What Is Guamanian ALS?

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People who lived on the island of Guam were disproportionately affected by ALS (amyotrophic lateral sclerosis) in the late 1940s. The disease, now known as lytico-bodig in Guam, presents as a combination of ALS and Parkinson’s dementia symptoms. It is often referred to as ALS and Parkinsons-dementia complex (ALS/PDC).

The first high incidence rate of the disease occurred during World War II when ALS in Guam was more prevalent than elsewhere in the world.

This article discusses the symptoms, timelines, possible causes, and prognosis associated with the disease.  

Older couple speaking to nurse

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Guamanian ALS Symptoms

Guamanian ALS, or ALS/PDC, presents with symptoms of all three disorders, which can include:

  • Muscle twitches in the arms, legs, shoulders, or tongue
  • Muscle weakness, cramps, stiffness, and tightness
  • Slurred or muffled speech
  • Difficulty chewing, swallowing, talking, or forming sentences
  • Immobility as the disease worsens
  • Difficulty breathing
  • Memory changes
  • Difficulty concentrating
  • Impaired sense of judgment
  • Difficulties with interpreting visual information
  • Visual hallucinations
  • Paranoia and delusions
  • Mood changes, such as depression, anxiety, and irritability
  • Sleep changes that include rapid eye movement sleep disorder or excessive daytime drowsiness

Timeline for ALS/PDC:

The cluster of ALS/PDC peaked in Guam during and shortly after World War II and decreased steadily from the 1950s to the 1980s. Since then, fewer cases have been reported. ALS/PDC has essentially disappeared from the island of Guam, so it is hard to conduct further research on the disease.


The cause of ALS/PDC is hard to determine because of the lack of new cases in the region. However, the study of the disease thus far has come to one theory of its cause: neurotoxicity caused by β-N-methylamino-L-alanine (BMAA), a naturally occurring diamino acid found in cyanobacteria and certain microorganisms.

The amino acid is found in blue-green algae and has been shown to cause motor neuron disease when tested in animal studies. Specific plants used in food and medicine in Guam, known as cycad plants, have high levels of BMAA. Fruit bats are also thought to accumulate high levels of BMAA and pass it on to humans when consumed as food.

Since then, limited and controversial research has suggested that BMAA accumulation and consumption can increase a person’s risk of developing neurodegenerative disorders such as ALS, Alzheimer's disease, and Parkinson’s disease.

Other research suggests that the flour made from the seeds of the cycad plant that haven’t been adequately detoxified contributed to the onset of ALS/PDC. When the seeds still contain toxins, they act as a poison in the body and lead to neurodegeneration.

Why Is ALS/PDC Disappearing?

Though the evidence for the disappearing disease isn’t well documented, research suggests that knowledge surrounding the consumption of cycad plants plays a role. During World War II, soldiers would have to camp in the jungle and possibly rely heavily on cycad plants as a primary food source. After the war, more information surrounding the detoxification of the plant’s seeds became available, and cases have since steadily declined.  


During the Guamanian ALS/PDC endemic, diagnostic processes may have been different than they are now. Currently, medical providers follow what is known as the El Escorial or Airlie House criteria to diagnose ALS. These criteria were not developed until 1991. Because of that, they couldn't be used during the cluster of cases in the 1940s.

Doctors relied heavily on symptom collection, healthy history, and other diagnostic tools available to them at the time. Cognitive assessments had been around for decades at that point and were likely for judging the level of impairment in people with ALS/PDC. Magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), and other tests for diagnosing ALS and Parkinson's dementia today were not around during the Guam cluster.

Currently, the tests that can work to diagnose ALS/PDC include:

  • Neuroimaging tests such as an MRI or angiography (MRA)
  • Single-photon emission computed tomography (SPECT)
  • Cognitive assessments, such as the Mini-Mental State Examination (MMSE), Raven’s Coloured Progressive Matrices (RCPM), the paired-associate learning test (PALT), the Frontal Assessment Battery (FAB) test, and the Standard Language Test of Aphasia (SLTA)

The cognitive tests are designed to test for brain function, psychomotor speed, verbal fluency, short-term memory, and frontal lobe function. The SLTA tests for aphasia, which is a disorder that causes a person to lose their ability to communicate with others.

