Cerebellar Disorders

Timothy C. Hain, MD

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Last update: 6/26/01. This page is meant to provide a general outline of cerebellar disorders. More specific and detailed material is found in links.

What is the Cerebellum and what does it do ?

The cerebellum is part of the brain. It lies under the cerebrum, towards the back, behind the brainstem and above the brainstem. The cerebellum is largely involved in "coordination". Persons whose cerebellum doesn't work well are generally clumsy and unsteady.

The main clinical features of cerebellar disorders include incoordination, imbalance, and troubles with stabilizing eye movements. There are two distinguishable cerebellar syndromes -- midline and hemispheric.

Midline syndromes are characterized by imbalance. Persons are unsteady, they are unable to stand in Romberg with eyes open or closed, and are unable to well perform tandem gait. Severe midline disturbance causes "trunkal ataxia" a syndrome where a person is unable to sit on their bed without steadying themselves. Some persons have "titubation" or a bobbing motion of the head or trunk. Midline cerebellar disturbances also often affect eye movements. There may be nystagmus, ocular dysmetria and poor pursuit.

Hemispheric cerebellar syndromes are characterized by incoordination of the limbs. There may be decomposition of movement, dysmetria, and rebound. Dysdiadochokinesis is the irregular performance of rapid alternating movements. Intention tremors may be present on an attempt to touch an object. A kinetic tremor may be present in motion. The finger-to-nose and heel-to-knee tests are classic tests of hemispheric cerebellar dysfunction. While reflexes may be depressed initially with hemispheric cerebellar syndromes, this cannot be counted on. Speech may be dysarthric, scanning, or have irregular emphasis on syllables.

The diagnosis of a cerebellar disorder is usually made by a neurologist, and is usually straightforward. MRI scanning often shows shrinkage of part or all of the cerebellum although this is not always the case. Blood tests for specific conditions are now commonly used when there is a family tendency towards these types of symptoms.

Sources of cerebellar injuries

Toxins

There are a large number of processes that injure the cerebellum. Ethanol and many anticonvulsant medications (such as phenytoin and carbamazepine) are cerebellar toxins. Certain types of cancer chemotherapy, such as cytosine arabinoside (Zawacki et al, 2000), are cerebellar toxins. Lithium, given for manic-depressive disorder, is a cerebellar toxin.

Autoantibodies:

The cerebellum may be injured by autibodies such as in the paraneoplastic cerebellar degenerations. These syndromes are accompanied by abnormal blood tests about 50% of the time. The most common tumors are of the lung and breast.

 

Structural lesions (under construction).

Strokes

There are many potential processes that can injure the cerebellum. Strokes are probably the most common. Because the cerebellum is supplied by three major arteries on each side (SCA or superior cerebellar artery, AICA or anterior inferior cerebellar artery, and PICA or posterior inferior cerebellar artery), there are many potential stroke syndromes to consider. The most common syndrome is that if the PICA, also called "Wallenberg's syndrome", or "lateral medullary syndrome". The second most common is the AICA syndrome, and the least frequent is SCA.

Vascular malformations such as cerebellar hemangioblastoma are also fairly common.

Strokes that bleed into the cerebellum, usually hypertensive, can be life threatening and may require surgical decompression.

MS

Multiple sclerosis is another fairly common source of cerebellar disorder. MS often involves the cerebellar connections in the brainstem, and particularly the middle cerebellar peduncle.

Tumors

There are a large number of tumors that can either metastasize to the cerebellum (such as lung or breast cancer), or arise in the cerebellum itself (such as cerebellar astrocytoma or medulloblastoma). The medulloblastoma arises in the cerebellar nodulus, and because of this critical location, often presents with dizziness in addition to hydrocephalus. Patients who have had medulloblastomas surgically removed usually continue to have measurable abnormalities in central vestibular processing (Hain et al, 1988).

Congenital anomalies

Congenital malformations may involve the cerebellum also. The most common is the Arnold-Chiari malformation, which is a condition where the cerebellar tonsils are displaced downward with respect to the skull. Probably second most common are various types of agenesis syndromes. In the Dandy-Walker syndrome (not to be confused with "Dandy's" syndrome, indicating bilateral vestibular loss), there is partial or complete agenesis of the cerebellar vermis, cystic formation of the posterior fossa communicationg with the fourth ventricle, and hydrocephalus. About 80% of the diagnoses of Dandy-Walker are made by the age of 1 year of age. Dandy Walker is often accompanied by other malformations, the most common of which is agenesis of the corpus callosum.

Of the numerous syndromes in which there is vermal agenesis, according to Bordarier and Aicardi (1990), only Goldenhar's syndrome is associated with deafness (pre-auricular tags, mandibular dysostosis, deafness, corneal fibrolipoma).

Inherited cerebellar degenerations:

There are a large number of rare but well described inherited cerebellar disorders. These generally go under the names of Freidreich's ataxia, spinocerebellar atrophy, and olivoponto cerebellar atrophy. See the following link for more information.

Miscellaneous causes:

Recurrent bleeding on the surface of the brain may cause "superficial siderosis", which is typlified by bilateral sensorineural deafness and cerebellar ataxia with dysarthria and nystagmus (Fishman, 1993). These conditions are not covered here in any detail.

 

 

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