ALS, or amyotrophic lateral sclerosis, is a progressive disease that destroys the nerve cells controlling voluntary movement. Often called Lou Gehrig’s disease, it causes muscles throughout the body to weaken and eventually stop working as the motor neurons in the brain and spinal cord die off. There are roughly 33,000 people living with ALS in the United States, and that number is expected to rise more than 10% by 2030.
How ALS Affects the Body
Your body has two types of motor neurons that work together to produce movement. Upper motor neurons originate in the brain and send signals down the spinal cord. Lower motor neurons pick up those signals and relay them to muscles in your arms, legs, chest, and throat. In ALS, both types progressively degenerate and die. Without these nerve signals, muscles weaken, twitch, and eventually atrophy.
The underlying damage involves multiple overlapping processes at the cellular level: toxic overactivity of nerve signaling, buildup of misfolded proteins inside neurons, inflammation, energy failure within mitochondria (the cell’s power source), and disrupted transport systems that normally shuttle nutrients along nerve fibers. No single one of these mechanisms explains the whole disease, which is part of why ALS has been so difficult to treat.
Early Signs and Two Types of Onset
ALS typically starts in one of two ways. The more common form, limb onset, accounts for roughly 66% to 75% of cases. It begins with weakness in an arm or leg: difficulty gripping objects, tripping while walking, or a hand that feels clumsy. The weakness usually starts on one side and gradually spreads.
The less common form, bulbar onset, affects the muscles involved in speaking, swallowing, and breathing first. Early signs include slurred speech, a voice that sounds different, or trouble swallowing food. Bulbar onset tends to progress faster than limb onset, with survival often less than two years. Although ALS overall is slightly more common in men, bulbar onset appears to be somewhat more common in women.
Regardless of where symptoms begin, ALS eventually affects muscles throughout the body. It does not typically impair thinking, memory, or the senses, though a subset of people develop some cognitive or behavioral changes over time.
What Causes ALS
Most cases of ALS, around 90% to 95%, appear without a clear family history. These are called sporadic cases. The remaining 5% to 10% are familial, meaning a known genetic mutation runs in the family.
Researchers have identified mutations in more than 30 genes linked to familial ALS. Four genes account for the majority: C9orf72, SOD1, TARDBP, and FUS together explain about 55% of familial cases in people of European ancestry. Notably, about 7% of people with apparently sporadic ALS also carry variants in these same four genes, blurring the line between genetic and non-genetic forms of the disease.
For most people with sporadic ALS, the exact trigger remains unknown. Environmental exposures, military service, and intense physical activity have been studied as potential risk factors, but no single cause has been confirmed.
How ALS Is Diagnosed
There is no single blood test or scan that confirms ALS. Diagnosis relies on a neurologist documenting progressive weakness that involves both upper and lower motor neuron damage, while ruling out other conditions that could explain the symptoms. This process often takes months and involves multiple visits.
A key tool is electrodiagnostic testing, which uses small electrical impulses and needle electrodes to assess how well nerves and muscles communicate. The test looks for signs of nerve damage: abnormal electrical activity in muscles that have lost their nerve supply and unusually large signals from remaining motor neurons that are compensating for lost ones. MRI scans of the brain and spinal cord are typically performed to exclude other diagnoses like spinal cord compression or multiple sclerosis.
Diagnostic criteria have evolved over the years. The most recent framework, known as the Gold Coast criteria, requires progressive motor dysfunction, evidence of both upper and lower motor neuron damage in at least one body region, and investigations that rule out alternative diagnoses. These simplified criteria were designed to reduce diagnostic delays.
Survival and Disease Progression
ALS progresses at different rates in different people, but the overall trajectory is one of steady decline. Median survival from diagnosis is estimated at about 21 months, though this figure varies significantly. Some people live five years or longer. Older age at diagnosis is the strongest predictor of shorter survival. Bulbar onset also tends to carry a shorter timeline than limb onset.
As the disease advances, most people lose the ability to walk, use their hands, speak clearly, and eventually breathe without assistance. Respiratory failure is the most common cause of death. The speed of this progression, however, is highly individual. Some people remain relatively stable for a year or more before a period of faster decline, while others experience a more steady, gradual loss of function.
Treatment Options
No treatment can cure ALS or reverse motor neuron damage, but several therapies can slow progression or manage symptoms. Riluzole, the oldest approved medication, modestly extends survival by reducing nerve cell overactivity. Edaravone (sold as Radicava) is an antioxidant designed to slow functional decline in some patients.
The newest approved treatment, tofersen (Qalsody), represents a shift toward gene-targeted therapy. It is designed specifically for people whose ALS is caused by mutations in the SOD1 gene, a small subset of all cases. The drug works by blocking production of the harmful SOD1 protein. It is delivered through spinal injection every four weeks after an initial loading period. Long-term data from a phase 3 trial showed that roughly one-quarter of participants experienced stabilization of symptoms over about three years, with some showing improvements in grip strength and breathing capacity. Common side effects include headache, back pain, and pain at the injection site. A new trial is now testing whether tofersen can prevent or delay symptoms in people who carry the SOD1 mutation but have not yet developed ALS.
What Day-to-Day Care Looks Like
ALS care is best managed by a multidisciplinary team, and specialized ALS clinics coordinate many providers under one roof. A neurologist oversees the overall treatment plan and prescribes medications for symptoms like muscle stiffness, cramping, and excessive saliva. A physiatrist (rehabilitation physician) evaluates the need for equipment: braces, power wheelchairs, shower seats, and other devices that maintain independence as strength changes.
Physical and occupational therapists play a central role throughout the disease. A physical therapist helps with walking, balance, and safe movement around the home, while an occupational therapist focuses on daily tasks like eating, bathing, and dressing. As the disease progresses, these therapists introduce adaptive tools and strategies that can preserve independence longer than most people expect.
Breathing support becomes increasingly important. A pulmonologist and respiratory therapist monitor lung function regularly and introduce devices like non-invasive ventilators when breathing weakens. Shortness of breath during everyday activities, while lying flat, or during meals are signals that respiratory support may be needed. A dietitian or gastroenterologist helps manage nutrition, especially when swallowing becomes difficult, which can eventually require a feeding tube to maintain adequate calorie intake.
Speech-language pathologists help people maintain communication as speech muscles weaken, often introducing voice-banking technology early so that computerized speech devices can use a person’s own recorded voice. For many people with ALS, planning ahead for these transitions, while they still have the physical ability to participate in the process, makes a meaningful difference in quality of life as the disease progresses.