CEREBELLAR LESIONS

CEREBELLAR LESIONS

Cerebellar lesions may be due to tumor, abscess or an injury. Excess alcohol ingestion also leads to cerebellar lesions. Loss of functions of cerebellum also occurs due to degenerative changes in cerebellar cortex, cerebellar nuclei, cerebellar peduncles and spinocerebellar tracts. In general, during cerebellar lesions, there are disturbances in posture, equilibrium and movements. In unilateral lesion, symptoms appear on the affected side because cerebellum controls the same (ipsilateral) side

of the body. Most of the disturbances are due to the damage to corticocerebellum (neocerebellum) because in human beings, it is larger than other divisions.

 DISTURBANCES IN TONE AND POSTURE

1. Atonia or Hypotonia

Atonia is the loss of tone and hypotonia is reduction in tone of the muscle. Cerebellar lesion causes atonia or hypotonia, depending upon the severity of the lesion. Atonia or hypotonia due to cerebellar lesion causes disturbances in the postural reflexes. Cause for atonia or hypotonia during cerebellar

lesion is the loss of facilitatory impulses to gamma motor neurons in the spinal cord via cerebello-vestibulospinal and cerebello-reticulospinal fibers.

2. Attitude

Attitude of the body changes in unilateral lesion of the cerebellum. Changes in the attitude are:

i. Rotation of head towards the opposite side (unaffected side)

ii. Lowering of shoulder on the same side

iii. Abduction of leg on the affected side. Leg is rotated outward.

iv. Weight of the body is thrown on leg of unaffected side. So, trunk is bent with concavity towards

the affected side.

3. Deviation Movement

Deviation movement is the lateral deviation of arms when both the arms are stretched and held in front of

the body, with closed eyes. In bilateral lesion, both the arms deviate and in unilateral lesion, arm of the affected side deviates.

4. Effect on Deep Reflexes

Pendular movements (Chapter 142) occur while eliciting a tendon jerk. These movements are very

common while eliciting the knee jerk or patellar tendon reflex in the patients affected by cerebellar lesion.

A tap on the patellar tendon when leg is hanging freely causes a brisk extension of leg due to the

contraction of quadriceps muscle. In normal conditions, after extension, the leg returns back to resting position immediately. In cerebellar lesion, the leg shows pendular movements.

DISTURBANCES IN EQUILIBRIUM

While Standing

While standing, the legs are spread to provide a broad base and the body sways side-to-side with oscillations of the head.

While Moving – Gait

Gait means manner of walking. In cerebellar lesion, a staggering, reeling and drunken-like gait is observed.

DISTURBANCES IN MOVEMENTS

1. Ataxia: Lack of coordination of movements.

2. Asynergia: Lack of coordination between different groups of muscles such as protagonists, antagonists

and synergists.

3. Asthenia: Weakness, easy fatigability and slowness of muscles.

4. Dysmetria: Inability to check exact strength and duration of muscular contractions required for any

voluntary act. While reaching for an object, the arm may overshoot (past pointing) or it may fall short of

the object. Overshooting is called hypermetria and falling short is known as hypometria.

5. Intention tremor: Tremor that occurs while attempting to do any voluntary act.

6. Astasia: Unsteady voluntary movements.

7. Nystagmus: To and fro movement of eyeball is called nystagmus

8. Rebound phenomenon: When the patient attempts to do a movement against resistance and if the

resis tance is suddenly removed, the limb moves forcibly in the direction in which the attempt was

made. It is called rebound phenomenon. It is due to the absence of breaking action of antagonistic

muscle.

9. Dysarthria: Disturbance in speech. It is due to the incoordination of various muscles and structures

involved in speech.

10. Adiadochokinesis: Ability to do rapid alter nate successive movements such as supination and

pronation of arm is called diadochokinesis. Inability to do rapid alternate successive movements is called

adiadochokinesis. It is a common feature of cerebellar lesion. It is also called dysdiadochokinesia

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