ALS, or amyotrophic lateral sclerosis, is a progressive neurological disease that destroys the motor neurons responsible for controlling voluntary muscle movement. Once called Lou Gehrig’s disease, ALS causes muscles throughout the body to weaken, waste away, and eventually stop working entirely, including the muscles that control breathing. An estimated 33,000 people in the United States are living with ALS, and that number is projected to rise above 36,000 by 2030.
How ALS Affects the Body
Motor neurons are nerve cells that run from the brain through the spinal cord and out to muscles throughout the body. They carry the signals that tell your muscles to move. In ALS, both upper motor neurons (in the brain) and lower motor neurons (in the spinal cord) progressively degenerate and die. When they stop sending messages, the muscles they control begin to weaken, twitch, and shrink.
This process is irreversible. Over time, ALS strips away the ability to walk, use your hands, speak, swallow, and breathe. The disease does not typically affect the senses: sight, hearing, taste, touch, and smell remain intact. Bladder and bowel control are also usually preserved. What makes ALS particularly cruel is that many people remain cognitively aware as their body loses function, though some do develop changes in thinking or behavior as the disease progresses.
Early Symptoms and How They Vary
ALS shows up differently depending on which motor neurons are affected first. About 70% of people develop what’s called limb-onset ALS, where the first signs are weakness or clumsiness in an arm or leg. You might notice trouble buttoning a shirt, tripping while walking, or a weakening grip. Muscle twitching and cramping are common early signs.
The remaining 30% develop bulbar-onset ALS, which initially targets the muscles controlling speech and swallowing. Slurred speech, a hoarse or breathy voice, and difficulty swallowing food are the hallmarks. Bulbar-onset ALS tends to be more aggressive, with an average disease duration of about 29 months compared to roughly 52 months for limb-onset cases.
Regardless of where it starts, ALS spreads. Nearly 85% of people who begin with limb symptoms eventually develop speech and swallowing difficulties as well. The disease is relentlessly progressive, meaning symptoms only worsen over time.
What Causes ALS
For the vast majority of people, the cause remains unknown. About 90% to 95% of cases are considered sporadic, meaning they occur without a clear family history. The remaining 5% to 10% are familial, linked to inherited genetic mutations. About two-thirds of people with familial ALS carry mutations in known ALS genes, which means more genetic culprits likely remain undiscovered. Interestingly, roughly 10% of people with sporadic ALS also carry a mutation in a gene previously linked to the disease, blurring the line between the two categories.
Environmental and occupational factors also appear to play a role. U.S. military veterans have a notably higher risk of developing ALS compared to civilians, with risk increasing, sometimes doubling, based on deployment history and total years of service. Exposure to herbicides, pesticides, certain metals, hydrocarbon solvents, and burn pit smoke are all associated with higher ALS rates. Among civilians, occupations involving regular exposure to chemicals or exhaust, such as truck driving, also carry elevated risk. Gulf War veterans have been particularly affected, with a striking 85% of postwar ALS cases in one study occurring in veterans under age 45.
How ALS Is Diagnosed
There is no single blood test or scan that confirms ALS. The diagnosis is fundamentally clinical, meaning doctors piece it together from a physical exam, symptom history, and a process of ruling out other conditions that can mimic the disease.
The current standard is the Gold Coast criteria, developed by an international panel of neurologists in 2019 to simplify what had been an unnecessarily complex diagnostic process. The core requirements are progressive loss of motor function, evidence of both upper and lower motor neuron damage in at least one body region, and test results that exclude other explanations. Electromyography, a test that measures the electrical activity of muscles, plays an important supporting role by detecting patterns of nerve damage that are characteristic of ALS.
One emerging tool is a blood marker called neurofilament light chain, a protein released when nerve fibers are damaged. Levels of this protein are significantly elevated in people with ALS compared to healthy individuals, with one study finding it could distinguish ALS from healthy controls with about 89% sensitivity and 89% specificity. Higher levels also correlate with faster disease progression, making it potentially useful for both diagnosis and predicting outcomes. This biomarker was central to the approval of one of the newest ALS treatments.
Life Expectancy and Prognosis
ALS carries a sobering prognosis. In a large population study spanning 42 years, the median follow-up after diagnosis was just 1.4 years. Roughly 37% of patients died within the first year, and nearly 72% had died within three years. About 10% of people with ALS have a slowly progressive form and survive 10 years or longer, but they are the exception.
Several factors influence how quickly the disease progresses. Bulbar-onset ALS typically moves faster, with survival often under two years from diagnosis. Younger age at onset and limb-onset presentation tend to carry a somewhat better outlook. Breathing support, particularly non-invasive ventilation, has a meaningful impact on survival, which is covered below.
Treatment and Supportive Care
No treatment can stop or reverse ALS. The therapies that exist aim to slow progression, manage symptoms, and extend life. The best-known medication works by reducing nerve cell damage through a mechanism that limits excessive signaling between neurons. A newer intravenous treatment targets a specific type of cell damage called oxidative stress. Both offer modest benefits in slowing functional decline.
In 2023, the FDA approved a treatment specifically for people whose ALS is caused by a mutation in the SOD1 gene, a small subset of patients. This drug works by blocking the genetic instructions that produce the harmful SOD1 protein. It was approved under an accelerated pathway based on its ability to reduce a blood marker of nerve damage, with ongoing studies tracking whether that translates into meaningful clinical improvement.
Supportive care, however, makes the biggest day-to-day difference. Non-invasive ventilation, a type of breathing support delivered through a mask, is one of the most impactful interventions available. People with ALS who use it have a reported median survival of 21 to 48 months from symptom onset, compared to just 8 to 15 months for those who don’t. It also reduces hospitalizations and improves quality of life. Effectiveness depends heavily on proper setup and management, which is why expert-led multidisciplinary clinics, where neurologists, pulmonologists, speech therapists, physical therapists, and nutritionists work together, produce better outcomes than fragmented care.
Other supportive measures include feeding tubes to maintain nutrition when swallowing becomes unsafe, speech-generating devices as verbal communication declines, and physical and occupational therapy to preserve mobility and independence for as long as possible. Assisted coughing techniques help clear the airway and reduce the risk of respiratory infections, which are a leading cause of death in ALS.
Who Gets ALS
ALS can affect anyone, but it is not evenly distributed. It is slightly more common in men than women, and most people are diagnosed between the ages of 55 and 75. The CDC estimates that U.S. prevalence will grow more than 10% between 2022 and 2030, driven largely by an aging population. White and non-Hispanic individuals are diagnosed at somewhat higher rates, though this may partly reflect disparities in access to specialized neurological care and diagnostic resources rather than true differences in disease occurrence.