When the coordination fails, smoothness of movement is lost and is replaced by:
Strength is preserved. General proprioception is preserved (‘knuckling response’, placing). There may be an ipsilateral menace deficit. Vestibular signs may occur with some cerebellar lesions.
The cerebellum’s main function is to coordinate muscular activity by controlling the rate, range, force and direction of movement of the head, trunk and limbs. Smooth controlled movement results. The cerebellum receives proprioceptive information from muscle, tendon and joints, balance information from the vestibular apparatus, visual information and input from the generators of voluntary motor activity. It regulates motion and muscle tone by influencing the descending motor tracts of the spinal cord.
The kitten was normal when acquired at 8 weeks of age. A male littermate was also bought and this animal had remained normal. Hindlimb ataxia was noted at first vaccination 3 weeks prior to referral and had worsened in the intervening period. The kitten remained ambulatory and could feed.
The kitten was mentally alert and ambulatory with hindlimb ataxia, ‘knuckling-over’ of the right fore, and falling to either side. The head posture was normal except for the fine tremor. Weakness and absent proprioception were found in the hindlimbs. Spinal reflexes were normal.
The lesion was localized to the cerebellum and brainstem or cervical spinal cord. A purely cerebellar lesion could not account for the hindlimb weakness detected on hopping reactions. The proprioceptive deficits of the right forelimb and both hindlimbs could be due to a cervical cord or brainstem lesion. A spinal cord lesion was thought most likely as the mental alertness appeared to be normal. The fine tremor of the head at rest was thought to be due to a cerebellar lesion, although the classic overshooting of an intention tremor was lacking. Myelination defects and CNS inflammation may also cause a tremor.