In some cases, an autopsy can help diagnose the disease.

When Was ALS/PDC Discovered?

The first identification of ALS came in 1869. However, PDC wasn’t established as a disease until 1961. To diagnose cases of ALS/PDC in Guam, the National Institute of Neurological Disorders and Stroke research center opened in 1956 to provide medical testing for those exhibiting disease symptoms. 


Treatment for Guamanian ALS focuses on managing symptoms. Because it is progressive and there is no cure for it, treatment can only improve a person’s quality of life before they succumb to the disease. During the Guam cluster, medicines were not as readily available as they are today.

Current ALS and PDC treatments, such as cholinesterase inhibitors and levodopa/carbidopa, were not invented until long after the 1940s.

Physical, occupational, and speech therapy were all well established by the time the people of Guam started experiencing high rates of ALS/PDC. However, whether these treatments helped them cope with symptoms is unclear.

Currently, all of the treatments mentioned above can help treat the disease.


ALS/PDC is a fatal disease. When a person is diagnosed, treatment will prolong their life and keep symptoms at bay. Typically, people with the condition can expect to live anywhere from four to six years following their diagnosis.

For How Long Did the People of Guam Survive With ALS/PDC?

Research is unclear on the survival rates of people who had Guamanian ALS. Given that treatments were not as readily available, the length of time people lived with the disease may have been shorter compared to today.


Guamanian ALS, often referred to as ALS/PDC, is a neurodegenerative disease that affected much of the population of Guam during and shortly after World War II. People with the disease experienced the typical symptoms of ALS and Parkinson’s dementia. Though the cause of the disease isn’t clear, the leading theory is that people in Guam had consumed a large number of cycad plants.

The plant contained a neurotoxin known as BMAA, leading to the degeneration of neurons and, eventually, disease. Diagnosing ALS/PDC wasn’t easy in the 1940s. In 1956, the National Institute of Neurological Disorders and Stroke opened a research center to help diagnose and treat those afflicted with the disease and understand more about it.

ALS/PDC is fatal, so treatment can only improve quality of life rather than cure it. That said, cases of Guamanian ALS have decreased significantly since the years following the war, and incidence rates have dropped to almost zero in recent years.

A Word From Verywell

The Guamanian ALS cluster that occurred on the island of Guam after World War II may seem like an isolated incident. However, other areas of the world, such as Kii, Japan, have experienced similar endemics.

The disease is now considered incredibly rare, so it’s highly unlikely that you will develop it at any point in your life. Because the amino acid suspected to cause the disease is found in blue algae and the cycad plant, keep yourself and your pets safe by avoiding consumption of those two plants.

Frequently Asked Questions

  • Why did the people of Guam develop ALS at such high rates?

    Guam is home to a specific plant known as the cycad. When not appropriately detoxified, this plant contains an amino acid called BMAA. It acts as a neurotoxin when consumed in high amounts, and people can develop ALS/PDC. During World War II, the people of the island of Guam relied heavily on the cycad plants for sustenance while they sought refuge in the jungle, which may have led to an increase in rates in the region.

  • How rare is Guamanian ALS?

    The highest number of Guamanian ALS cases occurred just after World War II. Nowadays, the disease is considered especially rare. It is not clear how many people still have it, but research indicates it has essentially disappeared from the island. 

  • Are there other names for Guamanian ALS?

    Though people who were diagnosed with Guamanian ALS exhibited the same symptoms found in typical ALS, they also experienced signs of another disease known as Parkinson’s dementia. That is why Guamanian ALS is often referred to as ALS/PDC. In Guam, the disease is referred to as lytico-bodig.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Angelica Bottaro
Angelica Bottaro is a professional freelance writer with over 5 years of experience. She has been educated in both psychology and journalism, and her dual education has given her the research and writing skills needed to deliver sound and engaging content in the health space.