Annual Incidence and Prevalence
- 0.54 to 0.94 per 100,000 per year in Japan: The annual incidence and prevalence were reported as 0.54 – 0.94 / 100,000 and 6.03 – 10.5 / 100,000, respectively in Japan (2,34).
- 50.7 per 100,000 prevalence in Japan: If asymptomatic patients diagnosed incidentally were included, the prevalence goes up to 50.7 / 100,000 in Japan (20).
- Bimodal distribution with greatest at 5-9 years: There are two peaks, one at the age of 5-9 years and the other smaller one, at the age around (40,48).
- Females more than males: Moyamoya Disease occurs more frequently in females in most populations with the M;F ratio 1:1.6 – 2.18 (2,34,49,61).
- Particularly prevalent in Asians: Although prevalent throughout the world, Moyamoya Disease occurs more frequently in Asians, especially in Far Eastern Asians. In the United States it is reported that African Americans are affected at a higher prevlance than whites or Hispanics (59).
- Family history: Positive family history is a strong risk factor. The incidence in siblings and offspring of probands are about 3% and 2.4%, respectively, 42 and 34 times higher than general population, although this may be lower in North American populations (14,30).
Relationships to Other Disease States and Syndromes
By definition, Moyamoya Disease should not accompany other underlying diseases or conditions. However, there are some conditions that give rise to a quasi Moyamoya Disease state. They are managed in a manner similar to Moyamoya Disease and they may serve as a window to understanding the basic pathophysiology of Moamoya Disease. These conditions include:
- Neurofibromatosis Type I
- Down Syndrome/Trisomy 21
- Sickle cell anemia
- Following cranial irradiation
- Brain tumor
- Systemic arterial narrowing/mid-aortic syndrome with renal artery stenosis