Moyamoya disease is a rare disorder of blood vessels in the brain known as internal carotid arteries (ICA). The condition is characterized by stenosis (narrowing) or occlusion (blockage) of one or both ICA with subsequent formation of an abnormal network of blood vessels adjacent to the ICA.
Moyamoya disease was first described in Japan in 1955. The term moyamoya, a Japanese word that means "puff of smoke," describes the appearance of the abnormal vessels that form adjacent to the internal carotid arteries. Alternate names for the disorder include spontaneous occlusion of the circle of Willis, and basal occlusive disease with telangiectasia.
Moyamoya disease can occur in children (juvenile type) or in adults (adult type). Children tend to be less than age 10 and adults are usually between ages 30 and 49. Affected individuals typically present with signs of stroke or other types of cerebral ischemia (decreased blood flow to an area of the brain due to obstruction in an artery), cerebral hemorrhage (bleeding), or seizures (mainly in children). Symptoms in an affected child or adult may include disturbed consciousness, speech deficits, sensory and cognitive impairment, involuntary movements, or vision problems. Options for treatment for people with moyamoya disease consist of medications and brain surgery. Without treatment, repeated strokes, transient ischemic attacks, brain hemorrhages, or seizures can lead to serious cognitive impairment, physical disability, or death.
Moyamoya disease occurs worldwide and is most prevalent in Asia, and especially in Japan. According to a report in 1998, more than 6000 cases had been described. The disease occurs in about one in a million people per year. Estimates of disease incidence in Japan are as much as ten times greater. Slightly more females than males are affected. The male-to-female ratio has been reported to be around 2:3. Approximately 10% of cases of moyamoya disease are familial.
Causes and symptoms
The cause of moyamoya disease is unknown. Possible explanations for the disorder include injuries to the brain, infection, multifactorial inheritance, genetic factors, or other causes. For example, moyamoya disease has been associated with meningitis, radiation therapy to the skull in children, and genetic conditions such as Down syndrome, neurofibromatosis , and sickle cell anemia. Also, there have been reports linking a region on chromosome 3 (named MYM1) and a region on chromosome 17 (named MYM2) to moyamoya disease in some families.
The initial symptoms of moyamoya disease are somewhat different in children and adults. In children, there is ischemia due to stenosis and occlusion of the circle of Willis, a ring of arteries at the base of the brain. In children, the disease tends to cause repeated "mini-strokes" known as transient ischemic attacks (TIAs) or, less often, seizures. The TIAs usually manifest as weakness of one side of the body (hemiparesis), speech disturbances, and sensory deficits. TIAs may be made worse by hyperventilation, such as with intense crying. Involuntary movements may occur. Mental retardation may be present.
Adults with moyamoya disease typically present with bleeding in the brain (cerebral hemorrhage) or strokes. Cerebral hemorrhage occurs as a result of breakdown of the coexisting blood vessels that formed earlier in life due to stenosis or occlusion of the ICA. The cerebral hemorrhages are commonly located in the thalamus, basal ganglia, or deep white matter of the brain. Symptoms can include disturbance of consciousness and/or hemiparesis. Adult patients with moyamoya disease may go on to have further hemorrhages and strokes which can result in significant and irreversible brain damage.
A diagnosis of moyamoya disease is based on findings from neuroradiologic studies and on clinical signs consistent with this diagnosis. Neuroradiologic studies used to establish the diagnosis of moyamoya disease include cerebral angiography , magnetic resonance imaging (MRI) , magnetic resonance angiography (MRA), and computed tomography (CT ) scan . Cerebral angiography is the most common means of confirming a diagnosis of moyamoya disease. There are reports indicating that MRI and MRA, which are less invasive procedures, may be used instead of cerebral angiography. CT scan findings tend to be non-specific and not as useful as CA, MRI, and MRA in making the diagnosis.
Characteristic brain findings in moyamoya disease include narrowing or occlusion of the end portion of one or both internal carotid arteries, an abnormal network or blood vessels at the base of the brain, and presence of these findings on both sides of the brain. In about 10% of cases, cerebral aneurysms may also be found. Nuclear medicine studies such as Xenon-enhanced CT, positron emission tomography (PET) , or single photon emission computed tomography (SPECT) may be performed in order to evaluate cerebral blood flow (CBF) patterns. The information obtained from CBF studies helps the neurologist and/or neurosurgeon to devise a treatment plan.
