Ataxia

SOURCE: www.MedlinePlus.gov and www.Wikipedia.org

Ataxia is a neurological sign and symptom consisting of gross incoordination of muscle control or an inability to finely coordinate movements, resulting in a jerky, unsteady, to-and-fro motion of the trunk or the limbs. Ataxia is an specific clinical manifestation implying dysfunction of parts of the nervous system that coordinate movement, such as the cerebellum. Several possible causes exist for these patterns of neurological dysfunction.  Uncoordinated movement is an abnormality of muscle control or an inability to finely coordinate movements, resulting in a jerky, unsteady, to-and-fro motion of the trunk or the limbs.

Types of ataxia

Cerebellar ataxia

The term cerebellar ataxia is employed to indicate ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits, such as antagonist hypotonia, asynergy, dysmetria, dyschronometria, and dysdiadochokinesia. How and where these abnormalities manifest depend on which cerebellar structures are lesioned, and whether the lesion is bilateral or unilateral.

Sensory ataxia

The term sensory ataxia is employed to indicate ataxia due to loss of proprioception (sensitivity to joint and body part position), which generally depends on dysfunction of the dorsal columns of the spinal cord, since they carry proprioceptive information up to the brain; in some cases, the cause may instead be dysfunction of the various brain parts that receive that information, including the cerebellum, thalamus, and parietal lobes. Sensory ataxia presents with an unsteady "stomping" gait with heavy heel strikes, as well as postural instability that is characteristically worsened when the lack of proprioceptive input cannot be compensated by visual input, such as in poorly lit environments. Doctors can evidence this during physical examination by having the patient stand with his / her feet together and eyes shut, which will cause the patient's instability to markedly worsen, producing wide oscillations and possibly a fall (this is called a positive Romberg's test). Worsening of the finger-pointing test with the eyes closed is another feature of sensory ataxia. Also, when the patient is standing with arms and hands extended toward the examiner, if the eyes are closed, the patient's finger will tend to "fall down" and be restored to the horizontal extended position by sudden extensor contractions ("ataxic hand").

Vestibular ataxia

The term vestibular ataxia is employed to indicate ataxia due to dysfunction of the vestibular system, which in acute and unilateral cases is associated with prominent vertigo, nausea and vomiting. In slow-onset, chronic bilateral cases of vestibular dysfunction, these characteristic manifestations may be absent, and dysequilibrium may be the sole presentation.

Causes of ataxia

The three types of ataxia have overlapping causes, and can therefore either coexist or occur in isolation.

Focal lesions

Any type of focal lesion of the central nervous system (such as stroke, brain tumour, multiple sclerosis will cause the type of ataxia corresponding to the site of the lesion: cerebellar if in the cerebellum, sensory if in the dorsal spinal cord (and rarely in the thalamus or parietal lobes), vestibular if in the vestibular system (including the vestibular areas of the cerebral cortex).

Exogenous substances

Exogenous substances that cause ataxia mainly do so because they have a depressant effect on central nervous system function. The most common example is ethanol, which is capable of causing overlapping cerebellar and vestibular ataxia. Other examples include both prescription drugs (e.g. most antiepileptic drugs have cerebellar ataxia as a possible unwanted effect) and recreational drugs (e.g. ketamine, PCP).

Vitamin B₁₂ deficiency

Vitamin B₁₂ deficiency may cause, among several neurological abnormalities, overlapping cerebellar and sensory ataxia.

Causes of isolated sensory ataxia

peripheral neuropathies may cause generalized or localized sensory ataxia (e.g. a limb only) depending on the extent of the neuropathic involvement. Spinal disorders of various types may cause sensory ataxia from the lesioned level below, when they involve the dorsal columns.

Non-hereditary cerebellar degeneration

Non-hereditary causes of cerebellar degeneration include chronic ethanol abuse, paraneoplastic cerebellar degeneration, high altitude cerebral oedema, coeliac disease, and normal pressure hydrocephalus.

Hereditary ataxias

Ataxia may depend on hereditary disorders consisting of degeneration of the cerebellum and/or of the spine; most cases feature both to some extent, and therefore present with overlapping cerebellar and sensory ataxia, even though one is often more evident than the other. Hereditary disorders causing ataxia include autosomal dominant ones such as spinocerebellar ataxia, episodic ataxia, and dentatorubropallidoluysian atrophy, as well as autosomal recessive disorders such as Friedreich's ataxia (sensory and cerebellar, with the former predominating), ataxia-telangiectasia (sensory and cerebellar, with the latter predominating), and abetalipoproteinaemia. An example of X-linked ataxic condition is the rare fragile X-associated tremor/ataxia syndrome.