What is ataxia?

Ataxia describes the lack of muscle coordination when a voluntary movement is attempted. It may affect any motion that requires muscles to work together to perform a function, from walking to picking up an object to swallowing.

Ataxia is a sign of an underlying medical problem and is not a disease.

The cerebellum is the region of the brain that is responsible for coordinating motion in the body. When the brain commands part of the body to move, electrical signals are transmitted through the spinal cord into peripheral nerves that then stimulate a muscle to contract, initiating movement. That part of the body also has sensory nerves that collect information from the environment about position and proprioception, where the body is in time and space. These signals return via the same peripheral nerves but through a different pathway in the spinal cord. The cerebellum takes this information, as well as input from vision from the eyes and balance from the vestibular system of the inner ear, to help smooth out purposeful movement. Failure of any one or more of these pathway components can lead to ataxia.

Cerebellar ataxia is caused by abnormalities and damage, either temporary or permanent, to the cerebellum. Sensory ataxia occurs when the dorsal columns of the spinal cord fail to function normally. They are responsible for carrying proprioception information from the body to the brain. Damage to parts of the brain that have to interpret the information may also cause sensory ataxia. Vestibular ataxia describes loss of balance because the vestibular canals fail to function properly.

Ataxia maybe inherited and caused by a genetic defect or it may be acquired due to structural damage to the cerebellum or spinal cord.

Genetic ataxia may be sex linked, meaning that the DNA and gene problem is located on an X or Y chromosome (the sex chromosomes) or it may be autosomal linked, where the abnormality is located on one of the other 23 pairs of chromosomes.

Spinocerebellar and episodic ataxias are examples of autosomal dominant ataxias. Friedreich ataxia and ataxia telangiectasia are autosomal recessive.

Structural damage to the brain may be caused by any lesion that decreases blood supply to or invades into brain tissue, cerebellum included. This may include trauma and bleeding, stroke or tumor, and multiple sclerosis.

Poisonings, chemical, electrolyte, hormonal abnormalities, and malnutrition are also potential causes that tend to globally affect brain and body function and may or may not be reversible. Alcohol is perhaps the most common poisoning to cause ataxia. Other causes include a variety of prescription medications including lithium and those medications used to treat seizure disorders. Recreational drugs like PCP, ketamine, and marijuana may cause ataxia. Mercury poisoning may cause ataxia. Vitamin B12 deficiency and hypothyroidism are other potential causes.

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Ataxia: Get Facts on This Disorder - MedicineNet