The most important sign of cerebellar disease is ataxia [Greek, a (negative article) + taxi (order)]. Cerebellar ataxia is defined as lack of accuracy or coordination of movement that is not due to paresis, alteration in tone, loss of postural sense, or the presence of involuntary movements. [1 The classic concepts and terminology of asynergia as the cardinal symptom of cerebellar disease were first introduced by Babinski. [2 ,  In the recent literature the term ataxia has come to overturn asynergia/dyssynergia as the broader term, usually being synonymous with incoordination. ^
Cerebellar ataxia relates to motor (dys-)functions of the limbs, trunk, eyes, and bulbar musculature. Ataxia of gait refers to incoordination of walking that might be so severe that the patient cannot walk (abasia). Postural ataxia refers to ataxia of stance and sitting, and includes truncal ataxia. The patient may be unable to sit or stand without support (astasia). Limb ataxia refers to incoordination of limb movements and ataxia of speech to cerebellar dysarthria.
Different terms are commonly used to describe different aspects of ataxia. Dysmetria refers to disturbance of the trajectory or placement of a body part during active movement, both in range and direction. Hypometria refers to a movement undershooting its target, and hypermetria indicates a movement in which the limb overshoots its goal. Bradyteleokinesia describes terminal slowing before reaching the target. Decomposition of movement (asynergia or dyssynergia) refers to errors in the sequence and speed of the component parts of a movement, i.e., a breakdown of a multijoint movement into its constituent parts. Movements previously fluid and accurate become erratic and jerky. Dysdiadochokinesis refers to decomposition of alternating or fine repetitive movements. Deficits appear in the rate of alternation as well as the completeness of the sequence.
Cerebellar disease results in postural and limb tremor. There may be a rhythmic tremor of the body that can evolve into a severe titubation. Limb tremor occurs as a kinetic and, to a lesser extent, static tremor. Kinetic tremor occurs as an oscillatory movement when the subjects initiates a movement of the limb or during the course of moving the limb. The tremor becomes more prominent as the moving limb approaches a target. It has commonly been described as intention tremor, but the term kinetic tremor better describes the clinical appearance. Static tremor develops if the patient attempts to maintain a limb in a fixed position. Usually the position can be sustained steadily for several seconds, but then the limbs develop a rhythmical oscillation generated at the proximal limb muscles.
A variety of eye movement abnormalities are seen in cerebellar disease. Gaze-evoked nystagmus is a common finding. Other frequent abnormalities are impairment of smooth pursuit and saccadic (ocular dysmetria) eye movements, inability to suppress the vestibulo-ocular reflex
(VOR) by fixation, and abnormalities of optokinetic nystagmus.
Hypotonia, hyporeflexia, and asthenia were described as typical symptoms of a cerebellar lesion by Holmes.  They can be seen only in acute lesions. Hypotonia refers to a decrease in the resistance to passive movements of the limbs, associated with pendular tendon reflexes, typified by the lower leg swinging back and forth several times after the knee tendon is tapped with the reflex hammer.
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