cerebellar disorders

Cerebellar disorders have numerous causes, including congenital malformations, hereditary ataxias, and acquired conditions. Symptoms vary with the cause but typically include ataxia (impaired muscle coordination). Diagnosis is clinical and often by imaging and sometimes genetic testing. Treatment is usually supportive unless the cause is acquired and reversible.

The cerebellum has 3 parts:

Archicerebellum (vestibulocerebellum): It includes the flocculonodular lobe, which is located in the medial zone. It helps maintain equilibrium and coordinate eye, head, and neck movements; it is closely interconnected with the vestibular nuclei.

Midline vermis (paleocerebellum): It helps coordinate trunk and leg movements. Vermis lesions result in abnormalities of stance and gait.

Lateral hemispheres (neocerebellum): They control quick and finely coordinated limb movements, predominantly of the arms.

There is growing consensus that, in addition to coordination, the cerebellum controls some aspects of memory, learning, and cognition.

Ataxia is the archetypal sign of cerebellar dysfunction, but many other motor abnormalities may occur (see Table 8: Movement and Cerebellar Disorders: Signs of Cerebellar Disorders).

Table 8

Signs of Cerebellar Disorders

Deficit
Manifestation

Ataxia
Reeling, wide-based gait

Decomposition of movement
Inability to correctly sequence fine, coordinated acts

Dysarthria
Inability to articulate words correctly, with slurring and inappropriate phrasing

Dysdiadochokinesia
Inability to perform rapid alternating movements

Dysmetria
Inability to control range of movement

Hypotonia
Decreased muscle tone

Nystagmus
Involuntary, rapid oscillation of the eyeballs in a horizontal, vertical, or rotary direction, with the fast component maximal toward the side of the cerebellar lesion

Scanning speech
Slow enunciation with a tendency to hesitate at the beginning of a word or syllable

Tremor
Rhythmic, alternating, oscillatory movement of a limb as it approaches a target (intention tremor) or of proximal musculature when fixed posture or weight bearing is attempted (postural tremor)

Etiology

Congenital malformations: Such malformations are almost always sporadic, often occurring as part of complex malformation syndromes (eg, Dandy-Walker malformation—see Congenital Neurologic Anomalies: Etiology) that affect other parts of the CNS. Malformations manifest early in life and are nonprogressive. Manifestations vary markedly depending on the structures involved; ataxia is usually present.

Hereditary ataxias: Hereditary ataxias may be autosomal recessive or autosomal dominant. Autosomal recessive ataxias include Friedreich’s ataxia (the most prevalent), ataxia-telangiectasia, abetalipoproteinemia, ataxia with isolated vitamin E deficiency, and cerebrotendinous xanthomatosis.

Friedreich’s ataxia results from a gene mutation causing abnormal repetition of the DNA sequence GAA in the gene that codes for the mitochondrial protein frataxin. Decreased frataxin levels lead to mitochondrial iron overload and impaired mitochondrial function. Gait unsteadiness begins between ages 5 and 15; it is followed by upper-extremity ataxia, dysarthria, and paresis, particularly of the lower extremities. Mental function often declines. Tremor, if present, is slight. Reflexes and vibration and position senses are lost. Talipes, scoliosis, and progressive cardiomyopathy are common.

Spinocerebellar ataxias (SCAs) are the main autosomal dominant ataxias. Classification of these ataxias has been revised many times recently as knowledge about genetics increases. Currently, at least 28 different gene loci are recognized; at least 10 involve expanded DNA sequence repeats. Some involve a repetition of the DNA sequence CAG that codes for the amino acid glutamine, similar to that in Huntington’s disease. Manifestations vary. Some of the most common SCAs affect multiple areas in the central and peripheral nervous systems; neuropathy, pyramidal signs, and restless leg syndrome, as well as ataxia, are common. Some SCA usually cause only cerebellar ataxia. SCA3, formerly known as Machado-Joseph disease, may be the most common dominantly inherited SCA. Symptoms include ataxia and possibly dystonia, facial twitching, ophthalmoplegia, and peculiar bulging eyes.

Acquired conditions: Acquired ataxias may result from nonhereditary neurodegenerative disorders (eg, multiple system atrophy—see Autonomic Nervous System: Multiple System Atrophy), systemic disorders, or toxin exposure, or they may be idiopathic. Systemic disorders include alcoholism (alcoholic cerebellar degeneration), celiac sprue, hypothyroidism, and vitamin E deficiency. Toxins include carbon monoxide, heavy metals, lithium

,
phenytoin

, and certain solvents.

In children, primary brain tumors (medulloblastoma, cystic astrocytoma) may be the cause; the midline cerebellum is the most common site of such tumors. Rarely, in children, reversible diffuse cerebellar dysfunction follows viral infections.

Diagnosis

Diagnosis is clinical and includes a thorough family history and search for acquired systemic disorders. Neuroimaging, typically MRI, is done. Genetic testing is done if family history is suggestive.

Treatment

Some systemic disorders (eg, hypothyroidism, celiac sprue) and toxin exposure can be treated; occasionally, surgery for structural lesions (tumor, hydrocephalus) is beneficial. However, treatment is usually only supportive.

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