There is no cure for moyamoya disease. Early treatment is important to avoid mental and physical impairment. Treatment options include medications and surgical revascularization.
Medications. Individuals having TIAs and stroke may be given antiplatelet drugs, vasodilators, or anticoagulants to help prevent future attacks. Steroid therapy may be prescribed for a person who has involuntary movements. For a patient with a cerebral hemorrhage, treatment may include management of hypertension, if present.
Surgery. The purpose of revascularization surgery in moyamoya disease is to augment or redirect blood flow in the brain. Surgical revascularization has been reported to improve cerebral blood flow, to reduce ischemic attacks, and, in children, to increase IQ. The optimal method of surgery depends on the patient's history and clinical status. There are various direct and indirect methods of restoring blood supply in the brain. Examples of direct bypass surgery include techniques known as superficial temporal artery to middle cerebral artery bypass, and extracranialintracranial bypass to anterior or posterior cerebral artery. Examples of indirect bypass surgery include techniques known as encephaloduroarteriosynangiosis, encephalomyosynangiosis, and encephaloarteriosynangiosis.
Management of moyamoya disease requires a multi-disciplinary approach. In addition to the patient's primary health care professionals, medical professionals involved in the care of patients with moyamoya disease generally include specialists in neurology, neurosurgery, neuroradiology, and anesthesiology. Specialists in orthopedic surgery, ophthalmology, rehabilitation, physical therapy, occupational therapy, speech therapy, and mental health may also be involved in the care of affected individuals. Psychological counseling and contact with other affected patients may assist families in coping with this condition, especially given it's rarity.
Recovery and rehabilitation
The potential for rehabilitation in moyamoya disease depends in part on the degree of impairment caused by complications such as strokes, cerebral hemorrhages, and seizures. Interventions such as physical, occupational, and speech therapy may be recommended for management of problems such as hemiparesis, speech problems, and sensory deficits. Some patients may require assistance with daily living. In cases in which there is significant disability, consideration may be given to in-home nursing care or placement in a residential care facility that can provide 24-hour care and support services.
As of 2004, there were no clinical trials specifically for patients with moyamoya disease. As more is learned about the causes of moyamoya disease, it is hoped that novel therapies may be developed in the future. As of 2004, one laboratory listed on the Gene Tests web site (www.genetests.org) was conducting genetic research on moyamoya disease. Interested patients may discuss the feasibility of participating in this research with their physician.
As of 2004, the prognosis for moyamoya disease was not well defined. The prognosis depends in part on the extent of brain injury present at the time of diagnosis and the success of treatment. For example, a person who had a major stroke or cerebral hemorrhage may already be permanently impaired, both physically and mentally. Reports of clinical outcome after treatment are mixed. Some individuals experience improvement of symptoms while others continue to show progressive decline. Moyamoya disease tends to be more progressive in children than in adults. In those patients who don't stabilize clinically, significant disability or death may occur.
Children with moyamoya disease may have learning disabilities or mental retardation. They may also experience physical disabilities that impact academic performance. Such children may be eligible to have an Individual Education Plan (IEP). An IEP provides a framework from which administrators, teachers, and parents can meet the educational needs of a child with special learning needs. Depending upon severity of symptoms and the degree of learning difficulties, some children with moyamoya disease may be best served by special education classes or a private educational setting.
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The National Institute of Neurological Disorders and Stroke (NINDS). Moyamoya Disease Information Page. <http://www.ninds.nih.gov/health_and_medical/disorders/moyamoya.htm>.
Online Mendelian Inheritance In Man (OMIM). Moyamoya Disease 1. <http://www.ncbi.nlm.nih.gov:80/entrez/dispomim.cgi?id=252350htm>.
Families with Moyamoya Support Network. 4900 McGowan Street SE, Cedar Rapids, IA 52403.
Dawn J. Cardeiro, MS, CGC