The close relationship of structures within the posterior fossa makes the identification of exclusively cerebellar symptoms and signs difficult. Disease of the brain stem and its connections may produce identical results.
- vermis (and flocculonodular lobe) Results in: disturbance of equilibrium with unsteadiness on standing, walking and even sitting (truncal ataxia). The patient's gait is broad based and reeling. Eye closure does not affect balance (see Romberg's test). Tests of vestibular function, e.g. calorics, may be impaired.
Damage to hemisphere structures
- always produces signs ipsilateral to the side of the lesion.
Results in: a loss of the normal capacity to modulate fine voluntary movements. Errors or inaccuracies cannot be corrected. The patient complains of impaired limb co-ordination and certain signs are recognised:
Ataxia of extremities with unsteadiness of gait towards the side of the lesion. Dysmetria: a breakdown of movement with the patient 'overshooting' the target when performing a specific motor task, e.g. finger-to-nose test. Dysdiadochokinesia: a failure to perform a rapid alternating movement. Intention tremor: a tremor which increases as the limb approaches its target.
Rebound phenomenon: the outstretched arm swings excessively when displaced.
'Pendular' reflexes: the leg swings backwards and forwards when the knee jerk is elicited.
Nystagmus results from disease affecting cerebellar connections to the vestibular nuclei.
In unilateral disease, amplitude and rate increase when looking towards the diseased side.
Other ocular signs may occur, e.g. ocular dysmetria - an 'overshoot' when the eyes voluntarily fixate.
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