Ataxia is a lack of muscle coordination which may affect speech, eye movements, the ability to swallow, walking, picking up objects and other voluntary movements. A person with persistent ataxia may have damage in the part of the brain that controls muscle coordination - the cerebellum. Ataxia may have several causes, including multiple sclerosis, a head injury, alcohol abuse, stroke, cerebral palsy, a faulty gene, or a tumor. Ataxia may also be a symptom of incoordination linked to infections.
There are different types of ataxias including Friedreich's ataxia and spinocerebellar ataxia type 6. A less common type is ataxia telangiectasia. According to Ataxia UK, there are over 40 known forms of inherited ataxias - new forms continue to be identified as scientific techniques improve.
The International Ataxia Awareness Day is observed on September 25 each year.
The term ataxia may also be used more broadly to indicate a lack of coordination in a physiological process, such as optic ataxia (usually part of Balint's syndrome which includes a lack of coordination between visual inputs and hand movements), or ataxic respiration (uncoordinated respiratory movements, usually due to dysfunction of the respiratory centers of the medulla oblongata).
The English word "ataxia" comes from the Ancient Greek word ataksia meaning "disorder". The Ancient Greek word taksia means "order".
Types of ataxias
The following are some of the more common types of ataxias.
The cerebellum is involved in the assimilation of sensory perception, coordination and motor control
This is ataxia caused by a dysfunction of the cerebellum - a region in the brain which is involved in the assimilation of sensory perception, coordination and motor control. Cerebellar ataxia causes some basic neurological problems, such as:
- Floppiness (hypotonia).
- Lack of co-ordination between organs, muscles, limbs or joints (asynergy).
- Impaired ability to control distance, power, and speed of an arm, hand, leg or eye movement (dysmetria).
- Difficulty in accurately estimating how much time has passed (dyschronometria).
- An inability to perform rapid, alternating movements (dysdiadochokinesia).
How the patient is affected depends on which parts of the cerebellar are lesioned, and whether lesions occur on one side (unilateral) or both sides (bilateral).
If the vestibulocerebellum is affected the patient's balance and eye movement control will be affected. The patient will typically stand with feet wide apart in order to gain better balance and avoid swaying backwards and forwards (posterior-anterior oscillations). Even when the patient's eyes are open balance is difficult when the feet are together.
If the spinocerebellum is affected the patient will have an unusual gait, with unequal steps, sideways steps, and uncertain starts and stops. The spinocerebellum regulates body and limb movements.
If the cerebrocerebellum is affected the patient will have problems carrying out voluntary, planned movements. The head, eyes, limbs and torso may tremble as voluntary moves are carried out. Speech may be slurred, with variations in rhythm and loudness.
This is ataxia due to loss of proprioception. Proprioception is the sense of the relative position of neighboring parts of the body. It is a sense that indicates whether the body is moving with the required effort, and also where the various parts of the body are located in relation to each other. Even if I am blindfolded I know through proprioception if my arm is above my head or hanging down in front of me, by my side, or behind me.
A patient with sensory ataxia typically has an unsteady stomping gait, with the heel striking hard as it touches the ground with each step. Postural instability becomes worse in poorly lit environments. If a doctor asks the patient to stand with eyes closed and feet together his/her instability will clearly worsen. This is because loss of proprioception makes the patient much more reliant on visual data.
The patient may find it hard to perform smoothly coordinated voluntary movements with the limbs, trunk, pharynx, larynx, and eyes.
The vestibular system is affected. In acute (sudden) unilateral cases the patient may experience vertigo, nausea, and vomiting. In slow-onset chronic bilateral cases the patient may only experience unsteadiness, giddiness.
Causes of ataxia
Ataxia can be a symptom of another health condition, it can also be inherited or non-inherited.
This means the ataxia is caused by a genetic fault inherited either from the mother or father, or both. A faulty gene that is passed down through generations can cause cerebellar ataxia - in some cases its severity worsens from one generation to the next and the age of onset gets younger. This type of worsening inherited ataxia is known as anticipation.
The chances of inheriting ataxia from a parent depends on the type of ataxia that parent has. For a person to develop Friedreich's ataxia the faulty gene would need to be carried by both the mother and the father (recessive inheritance). Spinocerebellar ataxia, on the other hand, only requires one parent to carry the defective gene (dominant inheritance), and each of his/her offspring would have a 50% risk of developing the condition.
Even without a family history of ataxia some people may still develop the condition. In some cases, experts never find out what the cause was. The following procedures and circumstances can cause ataxia:
- Brain surgery.
- Head injury.
- Alcohol abuse.
- Drug abuse.
- Infections, such as chicken pox (usually goes away after infection has gone).
- A brain tumor.
- Exposure to toxic chemicals.
- Multiple sclerosis, cerebral palsy, and some other neurological conditions.
- Malformation of the cerebellum while the baby is still in the womb.
Symptoms of ataxia
Symptoms may vary depending on the severity and type of ataxia, of which there are many. If the ataxia is caused by an injury or another health condition, symptoms may emerge at any age, and may well improve and eventually disappear.
Initial ataxia symptoms usually include:
- Poor limb coordination.
- Dysarthria - slurred and slow speech that is difficult to produce. The patient may also have difficulties controlling volume, rhythm, and pitch.
If the ataxia advances other symptoms may also appear:
- Swallowing difficulties, which may sometimes result in choking or coughing.
- Facial expressions become less apparent.
- Tremors - parts of the body may shake or tremble unintentionally.
- Nystagmus - involuntary rapid rhythmic repetitious eye movement. Movements may be vertical, horizontal, or circular.
- Pes cavus - a foot with too high an arch.
- Cold feet - because of a lack of muscle activity.
- Problems with balance.
- Walking difficulties - in severe cases the patient may need a wheelchair.
- Vision problems.
- Hearing problems.
- Depression - as a result of having to live and cope with the symptoms.
Cerebellar ataxia early onset usually emerges between the ages of 4 and 26. Late onset ataxia generally appears after the patient is 20 years old. Late-onset ataxias usually present less severe symptoms, compared to early-onset ataxia.
Ataxia telangiectasia symptoms generally include:
- Small veins appear around the corner of the eyes, cheeks and ears.
- Physical and sexual development is usually delayed.
Friedreich's ataxia symptoms generally include:
For patients whose symptoms are caused by injury or illness, symptoms often improve over time, and eventually go away completely.
On the next page we look at how ataxia is diagnosed and the available treatments for ataxia.