lunes, 17 de septiembre de 2018

What is Spinocerebellar Ataxia?

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By Lois Zoppi, BAReviewed by Akshima Sahi, BDS

Ataxia is a degenerative disease affecting the nervous system, presenting poor coordination and movement, difficulties with speech, walking, fine motor skills, swallowing, and vision. It mainly affects people over 18 (adult-onset).

Spinocerebellar ataxia (SCA) is a form of hereditary, progressive ataxia with more than 20 identified types sharing similar symptoms. There is currently no treatment or cure to slow the progression of spinocerebellar ataxia.

Causes of Ataxia

Damage to the cerebellum, the part of the brain that is responsible for coordinating movement, is usually the cause of ataxia. However, damage to parts of the nervous system can also cause ataxia. This damage can be due to injury or trauma, lack of oxygen to the brain, excessive alcohol consumption over a long period of time, or an existing condition such as multiple sclerosis (MS). Ataxia can also be hereditary, caused by a faulty gene passed on by family members who don’t always show signs of ataxia themselves.

Types of Ataxia

There are three main categories of ataxia:

Acquired (non-genetic) ataxia

Acquired ataxia is generally caused by environmental factors like injury, tumour or chemical exposure, and can affect anyone of any age and develops quickly over hours or days. It can both worsen or improve over time or stay the same.

Hereditary ataxia

Friedrich’s ataxia is the most common form of hereditary ataxia, affecting around one in 50,000 people with symptoms starting during childhood or teenage years. People with Friedrich’s ataxia generally have a shorter life expectancy than normal as it has damaging effects on heart.

Idiopathic late-onset cerebellar ataxia (ILOCA)

ILOCA starts at around age 50 and symptoms worsen slowly over time.

Spinocerebellar Ataxia

Spinocerebellar ataxia is a hereditary form of ataxia affecting people from age 25 to 80, and is characterized by:

Problems with balance and coordination
Dysarthria (slurred and slow speech)
Dysphagia (difficulty swallowing)
Cramps and muscle stiffness
Peripheral neuropathy (loss of feeling in hands and feet)
Memory loss
Slow eye movement
Incontinence (reduced bladder control)

Depending on the type of SCA, different symptoms may be present.

Causes of Spinocerebellar Ataxia

The cause of spinocerebellar ataxia is atrophy of the cerebellum, as seen in other forms of ataxia. Onset of spinocerebellar ataxia is generally after the age of 18 and progresses slowly, with symptoms worsening over a period of years. Some types of SCA can progress more quickly.

SCA can be inherited in an autosomal dominant fashion. Symptoms can become present from just one mutated copy of the responsible gene in each cell, but some cases are caused by trinucleotide repeat expansions, where a section of DNA is repeated many times. These repeats do not always cause problems. Often, the higher the number of repeats, the earlier the onset and worse the symptoms will be.

Symptoms of Spinocerebellar Ataxia

Clinical features different to the other forms of ataxia include several non-cerebellar features, including:

Parkinsonism
Chorea (involuntary movement disorder)
Cognitive impairment
Peripheral neuropathy
Seizures

Diagnosis

Ataxia is diagnosed through methods including medical history, family history, blood tests to rule out other conditions presenting similar symptoms, and neurological evaluations. 12 types of ataxia, Friedrich’s ataxia and a number of others have genetic blood tests to aid diagnosis; however, some forms of SCA cannot be precisely diagnosed as they have not been genetically identified. In spinocerebellar ataxia, this makes up about 25% to 40% of cases. As there is an overlap in symptoms between the different types of spinocerebellar ataxia, genetic testing can be used to concretely diagnose the type of SCA affecting a patient. In these cases, neurological examinations that may include MRI scans of the brain and spine may be used to diagnose SCA.

Treatment

There is currently no treatment or cure to slow or stop the progression of SCA or the damage to the cerebellum. Patients work closely with a neurologist to develop a personal plan to deal with the symptoms of ataxia, which can include speech therapy, occupational therapy, and physical therapy. Medication can be given in conjunction with therapy to help symptom management.

Prognosis of Spinocerebellar Ataxia

The prognosis for people with spinocerebellar ataxia is variable, and is different depending on the type of SCA. Prognosis is often based on the most common types of SCA, SCA1, SCA2, SCA3 and SCA6. Those with these types of SCA will normally need a wheelchair 10-15 years after symptoms arise, and help with daily tasks will be needed.