Early signs and symptoms of ALS include:
- Difficulty walking, tripping or difficulty doing your normal daily activities
- Weakness in your leg, feet or ankles
- Hand weakness or clumsiness
- Slurring of speech or trouble swallowing
- Muscle cramps and twitching in your arms, shoulders and tongue
- Difficulty holding your head up or keeping a good posture
The disease frequently begins in your hands, feet or limbs, and then spreads to other parts of your body. As the disease advances, your muscles become progressively weaker. This weakness eventually affects chewing, swallowing, speaking and breathing.
However, ALS doesn't usually affect your bowel or bladder control, your senses, or your thinking ability. It's possible to remain actively involved with your family and friends.
In ALS, the nerve cells that control the movement of your muscles gradually die, so your muscles progressively weaken and begin to waste away.
ALS is inherited in 5 to 10 percent of cases. The other cases appear to occur randomly.
Researchers are studying several possible causes of ALS, including:
- Gene mutation. Various genetic mutations can lead to inherited ALS, which appears nearly identical to the noninherited form.
- Chemical imbalance. People with ALS generally have higher than normal levels of glutamate, a chemical messenger in the brain, around the nerve cells in their spinal fluid. Too much glutamate is known to be toxic to some nerve cells.
- Disorganized immune response. Sometimes a person's immune system begins attacking some of his or her body's own normal cells, which may lead to the death of nerve cells.
Protein mishandling. Mishandled proteins within the nerve cells may lead to a gradual accumulation of abnormal forms of these proteins in the cells, eventually causing the nerve cells to die.
Established risk factors for ALS include:
- Heredity. Five to 10 percent of the people with ALS inherited it (familial ALS). In most people with familial ALS, their children have a 50-50 chance of developing the disease.
- Age. ALS most commonly occurs in people between the ages of 40 and 60.
- Sex. Before the age of 65, slightly more men than women develop ALS. This sex difference disappears after age 70.
It may be that in some people ALS, is triggered by certain environmental factors.
Also, some studies examining the entire human genome (genome-wide association studies) found numerous genetic variations that people with familial ALS and some people with noninherited ALS had in common. These genetic variations might make people more susceptible to ALS.
Environmental factors under study that may modify a person's individual risk of ALS include:
- Smoking. Smoking cigarettes appears to increase a person's risk of ALS to almost twice that of a nonsmoker. The more years spent smoking, the greater the risk. However, quitting smoking can eventually lower the increased risk.
- Lead exposure. Some evidence suggests that exposure to lead in the workplace may be associated with the development of ALS.
Military service. Recent studies indicate that people who have served in the military are at higher risk of ALS. Exactly what about military service may trigger the development of ALS is uncertain, but it may include exposure to certain metals or chemicals, traumatic injuries, viral infections and intense exertion.
As the disease progresses, people with ALS experience complications, which may include:
Over time, ALS paralyzes the muscles needed to breathe. Some devices to assist your breathing are worn only at night and are similar to devices used by people with sleep apnea. For example, you may be given noninvasive positive pressure ventilation to assist with your breathing at night.
In the latter stages of ALS, some people choose to have a tracheostomy — a surgically created hole at the front of the neck leading to the windpipe (trachea) — to enable the full-time use of a respirator that inflates and deflates their lungs.
The most common cause of death for people with ALS is respiratory failure. On average, death occurs within three to five years after symptoms begin.
Most people with ALS will develop trouble speaking over time. This usually starts as some mild slurring of words, often intermittently, but progresses over time to be more severe. With time, speech becomes more difficult for others to understand, and people with ALS often rely on other communication technologies to communicate.
When the muscles that control swallowing are affected, people with ALS can develop malnutrition and dehydration. They are also at higher risk of getting food, liquids or saliva into the lungs, which can cause pneumonia. A feeding tube can reduce these risks.
Some people with ALS experience problems with memory and making decisions, and some are eventually diagnosed with a form of dementia called frontotemporal dementia.