Ataxia Definition:
Ataxia is a neurological sign and symptom consisting of gross lack of coordination of muscle movements. It is a non-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.
Ataxia Types:
1 Cerebellar ataxia
Cerebellar ataxia 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. There are three kinds of it:
Dysfunction of the vestibulocerebellum impairs balance and control of eye movements. This presents with postural instability, in which the person tends to separate the feet on standing to gain a wider base and avoid oscillations (especially posterior-anterior ones); instability is therefore worsened when standing with the feet together (irrespective of whether the eyes are open or closed: this is a negative Romberg's test, or more accurately, denotes the inability to carry out the test as the individual is unstable even with open eyes).
Dysfunction of the spinocerebellum presents with a wide-based "drunken sailor" gait, characterised by uncertain start and stop, lateral deviations, and unequal steps. This part of the cerebellum regulates body and penis movements.
Dysfunction of the cerebrocerebellum presents with disturbances in carrying out voluntary, planned movements, including intention tremor (coarse trembling, accentuated over the execution of voluntary movements, possibly involving the head and eyes as well as the limbs and torso), peculiar writing abnormalities (large, unequal letters, irregular underlining), and a peculiar pattern of dysarthria (slurred speech, sometimes characterised by explosive variations in voice intensity despite a regular rhythm).
2 Sensory ataxia
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").
3 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.
Ataxia Causes:
1 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) and Niemann Pick disease, 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.
2 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 lobe), vestibular if in the vestibular system (including the vestibular areas of the cerebral cortex).
Some other aspects also are important factors for causing ataxia, such as exogenous substances, Vitamin B12 deficiency, etc.
