The Common Vein Copyright 2010
Ataxia is a syndrome in which there is a defect of motor coordination not caused by a deficiency of the musculoskeletal system, which, in the absence of apraxia, there is a change in the amplitude and direction of the voluntary movements, posture and balance.
It results from a disorder in the cerebellum or from the systems that relay input to it – the proprioceptive sensitivity and the vestibular system. As such, 3 different types of ataxia are described: sensitive, cerebellous and vestibular.
Focusing on the cerebellum, vestibulocerebellar lesions cause primarly disturbances in the balance, and hence an ataxic gait. Lesions of the vermis cause a more central gait ataxia with relative sparing of the limbs. Neocerebellar lesions, that is, cerebellar hemispheres, produce conversely appendicular ataxia. Besides imbalance and gait changes, intention tremor, dysarthria and ocular movement disturbances also occur, mainly because all of these require fine motor control, which is then absent.
Neurological examination also determines whether the ataxia is primarily cerebellar, primarily sensory, or a combination of both. Further diagnostic considerations and avenues for investigation are aimed at making a specific diagnosis
Paraneoplastic and demyelinating cases account for the majority of subacute cases. Hereditary forms constitute the principal differential diagnoses in the chronic and slowly progressive presentations. Infarction, tumor and demyelinating disease are other major causes, when they affect either the cerebellum or its connections.
Neuroradiology is helpful through both CT and MRI in terms of suggesting the likely etiology of the syndrome, by demonstrating posterior fossa tumors/malformations, stroke/degenerative disorders in the cerebellum, MS or pathologic changes outside the cerebellum that would likely cause a disruption of the afferent/efferent systems, including the vestibulum and the accoustic nerve.