DESCRIPTION
The term “ataxia” means “lack of coordination.” It’s not due to muscle weakness.
Nervous system problems can cause ataxia. For example, it can result from problems in the inner ear. Specifically, the vestibular apparatus is affected. This structure senses movements of the head.
Problems with sensory nerves can also cause ataxia. In this case, the brain does not receive important information. This information would tell it the position of arms and legs.
Finally, ataxia can be caused by problems in the cerebellum. This structure is in the back of the brain. It’s found near the base of the skull. The cerebellum processes information from:
- The motor command centers of the brain
- The eyes
- The inner ear
- The sensory nerves
This information allows it to fine-tune motor movements. That way, they are accurate and appropriate.
The cerebellum is very sensitive to:
- Certain medications
- Alcohol
It can be damaged by:
- Strokes
- Tumors
The immune system can also attack it.
Many genetic disorders affect cerebellar function. Sometimes these worsen over time.
The cerebellum also plays an important role in:
- Cognition
- Emotions
CAUSES
Cerebellar ataxia can have many causes. It helps to divide them based on how quickly they start.
Acute cerebellar ataxia (ACA)
With ACA, symptoms occur suddenly. They are very noticeable.
In children, ACA is commonly caused by eating or drinking a substance. Many medications and alcohol can have this effect.
Infections can cause inflammation in the cerebellum. They can be viral or bacterial. This can lead to ataxia as well.
Ataxia can also happen very rarely after an immunization. The immune system responds to the vaccine appropriately, but cross-reacts with the cerebellum. This type of ataxia happens much more rarely than ataxia caused by the disease the vaccine prevents.
Autoimmune processes can attack the cerebellum. They can cause ataxia too. (This is similar to multiple sclerosis.)
Subacute cerebellar ataxia
With this type of ataxia, symptoms develop slowly. They occur over:
- Minutes
- Hours
- Days
- Weeks
With infections, symptoms can develop over hours or days. Strokes can also occur. This can happen when:
- A clot blocks blood flow to the cerebellum. That flow contains oxygen. (This is called an ischemic stroke.)
- There is bleeding into the brain. (This is called a hemorrhagic stroke.)
Tumors in or near the cerebellum may grow slowly. They can gradually cause symptoms. One example is medulloblastoma.
Rarely, a tumor elsewhere in the body can trigger antibodies. An example of this is neuroblastoma. These antibodies can cross-react with the cerebellum. This can cause ataxia. In this situation, there may be other symptoms. These include:
- Chaotic eye movements (opsoclonus)
- Involuntary jerks (myoclonus)
This combination of symptoms is called opsoclonus-myoclonus-ataxia syndrome (OMAS).
Chronic and progressive cerebellar ataxia
Chronic cerebellar ataxia is long-lasting. Progressive cerebellar ataxia worsens over time.
Some children have developmental brain differences. These differences affect the cerebellum. They can cause ataxia. Some conditions like this are:
- Dandy-Walker malformation
- Rhombencephalosynapsis
- Chiari I malformation
Children born prematurely can have a brain injury. Specifically, their motor system can be injured. This can cause cerebral palsy (CP). One type of CP is ataxic CP.
Some children have congenital ataxia. As babies, they may have:
- Low tone (hypotonia)
- Motor delays
As they grow, two things become clear. The first is that their cerebellum does not work properly. The second is that they have signs of cerebellar ataxia.
Several genetic disorders can cause congenital ataxia. They can cause progressive ataxia too. Sometimes they mostly cause problems in the cerebellum. Other times, the issues are widespread.
With other genetic disorders, the body cannot break down a certain compound. It then builds up in the nervous system. This causes problems. Examples of these disorders include:
- Hexosaminidase deficiency (Tay-Sachs and Sandhoff disease)
- Problems with cholesterol metabolism (Niemann-Pick type C)
- Copper metabolism (Wilson disease)
- White matter disorders (leukodystrophies like metachromatic leukodystrophy)
Every person has two copies of each gene. An error in one copy can sometimes cause a problem. (This error is also called a spelling change or mutation.) These disorders are “autosomal dominant.”
These diseases are often called “spinocerebellar ataxias.” They are also known as SCAs. The main symptom is cerebellar ataxia. These go by numbers. (For example, SCA1, SCA2, SCA3, SCA6, SCA7, and so forth.)
Many of the SCAs are caused by a specific genetic change. It is called a triplet repeat expansion. This tends to cause progressive symptoms. These conditions can be life-limiting.
Other SCAs are caused by more conventional genetic errors. They have more stable symptoms. One condition like this is SCA29.
For some disorders, both copies of the gene need to have a change. Otherwise, symptoms do not occur. These are “autosomal recessive” disorders.
This means that each parent is a carrier of the disorder. However, they do not have symptoms. This is because they have one working copy of the gene. It prevents symptoms from developing.
When progressive ataxia starts before the age of twenty-five, the most common diagnosis is Friedreich ataxia (FA). FA is an autosomal recessive disorder. It is caused by triplet repeat expansions in the FRDA gene.
Other better-known ataxias like this are:
- Ataxia-telangiectasia (A-T)
- AOA1 and AOA2 (ataxia with oculomotor apraxia type 1 and type 2)
- ARSACS (autosomal recessive spastic ataxia of Charlevoix-Saguenay)
Episodic cerebellar ataxia
Sometimes, children can have attacks of ataxia. They can last for:
- Minutes
- Hours
- Days
They may not have any neurological issues between attacks.
One condition is called vestibular migraine. With this, children may have ataxia without a headache.
With some genetic conditions, the body may have trouble creating energy. Cells need this energy. These conditions are called mitochondrial disorders. They can cause episodes of ataxia.
Finally, there is a group of genetic disorders called “episodic ataxias.” With these, there are changes in key genes. These genes affect the function of the cerebellum. They cause:
- Dizziness
- Nausea
- Ataxia
- Headache (sometimes)
LABORATORY INVESTIGATIONS
When ataxia occurs suddenly, the blood is typically tested. The urine may be too. Tests look for signs of infection. They also look for abnormal levels of certain compounds. These include ammonia.
Children are usually screened for possible ingestions of:
- Medications
- Alcohol
- Drugs
The next step is usually magnetic resonance imaging (MRI). Images of the brain are taken. Sometimes the spine is imaged too. This helps rule out:
- Strokes
- Tumors
A lumbar puncture can be necessary. This is also called a spinal tap. It tests the cerebrospinal fluid (CSF). The doctor looks for signs of:
- Infection
- Inflammation
Sometimes, a child has ataxia that occurs suddenly. However, it does not get better quickly. Symptoms remain after days or weeks.
In this case, the next steps include:
- Additional blood testing to look for:
- Vitamin deficiencies
- Metabolic disorders
- Checking for certain antibodies in:
-
-
- The blood
- The spinal fluid/CSF (sometimes)
-
- Looking for signs of a tumor in the rest of the body
For disorders that are chronic or progress slowly, genetic testing is typically needed for diagnosis.
Resources
The National Ataxia Foundation’s vision of a world without Ataxia will be accomplished through its primary programs of funding Ataxia research, providing vital programs and services for Ataxia families, and partnering with pharmaceutical companies in the search for treatments and a cure. NAF offers many educational resources for Ataxia, including a comprehensive library of brochures, fact sheets, and books. NAF oversees the Parents of Kids with Ataxia private Facebook group, which currently has over 800 members.
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