ALS stands for amyotrophic lateral sclerosis, a progressive neurological disease that destroys the nerve cells responsible for voluntary movement. Each word in the name describes what happens in the body: “amyotrophic” comes from Greek roots meaning “no muscle nourishment,” “lateral” refers to the area of the spinal cord where the affected nerve pathways sit, and “sclerosis” means scarring or hardening of those pathways as they degenerate. You may also hear ALS called Lou Gehrig’s disease, after the baseball player diagnosed in 1939, or motor neuron disease, the term more commonly used outside the United States.
What the Name Tells You About the Disease
The medical terminology is unusually descriptive. Your brain controls movement through two sets of nerve cells. Upper motor neurons in the brain send signals down to lower motor neurons in the spinal cord, which then relay those signals to your muscles. In ALS, both sets of neurons progressively die.
When lower motor neurons stop working, your muscles no longer receive the electrical signals they need to contract. Without that stimulation, the muscles weaken and physically shrink, a process called atrophy. That’s the “amyotrophic” part. When upper motor neurons fail, the connection between brain and spinal cord breaks down, causing muscle stiffness and exaggerated reflexes. The “lateral sclerosis” part refers to the scarring that develops along the sides of the spinal cord as these upper motor neuron pathways harden and degrade.
How ALS Typically Starts
ALS shows up in one of two ways. The more common form is limb onset, where weakness begins in the arms, hands, or legs. Early signs include a weakening grip, muscle twitching or cramping, fatigue, poor balance, or stumbling while walking. Symptoms usually start on one side or in one limb before spreading.
The less common form is bulbar onset, which affects the muscles of the face and throat first. People with bulbar-onset ALS notice slurred speech, hoarseness, and difficulty chewing or swallowing. Choking while eating is a frequent early complaint. Regardless of where it starts, ALS eventually spreads to affect muscles throughout the body. It does not affect thinking or memory in most cases, though a subset of patients develop cognitive changes.
Who Gets ALS
ALS is rare. The U.S. incidence is about 1.44 people per 100,000, based on CDC registry data. It most commonly appears between ages 55 and 75, though younger people can develop it too. Men are slightly more likely to be diagnosed than women.
Most cases, roughly 80 to 90 percent, are sporadic, meaning they occur without a clear family history. The remaining cases are familial, passed through inherited gene mutations. Research from a long-running Irish population study found that the true rate of familial ALS may be as high as 20 to 30 percent when extended family histories and genetic testing are factored in. Among known genetic causes, a mutation called C9orf72 dominates, accounting for the vast majority of identifiable inherited cases.
How ALS Is Diagnosed
There is no single blood test or scan that confirms ALS. Diagnosis relies on clinical evaluation: a neurologist looks for signs of both upper and lower motor neuron damage, tracks how symptoms progress over time, and systematically rules out other conditions. About 12 percent of people initially suspected of having ALS turn out to have something else, most commonly spinal cord compression, peripheral nerve damage, or inflammatory muscle disease.
Nerve conduction studies and electromyography (a test that measures electrical activity in muscles) play a central role in confirming the pattern of nerve damage. Because no definitive biomarker exists, diagnostic criteria have been refined over decades to catch ALS earlier. The most recent set, introduced in 2020, simplified the process and improved the ability to identify ALS in its early stages, when symptoms may still be subtle or confined to one body region.
Progression and Prognosis
ALS is progressive, meaning it worsens over time. The rate varies widely between individuals. The average survival after diagnosis is about three years, but that number can be misleading. Some people decline rapidly within months, while roughly 10 percent live ten years or more. Factors that influence survival include where symptoms start (bulbar onset tends to progress faster), age at diagnosis, and how quickly respiratory muscles are affected.
As the disease advances, it moves through recognizable stages. Early on, weakness may be limited to one area. Over time it spreads to other limbs, the trunk, and eventually the muscles that control breathing and swallowing. Most people with ALS ultimately need assistance with daily activities, communication, and respiratory support.
Treatment and Respiratory Support
No cure exists for ALS. Two medications have been approved by the FDA, but both offer limited benefit. One works by reducing nerve cell damage from excess signaling, and the other acts as an antioxidant to slow cellular stress. Neither reverses the disease or dramatically extends life on its own.
Breathing support is one of the most impactful interventions. A mask-based ventilator, used especially at night, can be started when breathing muscles begin to weaken. In a randomized trial published in The Lancet Neurology, patients with relatively preserved speech and swallowing function who used this type of ventilation lived a median of 205 extra days compared to those who did not, with quality of life maintained for most of that time. For patients with more advanced bulbar symptoms, the ventilation still improved comfort and symptom burden but did not extend survival.
Beyond medication and breathing support, ALS care involves a team approach: physical and occupational therapy to maintain function as long as possible, speech therapy and communication devices when speaking becomes difficult, nutritional support when swallowing declines, and adaptive equipment to preserve independence. The goal at every stage is to manage symptoms and maintain quality of life rather than to treat the underlying disease, which continues to progress.