Cerebellar Lesions

The general principle that pertain to most of the disturbances resulting from cerebellar lesions include the following:

• Cerebellar lesions produce ipsilateral disturbances
  
  
• Cerebellar disturbances occur as a constellation of intimately related phenomena
  
  
• Cerebellar disturbances due to non-progressive pathology undergo gradual attenuation with time
  
  
• Disturbances resulting from cerebellar lesions are the physiological expression of intact neural structures deprived of controlling and regulating influences

a) Neocerebellar lesions are the best understood . These lesions affect primarily voluntary and associated movements (i.e. movements related to the corticospinal system). The symptoms/signs include the following:

•  Hypotonia : The tendon reflexes are diminished and the muscles are weak and flabby (asthenia) and also tire easily.

•  Asynergia : Severe disturbances of coordinated movements, in which the range, direction, and force of muscle contractions are inappropriate. Distances are frequently improperly gauged ( dysmetria ) and fall short of the mark or exceed it ( past-pointing ).

(+) Rapid successive movements, such as alternately supinating and pronating the hands and forearms are poorly performed ( dysadiadochokinesia ).

(+) The patient is unable to adjust to changes of muscle tension, so that, for example, when forearms is flexed at the elbow and held flexed against resistance, a sudden release of resistance causes the forearm to strike the chest. This is an example of the rebound phenomenon .

(+) The patients also demonstrate a decomposition of movement , in which phases of complex movements are performed as a series of successive single simple movements.

•  Tremors : These are intention tremors , because they are not present at rest.

•  Ataxia: It results in a bizarre distortion of voluntary and associated movements. It involves particularly the axial muscles, and groups of muscle around the shoulder and pelvic girdles.

•  Nystagmus : This disturbance consists of an oscillatory pattern in which the eyes slowly drift in one direction and then rapidly move in the opposite direction to correct the drift.

•  Speech disturbances : The speech syllables are unnaturally separated. There is slurring of speech, and some words are uttered in an explosive manner.

•  Archicerebellar lesions: These lesions involve mainly portions of the posterior cerebellar vermis (i.e. floculonodular lobe and the uvula, and constitute the archicerebellar syndrome . They produce disturbances of locomotion and equilibrium bilaterally thus:

- The patient is unsteady in standing position and shows considerable swaying of the body.

- On attempting to walk, there is staggering and a tendency to fall to one side or backwards

- The gait is jerky, uncoordinated and resemble that of a drunken individual.

- The muscle tone is not significantly altered, and no tremor or asynergic disturbances are seen in extremities.