Olivopontocerebellar atrophy (OPCA) is a group of disorders characterized by degeneration of three brain areas: the inferior olives, the pons, and the cerebellum. OPCA causes increasingly severe ataxia (loss of coordination) as well as other symptoms.
Two distinct groups of diseases are called OPCA, leading to some confusion. Non-inherited OPCA, also called sporadic OPCA, is now considered a form of multiple system atrophy (MSA). Hereditary OPCA, also called inherited OPCA and familial OPCA, is caused by inheritance of a defective gene, which is recognized in some forms but not in others.
Hereditary OPCA affects approximately 10,000 people in the United States, with males affected approximately twice as often as females. The average age of onset is 28 years.
Causes and symptoms
By definition, hereditary OPCA is caused by the inheritance of a defective gene. Several genes have been identified. The two most common are known as SCA-1 and SCA-2 (SCA stands for spinocerebellar ataxia). These genes cause similar, though not identical, diseases. Besides these two genes, there are at least 20 other genetic forms of the disease. For reasons that are not understood, these gene defects cause degeneration (cell death) in specific parts of the brain, leading to the symptoms of the disorder. The cerebellum is a principal center for coordination, and its degeneration leads to loss of coordination.
The most common early symptom of OPCA is ataxia, or incoordination, which may be observed in an unsteady gait or over-reaching for an object with the hand. Other common symptoms include dysarthria (speech difficulty), dysphagia (swallowing difficulty), nystagmus (eye tremor), and abnormal movements such as jerking, twisting, or writhing. Symptoms worsen over time.
An initial diagnosis of OPCA can be made with a careful neurological examination (testing of reflexes, balance, coordination, etc.), plus a magnetic resonance image (MRI) of the brain to look for atrophy (loss of tissue) in the characteristic brain regions. Genetic tests exist for SCA-1 and SCA-2 forms. Many other types of tests are possible, although they are usually done only to rule out other conditions with similar symptoms or to confirm the diagnosis in uncertain cases. Because the symptoms of OPCA can be so variable, especially at the beginning of the disease, it may be difficult to obtain a definite diagnosis early on.
There are no treatments that reverse or delay the progression of OPCA.
Very few medications have any beneficial effect on OPCA symptoms. In some patients, Levodopa, also prescribed for Parkinson's disease, may initially help. Some anti-tremor medications, including propranolol, may also slightly help. Acetazolamide may be useful in some forms of the disease.
Treatment of OPCA is primarily directed toward reducing the danger of ataxia, and minimizing the impact of the disease on activities of daily living. Falling is the major danger early in the disease, and assistive mobile devices such as walkers and wheelchairs are often essential to prevent falling.
As the disease progresses, swallowing difficulties present the greatest danger. Softer foods and smaller mouthfuls are recommended. A speech-language pathologist can help devise swallowing strategies to lessen the risk of choking, and can offer advice on assisted communication as well. Late in the disease, a feeding tube may be needed to maintain adequate nutrition.
The life expectancy after diagnosis is approximately 15 years, although this is an average and cannot be used to predict the lifespan of any individual person.
Because OPCA is an inherited disease with identified genetic causes, it is reasonable to have other family members tested for the genes to determine if they, too, are at risk. This information may help family members to make personal decisions about their future, including decisions about family planning.
National Ataxia Foundation. (April 19, 2004). <http://www.ataxia.org>.
National Organization for Rare Disorders. (April 19, 2004). <http://www.rarediseases.org>