Excerpt from Moyamoya Disease

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Background

Moyamoya disease is a progressive occlusive disease of the cerebral vasculature with particular involvement of the circle of Willis and the arteries that feed it. Moyamoya (ie, Japanese for "puff of smoke") characterizes the appearance on angiography of abnormal vascular collateral networks that develop adjacent to the stenotic vessels. The steno-occlusive areas are usually bilateral, but unilateral involvement does not exclude the diagnosis.

For related information, see Medscape's Stroke/Cerebrovascular Disease Resource Center.

Pathophysiology

Pathologically, moyamoya disease (MMD) is characterized by intimal thickening in the walls of the terminal portions of the internal carotid vessels bilaterally. The proliferating intima may contain lipid deposits. The anterior, middle, and posterior cerebral arteries that emanate from the circle of Willis may show varying degrees of stenosis or occlusion. This is associated with fibrocellular thickening of the intima, waving of the internal elastic lamina, and thinning of the media. Numerous small vascular channels can be seen around the circle of Willis. These are perforators and anastomotic branches. The pia mater also may have reticular conglomerates of small vessels.

The exact etiology of MMD is unknown. Some genetic predisposition is apparent because it is familial 10% of the time. The disease may be hereditary and multifactorial. A recent Japanese study demonstrated that familial MMD is autosomal dominant with reduced penetrance.

It may occur by itself in a previously healthy individual. However, many disease states have been reported in association with MMD, including the following:

• Immunological - Graves disease/thyrotoxicosis
• Infections - Leptospirosis and tuberculosis
• Hematologic disorders - Aplastic anemia, Fanconi anemia, sickle cell anemia, and lupus anticoagulant
• Congenital syndromes - Apert syndrome, Down syndrome, Marfan syndrome, tuberous sclerosis, Turner syndrome, von Recklinghausen disease, and Hirschsprung disease
• Vascular diseases - Atherosclerotic disease, coarctation of the aorta and fibromuscular dysplasia, cranial trauma, radiation injury, parasellar tumors, and hypertension

These associations may not necessarily be causative, but do warrant consideration due to impact on treatment.

Frequency

United States

The incidence of moyamoya disease is highest in Japan (see International). However, a recent study indicated that the prevalence of MMD in California and Washington was 0.086 case per 100,000 population. In this study, the breakdown based on ethnicity as ratio to whites was 4.6 for Asian Americans, 2.2 for African Americans, and 0.5 for Hispanics.

International

The prevalence and incidence of moyamoya disease in Japan has been reported to be 3.16 cases and 0.35 case per 100,000 people, respectively. With regard to sex, the female-to-male ratio is 1.8:1. A bimodal peak of incidence is noted, with symptoms occurring either in the first decade or in the third and fourth decades of life.

Mortality/Morbidity

Mortality rates of moyamoya disease are approximately 10% in adults and 4.3% in children. Death is usually from hemorrhage. About 50-60% of affected individuals experience a gradual deterioration of cognitive function, presumably from recurrent strokes.

Race

Moyamoya disease occurs primarily in Asians, but it also can occur (with varying degrees of severity) in whites, African Americans, Haitians, and Hispanics.

Sex

The female-to-male ratio of moyamoya disease is 1.8:1.

Age

Ages range from 6 months to 67 years, with the highest peak in the first decade and smaller peaks in the third and fourth decades.

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