What Is Moyamoya Disease?

Moyamoya disease is a rare, treatable vascular condition that affects a little more than one in two million people, worldwide.

Moyamoya disease, also called Moya-moya disease or syndrome, is a cerebrovascular condition, meaning it afflicts the blood vessels of the brain. In those afflicted, a spontaneous narrowing or closing of one or often both carotid arteries results in the production of neovascularity around the base of the brain. Neovascularity is the growth of new, tiny blood vessels surrounding the body of a larger vessel. The fine network of growths appear on an angiogram as a cloud, giving the condition its name, which in Japanese means "misty" or "hazy".

Blockage of the carotid has the effect of cutting off a great deal of circulation to the brain, resulting most commonly in brain damage that can manifest itself as partial or total paralysis, much as in other cases of oxygen deprivation in the brain. The feet, legs, and upper extremities are noted as the most common sites of paralysis. Severe headache, mental retardation, and visual impairment also result, as can psychological problems unrelated to those predating the onset of the disorder. Symptoms vary widely because reduced bloodflow to the brain can affect different parts of the brain differently, depending upon the specifics of the blockage, which artery is blocked (if not both) and other factors that may apply.

Seizures and episodes of ischemia are also reported in cases of Moyamoya. Cases of related ischemia fall under the category of transient cerebral ischemic attacks (TIAs), sometimes called "mini strokes", which involve the temporary and (by comparison) minor blockage of bloodflow to brain tissue. These can result in a temporary shutdown of mental or physical capacity, such as speech irregularity, physical weakness, or sensory hallucination.

Moyamoya is either caused by genetic factors, or by any factor that can cause blockage of the carotid arteries. Genetic cases are called primary Moyamoya syndrome, and account for about one tenth of all cases of the disease. Treatment for genetic Moyamoya usually involves surgery, as the condition responds very little to other forms of treatment. Surgery typically involves bypass of the carotid artery, as attempts to clear blockage are usually impractical and unsuccessful.

Moyamoya occurs most commonly in children and individuals in their thirties or forties, and occurs in about one in two million individuals in the United States, but to some higher degree in Japan; whether this is the result of higher rates of misdiagnosis in other nations or whether this is the result of a genetic predisposition is entirely unclear. Prompt surgical treatment is absolutely necessary once the condition has been diagnosed, as major strokes resulting from the condition can permanently damage a child or adult patient's motor functions, reasoning capacity, and sensation. The long-term outlook for survival is good for patients of all ages, so long as treatment is delivered aptly and quickly, before any serious damage can occur. Non-surgical treatments usually involve symptom management, such as physical therapy to help reduce the effects of minor paralysis. There may be particular doctors who have had experience in dealing with Moyamoya or in other cerebrovascular bypass surgeries. Consult your physician or treatment specialist for more information on finding the best surgeon for you, should you need treatment for the condition.

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