Makindo Medical Notes

Cerebellar signs may not just be due to cerebellar disease but also its connections to the brain, vestibular system and spine. The cerebellum is organized into several key structures that work together to process and coordinate motor and cognitive functions.

Cerebellar Cortex

• The cerebellar cortex is the outer layer of the cerebellum, consisting of three distinct layers:
• Molecular Layer: The outermost layer, containing a network of connections between neurons but relatively few cell bodies.
• Purkinje Cell Layer: The middle layer, containing large Purkinje cells that serve as the primary output neurons of the cerebellar cortex.
• Granular Layer: The innermost layer, packed with small granule cells that receive input from various sources and relay information to the Purkinje cells.

Deep Cerebellar Nuclei

Located within the cerebellum’s white matter, the deep cerebellar nuclei are clusters of neurons that act as the primary output centers for the cerebellum. They receive inhibitory input from the Purkinje cells and excitatory input from other parts of the brain and spinal cord, and they send processed information to various motor and cognitive regions of the brain.

Cerebellar Peduncles

• Superior Cerebellar Peduncle: Carries output from the cerebellum to the midbrain and thalamus, influencing motor control.
• Middle Cerebellar Peduncle: The largest peduncle, conveying input from the cerebral cortex to the cerebellum, primarily via the pontine nuclei.
• Inferior Cerebellar Peduncle: Transmits sensory information from the spinal cord and brainstem to the cerebellum, as well as output to the vestibular nuclei.

Function and Mechanism

Coordination of Movement

The cerebellum receives input from the motor cortex, sensory systems, and other parts of the brain. It integrates this information to fine-tune and coordinate muscle movements, ensuring that movements are smooth, precise, and appropriately timed.

Balance and Posture

Motor Learning

The cerebellum is involved in motor learning, which is the process of improving motor skills through practice. For example, when learning to play a musical instrument or ride a bicycle, the cerebellum helps the body learn and refine these complex motor tasks by adjusting the strength and timing of motor commands based on feedback from previous attempts.

Non-Motor Functions

Output and Feedback

The cerebellum sends its output to various regions of the brain via the deep cerebellar nuclei. This output influences the motor cortex and other brain areas to adjust ongoing movements and prepare for upcoming actions. The cerebellum continuously receives feedback about the success of movements and makes necessary adjustments to improve accuracy and coordination.

Clinical

• Damage to the vestibulocerebellum can manifest with loss of balance, abnormal gait with a wide stance.
• Signs of Cerebellar disease are ipsilateral to the lesion
• Dysdiadochokinesia - unable to do rapidly alternating movements
• Past pointing / dysmetria
• Broad based ataxic gait - Truncal with midline lesion, limb ataxia
• Coarse Nystagmus to the affected side - horizontal and ipsilateral.
• Intention tremor - finger-nose test and lower limb equivalent the heel shin test
• Hypotonia and inability to learn new movements
• Pendular reflexes, Wide broad-based gait
• Riddoch's sign - elevation and over-pronation of the outstretched hand
• Scanning dysarthria - monotone slurred staccato speech and scanning

Symmetry

• Unilateral cerebellar disease: MS, Stroke
• Bilateral signs: alcohol, drugs, inherited or multiple foci of demyelination or strokes
• Truncal ataxia and/or gait ataxia without limb coordination indicates a midline (vermis) lesion

Causes

• Stroke disease - infarcts and bleeds PICA, AICA, superior cerebellar artery
• Multiple Sclerosis and other causes of demyelination
• Primary Neoplasia - Posterior fossa tumour in children, cerebellopontine angle tumour in adults
• Secondary neoplasia - Lung, breast, bowel
• Paraneoplastic - small cell lung cancer anti-Purkinje cells =anti-Yo
• Hereditary - Friedreich's ataxia (AR) Spinocerebellar ataxia 1-14 (AD)
• Developmental - Arnold-Chiari malformation or Dandy-Walker malformation
• Inherited - Ataxia-telangiectasia, Refsum's disease, progressive myoclonic epilepsy
• Drugs - Anticonvulsants, alcohol
• Infection - Varicella zoster, EB, HIV, Mycoplasma, Legionella
• Carbon monoxide poisoning
• Prion disease - Gerstmann-Straussler-Schenker syndrome
• Multiple systems atrophy - Cerebellar variant
• Hodgkin-Ab - cerebellar degeneration in those with Hodgkin's lymphoma