When symptoms of amyotrophic lateral sclerosis (ALS), such as weakness and a loss of muscle mass, start in the limbs, doctors refer to the condition as limb onset ALS.

ALS is a progressive condition that gradually kills the nerve cells that control muscle movement.

ALS is a rare condition. It affects the motor neurons, which are nerves in the brain and spinal column that control movement. Over time, this condition progresses, reducing control over the muscles and leading to weakness and muscle tissue loss.

Healthcare professionals classify different progressions of ALS by where the early symptoms begin, including:

  • limb onset ALS, the most common type, which starts in the arms and legs
  • bulbar onset ALS, which affects the muscles responsible for speaking and swallowing during the onset
  • respiratory onset ALS, a rare type that affects the lungs before other areas

It is not possible to reverse or cure ALS.

This article explains the symptoms, causes, and treatments for limb onset ALS.

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Limb onset ALS means the first symptoms of ALS affect the arms or legs. Some healthcare professionals refer to it as spinal onset ALS, meaning that the motor neurons in the spine — or lower motor neurons — are the first to start dying.

During the first stage of ALS, symptoms usually affect either the limbs or the ability to speak or swallow. For people with limb onset ALS, this means that symptoms start in the arms or legs before progressing to other parts of the body.

Most people with ALS have limb onset ALS. A 2017 report estimated that 74% of individuals with ALS have the limb onset type. Weakness in the arms or legs is often the first sign of ALS.

Learn more about ALS.

The causes of all forms of ALS are unclear. Around 5–10% of people with ALS have genes linked to the condition.

However, most people with ALS have a sporadic type, meaning that it can occur with no family history. Some variations in genes may increase a person’s likelihood of getting the condition without being a direct cause.

Factors that may contribute to nerve damage in ALS include:

  • Oxidative stress: This occurs when there are more free radical molecules causing damage than antioxidants, which reduce their toxic effects.
  • Mitochondrial dysfunction: The energy source inside cells may be atypical, which could cause ALS to develop or progress.
  • Microglia: These are immune cells that operate in the nervous system. They protect the body but can cause nerve damage, which has potential links to ASL.
  • Excess glutamate around nerve cells: Glutamate carries messages between nerve cells. However, excess glutamate can affect how nearby nerves function. It may be that the cells of people with ALS cannot efficiently move glutamate away.
  • Toxins: While more research is necessary to confirm the exact toxins involved, exposure to Cyanobacteria and poisonous nuts from the cycad trees on Guam may have a connection to an increased risk of ALS.

Certain people may be more at risk of developing ALS. However, having risk factors does not mean a person will develop the condition. Some risk factors for ALS include:

  • having an immediate relative with ALS
  • being male between the ages of 55–75
  • having served in the military, with exposure to lead, pesticides, and other environmental toxins

Read about the age of onset for ALS.

Limb onset ALS often does not cause any pain. Instead, people may notice a loss of function and muscle symptoms, including:

  • muscle weakness, including grip
  • muscle tightness
  • brief periods of rapid, visible twitching

These issues may affect daily tasks. A person may also feel fatigued, have balance issues, or stumble while walking.

Symptoms commonly affect both sides equally. They often start in the arms or legs before progressing. These symptoms may be slight and difficult for a doctor to diagnose at the onset.

Learn more about early ALS symptoms.

Advanced symptoms

ALS is a progressive disease. This means the symptoms will eventually reach an advanced stage that severely impairs a person’s quality of life.

The loss of muscle strength eventually makes someone unable to walk. Later in the progression of the disease, people often develop slurred speech before losing the ability to chew and swallow food. This can lead to malnutrition.

Limb onset ALS progresses more slowly to speech difficulties and eating problems than other forms of ALS.

Other symptoms people may experience include:

  • drooling due to excess saliva that results from swallowing less
  • yawning excessively, even without feeling tired
  • sudden episodes of laughter or crying that do not relate to a specific trigger, known as pseudobulbar affect
  • dementia symptoms in some people with ALS, including problems with planning, communication, and concentration, as well as behavior changes
  • breathing problems due to progressive lung muscle damage, including breathing difficulties at night or while lying down

Read more about ALS stages.

There is no cure for ALS. Treatment focuses on relieving symptoms and preserving quality of life.

Treatment options for ALS may include:

  • breathing support
  • assistive devices, such as a cane or wheelchair
  • medications to address specific symptoms

People with ALS may also receive nutritional advice, such as what foods to eat and supplemental drinks to offset any malnutrition.

Read about ALS diagnosis and treatment plans.

Most people with ALS have a life expectancy of 3–5 years after diagnosis, while some with the condition live longer. According to a 2023 review, roughly 30% of those with ALS survive for at least 5 years after a diagnosis. Additionally, 10–20% survive for 10 or more years.

People with limb onset ALS often have a more positive outlook than those with bulbar onset ALS.

The following are answers to questions people frequently ask about ALS.

How fast does limb onset ALS progress?

ALS progresses differently in different people. However, a 2022 study found that a type of limb onset disease in the legs called flail leg syndrome took an average of 2 years to spread from the legs to other areas.

The study authors acknowledged that this was slower than most people who have low limb onset ALS. In turn, a 2023 review suggested that limb onset ALS has a slower progression to other symptoms than other ALS types.

What is the difference between bulbar and limb onset ALS?

In limb onset ALS, symptoms start in the arms or the legs. In people with bulbar onset ALS, the muscles that affect speech and swallowing start to lose function first.

Does ALS start in the extremities?

Limb onset ALS in the arms often starts in the dominant hand, according to a 2020 review. In the lower body, this usually starts in the muscles around the shin bone.

Limb onset ALS occurs when motor neurons start to die in the limbs before other areas, such as the muscles controlling chewing or breathing.

This type of ALS has a more positive outlook and slower progression than other types. It is the most common form of ALS and might cause weakness in the arms, shoulders, and ankles. A person can also experience muscle symptoms, such as twitching or cramping.

Treatment, such as breathing support, medications, and mobility support, can improve comfort and quality of life. However, ALS is not cureable. People with ALS most often have a life expectancy of 3–5 years after diagnosis.