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.
What are the different types of ataxia?
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.
What causes ataxia?
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.
Wilson's disease is autosomal recessive affecting the body's ability to metabolize copper and may lead to ataxia. It is an example of why classifying ataxia is sometimes difficult, since it is both a genetic and structural cause.
There are a group of patients with ataxia where the cause is not found and this ataxia is classified as idiopathic ataxia.
Celiac disease is an immune-mediated illness and is often thought only as a digestive disorder where the body cannot digest gluten. However, it may affect many other organs in the body. Gluten-associated ataxia may be one of the causes of sporadic idiopathic ataxia.
What are the signs and symptoms of ataxia?
The symptoms of ataxia will depend upon what part of the brain or body is affected. Common symptoms all involve lack of coordination:
- Difficulty walking with an unsteady gait, which is often wide-based and staggering. This can lead to stumbling and falling.
- Speech may be slurred and slow with an unusual rhythm to the words.
- Swallowing may be difficult and the patient may choke, especially when drinking liquids.
- Difficulty using the hands and fingers to button shirts, or pick up a fork or spoon to eat. Writing, keyboarding, sewing, and playing an instrument can be affected.
- Nystagmus is the term used to describe rapid involuntary eye movements where the eyes jerk back and forth. This can cause blurred vision and difficulty reading or moving the eyes from one word to the next.
- Fatigue is a common complaint, likely because the muscles of the body have to work harder to overcome the lack of coordination to perform their daily activities.
How is ataxia diagnosed?
History and physical examination are necessary for the clinical diagnosis of the disease process that results in ataxia. Questions may be asked about exposures to chemicals and other toxins. History may include delving into the family history asking about relatives who might have neurologic problems. The neurologic exam will be focused upon looking for muscle weakness and changes in sensation.
Laboratory tests (blood, urine, lumbar puncture) may look for electrolyte and chemical abnormalities and may screen for toxins and other poisons. CT scan or MRI of the brain and spinal cord may be required. Nerve conduction studies may be appropriate if there is concern for peripheral neuropathy (nerves outside the brain and spinal cord). If there is a potential for a familial or genetic cause, genetic testing may be appropriate.
There are many potential causes for ataxia and it may take time for a definitive diagnosis to be made. The primary health care professional may ask for consultation from an internal medicine specialist or neurologist to help identify the definitive diagnosis or underlying cause of the ataxia.
What is the treatment for ataxia?
The treatment of ataxia depends upon the underlying cause. Should the ataxia be found to be irreversible, physical and occupational therapy are the cornerstones of care, focusing on safety, mobility, maximizing function, and improving quality of life.
What is the prognosis for ataxia?
Ataxia is the sign of an underlying disease or illness and the prognosis depends upon the response to treatment of that underlying cause. For example, some causes of ataxia may be reversible (electrolyte imbalance, exposure to certain chemicals) so the prognosis is good while others (genetic, irreversible alcohol damage) may have a fair to poor prognosis.
Brain and Nervous System Resources
Medically reviewed by Joseph Carcione, DO; American board of Psychiatry and Neurology
Longo, Dan, et al. Harrisons's Principles of Internal Medicine. 18th ed. McGraw-Hill, 2011.