikes in late middle age (the late 50s is average) or later, although it also occurs in young adults and even in children, as well as in very elderly people. Some forms of ALS have their onset in youth. Men are slightly more likely to develop ALS than are women. Studies suggest an overall ratio of about two men to every woman who develops the disorder.

Two treatments are approved for ALS in the United States:

• Riluzole, approved in 1995, may have a modest effect (approximately three months) on extending survival.
• Radicava, approved in 2017, may help slow the rate of functional decline.

The average life expectancy is three to five years after an ALS diagnosis. There is no cure.

What happens in ALS?

Motor neurons, the nerve cells that degenerate and lose function in ALS, are divided into two types: upper and lower.

• The upper motor neurons are located near the surface of the brain and exert control over the lower motor neurons, which are in the brainstem and the spinal cord.
• The lower motor neurons are directly attached to muscles through “wires” called axons. Bundles of these axons leave the spinal cord and extend out to the muscles. It’s these bundles that doctors are referring to when they talk about the “nerves.”

The function of lower motor neurons is straightforward. They send “go” signals to muscles. When these cells lose function in ALS, muscles atrophy (shrink) and become progressively weaker and eventually unable to contract, resulting in paralysis.

The lower motor neurons that control most of the muscles in the body are in the spinal cord. Those that control the muscles involved in speaking, swallowing and facial expression are in the brainstem. They’re sometimes called bulbar motor neurons, because the part of the brainstem that houses them has a bulblike shape. The term bulbar involvement means that the muscles of the face, mouth and throat are affected by the disease.

The upper motor neurons have more complex functions, making them more difficult to study. Therefore, there is not as much information about them, although new technologies are being developed to change this. These cells seem to exert complex control over the lower motor neurons. This control allows movements to be smooth, directed and varied in intensity. (For instance, they’re part of an elaborate system that allows a person to aim a hand at a glass of water, estimate its weight, pick it up, and use the right amount of force to lift it to his or her mouth, all while thinking about something else.)

When upper motor neurons are lost and lower motor neurons remain, movements are still possible but can become tight (spastic) and less precise.

In ALS, a combination of these effects is usually seen because both upper and lower motor neurons are losing function. People with ALS can have weak and atrophied muscles with tightness (spasticity).

Muscle twitches (called “fasciculations”) and cramps are common; they occur because degenerating nerves become irritable.

Loss of voluntary muscles can lead to an inability to walk, to swallow and to speak. Those in the advanced stages of ALS may become unable to eat, move, or breathe independently.

It’s important to note that the involuntary muscles, such as those of the heart, gastrointestinal tract, bowel and bladder, and those that regulate sexual functions are not directly affected in ALS. Hearing, vision and touch generally remain normal.

Mild cognitive impairment in ALS is not uncommon, and severe cognitive impairment, known as “dementia,” can also occur in a small fraction of people with the disease. Some with ALS may experience involuntary laughing or crying spells that are unrelated to their emotional state. Called involuntary emotional expression disorder, or “pseudobulbar affect,” this symptom can be treated with medication.

When to seek medical advice

Talk with your physician if you notice these early signs of ALS:

• persistent weakness or spasticity in an arm or leg, causing difficulty using the affected limb (limb onset)
• difficulty controlling speech or swallowing (bulbar onset)

It isn’t unusual for people to ignore such problems for some time at this stage, or to consult a physician who may at first be relatively unconcerned. However, the disease — if it’s truly ALS — generally spreads from one part of the body to another so that eventually the problem can no longer be ignored.

It’s at this point that people usually are referred to a neurologist, who will consider ALS among many other possible diagnoses.

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