Cerebellar degeneration

Gross landmarks

The surface of the cerebellum is marked by a series of small infoldings called folia. It consists of two hemispheres separated by a vermis. Both hemispheres are divided into longitudinal and transverse zones by five deep fissures. The primary fissure divides the body of the cerebellum into anterior and posterior lobes. This fissure is easily observed on midsagittal sections of the cerebellum.

The posterolateral fissure separates the body of the cerebellum from the flocculonodular lobe. The other three fissures are posterior superior, horizontal and pre-pyramidal fissures and form the basis of subdivisions.

A dural infolding called the tentorium cerebelli separates the superior surface of the cerebellum from the inferior surface of the occipital lobe. Three peduncles connect the cerebellum to other neural structures.

The superior cerebellar peduncle connects the cerebellum to the midbrain. It contains mainly efferent fibers from the intracerebellar nuclei and also some afferent fibers like the anterior spinocerebellar tract. The middle cerebellar peduncle is the largest of the three. It arises from the posterolateral surface of the pons and carries fibers from contralateral pontine nuclei. The inferior cerebellar peduncle connects the medulla oblongata and cerebellum. It primarily contains afferents fibers along with some efferents.   

Functional divisions

In general, the cerebellum is responsible for coordinating voluntary muscle movements and controlling equilibrium. Specific functions of the deep cerebellar nuclei divide it into three functional divisions.

The spinocerebellum is in the paravermal region, or just lateral to the vermis, contains the interposed nuclei. This zone coordinates limb and trunk movements.

The pontocerebellum, or neocerebellum, in the lateral hemispheres contains the dentate nuclei. It is the largest part of cerebellum and newest from an evolutionary point of view. This zone is involved in planning the timing of limb movements and coordination of speech.

The vestibulocerebellum is the most medial zone. It is made up of the vermis and flocculonodular lobe and contains the fastigial nuclei. This zone is responsible for coordinating eye movements and balance.  

Blood supply

Several arteries provide the blood supply to the cerebellum:

• superior cerebellar artery
• anterior inferior cerebellar artery
• posterior inferior cerebellar artery

The superior cerebellar artery arises from the basilar artery near the Circle of Willis. It divides into many branches at the superior surface of the cerebellum and supplies this region. The anterior inferior cerebellar artery arises from the basilar artery near the foramen magnum. It supplies the inferior cerebellar surface and anastomoses with the posterior inferior cerebellar artery. The posterior inferior cerebellar artery arises from the vertebral artery near the lower end of the olive. Between the hemispheres, it divides into lateral and medial branches to supply the different parts of cerebellum.

Symptoms and signs

This condition refers to the deterioration of the neurons mostly affecting the Purkinje cell layer in the cerebellum, which leads to cerebellar atrophy and dysfunction. Cerebellar nuclei are also affected in some cases. The degenerative cerebellar disorders are slowly progressive disorders. Other areas of the central nervous system including the spinal cord, medulla oblongata, cerebral cortex, and brainstem can be involved in this degenerative disorder.

Overall, cerebellar degeneration presents with decreased muscle tone and loss of coordination in both skeletal and smooth muscle tissue. The group of disorders associated with progressive degeneration of cerebellum is Degenerative cerebellar ataxia. In general there is wide legged and unsteady walk with tremors in the trunk of the body and jerky movements of the arms or legs. Patients may also exhibit slow and slurred speech; nystagmus is also a feature commonly seen. More specific symptoms reflect the region of the cerebellum that is degenerating.

• Spinocerebellum
  • Truncal ataxia
  • “drunken” gait
• Neocerebellum
  • Ataxia of limbs
  • Jerky voluntary muscle movements
  • Loss of coordination
  • Dysmetria - difficulty judging distance, may overshoot objects when reaching
  • Dysdiadochokinesia - inability to perform rapidly changing actions, for example turning a door handle
  • Rebound phenomena
  • Intention tremor
• Vestibulocerebellum
  • Equilibrium is affected
  • Nystagmus - involuntary eye movements

First group: Acquired ataxia (non-hereditary ataxia)

Resulting due to

• Autoimmune disorders
• Ischemic or hemorrhagic stroke
• Chronic alcohol abuse
• Poor diet
• Vitamin B12 or Vitamin E deficiency
• Multiple sclerosis
• Some sedatives
• Creutzfeldt-Jakob (Prion) Disease
• Tumors, especially lung, gynecological, and breast cancer

Second group: Hereditary ataxia

• Autosomal-dominant (Spinocerebellar ataxia)
• Autosomal-recessive (Friedreich’s ataxia)
• X-linked
• Mitochondrial transmission

Although tumors or genetic disorders cause degeneration throughout the cerebellum, some conditions result in degeneration of specific regions. For example, hemorrhages tend to affect the cerebellar hemispheres more than midline structures. Alcohol misuse however tends to affect the vermis.

Tests for limb ataxia

Finger to nose test

In the Finger to Nose Test a clinician asks the patient to touch his or her nose and then the clinician’s finger. This action is repeated several times. A healthy individual will be able to reach the finger and nose in a smooth path. An individual with cerebellar damage may show appendicular ataxia. In this instance the patient can not make a direct path between the finger and nose. His or her hand may divert off course several times and may miss the target completely. Appendicular ataxia specifically indicates damage to the intermediate and lateral portions of the ipsilateral cerebellum.

Heel-shin test

In this test, the patient is asked to rub his or her heel up and down along their contralateral shin. A healthy patient will be able to do this in a straight line. A patient with cerebellar damage will show a wobbly, uncontrolled path. This is another indication of appendicular ataxia.

Tests for truncal ataxia

Truncal ataxia presents as an unsteady gait. This can be demonstrated by asking the patient to walk a short distance in a tandem gait. To walk in a tandem gait the patient steps in a heel-to-toe pattern. Patients with truncal ataxia will deviate to one side and may even fall over. Another method of testing this of the Romberg test. In the Romberg test the patent is asked to close their eyes and stand with their feet close together. Swaying and even toppling over indicates cerebellar damage.

Genetic testing

Genetic testing is available for cerebellar degeneration caused by inheritance or genetic change.

Neuroimaging

A brain MRI or CT scan can indicate damage to the cerebellum or the presence of a tumor. A patient whose degeneration is the result of a stroke will show an infarction in the location supplied by the damaged artery. In this case neuroimaging can indicate both the presence of degeneration and determine which artery is damaged.