ALS, or amyotrophic lateral sclerosis, is a progressive neurological disease that destroys the nerve cells responsible for voluntary movement. Often called Lou Gehrig’s disease, it affects roughly 33,000 people in the United States at any given time, with a prevalence of about 9.9 per 100,000 people. The disease gradually takes away the ability to walk, speak, eat, and eventually breathe.
How ALS Affects the Body
Your brain controls movement through two types of motor neurons. Upper motor neurons run from the brain down through the spinal cord, while lower motor neurons extend from the spinal cord out to individual muscles. ALS attacks both types simultaneously. As upper motor neurons die, muscles become stiff and reflexes become overactive. As lower motor neurons die, muscles weaken, shrink, and begin to twitch involuntarily.
The result is a body that progressively loses the ability to carry out intentional movement. Muscles that don’t receive nerve signals begin to waste away, a process called denervation atrophy. Critically, ALS does not typically affect thinking, memory, or the senses. Most people with ALS can still see, hear, feel touch, and think clearly even as their body loses function, though a subset of patients do experience some cognitive changes.
Early Symptoms and How They Vary
ALS doesn’t look the same in everyone. The earliest sign is usually slight weakness in one limb. About 75% of cases begin this way, called limb-onset ALS. A person might notice unexplained tripping from a subtle foot drop, or mild difficulty with tasks requiring fine finger movements like writing, buttoning a shirt, or turning a key. Muscle cramps and visible twitching in the shoulder, upper arm, or forearm often accompany this early weakness. Stiffness in the fingers or leg muscles on one side is another common first sign.
In roughly 25% of cases, the disease starts in what’s called bulbar-onset ALS, meaning it first affects the muscles of the mouth, tongue, and throat. These patients notice difficulty speaking clearly, trouble swallowing, or problems managing saliva. A doctor examining the tongue may see it looks shrunken and weak, with visible twitching. In rare cases, ALS can first appear as weakness in the neck muscles (causing the head to drop forward), the trunk muscles, or even the diaphragm, leading to early breathing difficulties before limb weakness becomes obvious.
Regardless of where symptoms start, the disease eventually spreads to other body regions. What begins as a weak hand or slurred speech will, over time, affect more and more muscle groups.
What Causes ALS
For most people diagnosed with ALS, there is no clear cause. About 90 to 95% of cases are considered sporadic, meaning they occur without a family history of the disease. The remaining 5 to 10% are familial, passed down through inherited gene mutations.
The most common genetic mutation linked to ALS is a repeat expansion in the C9orf72 gene, which shows up in 5 to 10% of all ALS cases and up to 34% of familial cases. Mutations in the SOD1 gene and the TDP-43 gene are also well-established causes. However, current genetic knowledge mostly explains the familial cases. The vast majority of sporadic cases still lack a reliable genetic explanation, which makes predicting who will develop ALS extremely difficult.
How ALS Is Diagnosed
There is no single blood test or scan that confirms ALS. Diagnosis is still based primarily on clinical evaluation: a neurologist looking for signs of both upper and lower motor neuron damage. The most current diagnostic framework, known as the Gold Coast criteria, requires three things: a documented history of progressive motor decline after previously normal function, evidence of both upper and lower motor neuron involvement in at least one body region, and thorough testing to rule out other conditions that can mimic ALS.
That last requirement is a significant part of the diagnostic process. Neurologists use nerve conduction studies, electromyography (EMG, which measures electrical activity in muscles), blood work, and brain or spinal imaging to exclude other diseases. EMG findings can count as evidence of lower motor neuron damage even before clinical signs are visible, which helps with earlier detection. Still, the path from first symptoms to a confirmed diagnosis often takes months, partly because early ALS can resemble other, more common conditions.
Disease Progression and Prognosis
ALS is a fatal disease. Average survival ranges from 2 to 5 years after symptoms first appear, with a median of about 2 to 3 years from onset. After a formal diagnosis, median survival in large registry studies is roughly 18 to 21 months, reflecting the delay that often occurs between symptom onset and diagnosis.
There is encouraging, if modest, evidence that survival times are slowly improving. Data from a long-running Italian registry showed that patients diagnosed between 2013 and 2018 had a measurable survival advantage compared to earlier periods, with a roughly 10% increase in median survival over two decades. Researchers attribute this improvement largely to better coordinated care at specialized treatment centers rather than to any breakthrough medication.
Doctors track the progression of ALS using a standardized rating scale that evaluates 12 specific functions across four categories: bulbar function (speech, swallowing, saliva management), fine motor skills (handwriting, handling utensils, dressing), gross motor function (walking, climbing stairs, turning in bed), and breathing. Each function is scored from 4 (fully normal) down to 0 (complete loss), giving clinicians and patients a concrete way to monitor changes over time and adjust care accordingly.
Treatment Options
No existing treatment can stop or reverse ALS, but a few medications can modestly slow its progression. Riluzole was the first drug approved for ALS and remains the most widely used. It works by reducing excess signaling from a brain chemical called glutamate, which in high concentrations is toxic to motor neurons. Clinical evidence shows it extends survival by several months.
Edaravone, approved more recently, takes a different approach. It acts as an antioxidant, neutralizing harmful molecules called free radicals that contribute to nerve cell damage. It appears most effective in patients with early-stage disease who are still progressing relatively slowly.
For the small percentage of patients whose ALS is caused by a mutation in the SOD1 gene, a targeted therapy called tofersen is available. This drug is injected into the spinal fluid and works by intercepting the genetic instructions for the defective SOD1 protein, reducing the amount of toxic protein the body produces. It represents a shift toward precision medicine in ALS, though it only applies to a narrow subset of patients.
The Role of Multidisciplinary Care
Beyond medication, the single most impactful intervention for people with ALS is coordinated care from a team of specialists. A comprehensive ALS clinic typically includes neurologists, respiratory specialists, gastroenterologists, rehabilitation doctors, physical therapists, occupational therapists, speech-language pathologists, nutritionists, social workers, psychologists, and specialist nurses. Genetic counselors and case managers have become common additions in recent years.
This isn’t just a matter of convenience. Patients who receive care through a specialized multidisciplinary ALS clinic live measurably longer. One study from Ireland found that attending a national ALS clinic improved survival by 7.5 months and reduced one-year mortality by 30%. Italian data showed that specialized clinics also reduced hospital admissions and shortened hospital stays. The benefits come from catching complications early, managing nutrition and breathing support proactively, and adapting assistive devices as needs change. National and regional ALS associations also play a significant role, connecting patients and families with support services and resources throughout the course of the disease.
Who Gets ALS
ALS can strike at any age, but prevalence climbs sharply with age. The highest rates occur in people 66 and older, where prevalence reaches 30.4 per 100,000. As the U.S. population ages, the total number of cases is expected to grow through at least 2030. Men are somewhat more likely to develop ALS than women, though this gap narrows in older age groups. Beyond age and sex, no widely confirmed environmental risk factors have been established for sporadic ALS, making it one of the more unpredictable diagnoses in neurology.