Cerebellar ataxia

Genetic factors

Sometimes cerebellar ataxia can have a genetic origin. This is known as autosomal dominant cerebellar ataxia, and results from inherited mutations in the form of triplet repeat expansion, in genes SCA1 to SCA37. Triplet repeat expansion refers to a repeated segment of DNA, known as a trinucleotide repeat, that is unstable and interferes with protein functioning. The mutations are dominant and hence can be transmitted easily. This form of ataxia is registered with the National Organization for Rare Disorders (NORD) and can also be called dentato-rubro-pallido-luysian atrophy and familial progressive cerebellar ataxia.

Alcoholism

One common cause of cerebellar ataxia is alcoholism. When abused for long periods of time, alcohol directly damages the cerebellum, leading to a loss of proper functioning. It also damages subcortical white matter, the connective myelinated fiber tracts of the cerebral cortex, and other parts of the central nervous system. Damage to all of these areas results in ataxia as the systems controlling motor skill become impaired.

Hypothyroidism

Another underlying cause of cerebellar ataxia is hypothyroidism. This occurs when the thyroid gland, at the base of the neck, becomes underactive, producing too little hormone. Thyroid hormones are called triiodothyronine (T3) and thyroxine (T4) which control energy use and metabolism. Too little of them can lead to a lethargy, weight gain, and weakness, amongst other symptoms. The changes in metabolism caused by hypothyroidism lead to cerebellar dysfunction and degeneration. Additionally, hypothyroidism can lead to an increase in antithyroid antibodies, which is thought to lead to cerebellar degeneration.

Infection

Sometimes cerebellar ataxia can result from infection, which causes inflammation in the cerebellum, impairing its ability to function normally. Ataxia is more commonly caused by viral infections like chickenpox, but can be caused by bacterial infections too, such as Lyme disease. This results in a sudden, or acute, attack of ataxia, in a previously healthy patient, and is much more common in children that adults. This kind of cerebellar ataxia is often referred to as acute cerebellar ataxia (ACA), or acute post-infectious ataxia (APCA).

Head trauma and bleeding

Cerebellar ataxia can also be a result of trauma to the head, or bleeding on the brain. Unsurprisingly, head traumas can lead to inflammation of the cerebellum, as well direct damage and injury. This impairs the normal functioning of the cerebellum, leading to cerebellar ataxia. Bleeding into the cerebellum can also cause ataxia.

Tumours

Both cancerous and noncancerous tumours can lead to cerebellar ataxia by affecting the structure of the cerebellum, by placing pressure on it, or causing it to become inflamed.

Cerebral palsy

Cerebral palsy is a condition that affects movement, and is a result of brain injury either before, during, or shortly after birth. If the injury damages the cerebellum, cerebral ataxia can occur. Damage to the cerebellum before, during, and after birth can result from:

• infection in the womb
• loss of oxygen from breaching during birth or placental failure
• head traumas during or after birth
• brain hemorrhages caused by fetal stroke

Idiopathic cerebellar ataxia

Some cerebellar ataxia has no clear cause, and is the result of cerebellar degeneration that has no genetic factor. This type of ataxia is known as idiopathic late onset cerebellar ataxia (ILOCA). Patients with idiopathic cerebellar ataxia show variation in the physical changes in their cerebellum. Some exhibit cerebellar cortical atrophy, which involves degeneration of Purkinje cells in the cerebellar cortex and loss of facultative retrograde cells in the inferior olive (or inferior olivary nucleus). This is the largest nucleus of the olivary body of the medulla oblongata, which inputs to the cerebellum and is important in motor control.

Idiopathic cerebellar ataxia can also result from olivopontocerebellar atrophy, which are transneuronal changes in the cerebellar hemispheres that originate in the olivary and pontine nuclei (in the pons), and result in cerebellar shrinkage. Although sometimes inherited, this form of ataxia often occurs idiopathically with no obvious cause. Ataxia can also result from unexplained changes in the spinal cord, thalamus, cerebral cortex, and basal ganglia of the central nervous system.