Moyamoya Disease

Moyamoya disease is a rare cause of stroke characterized by the progressive narrowing of the main arteries supplying the anterior part of the brain, including the internal carotid arteries and their branches. 

The exact cause of moyamoya disease is currently unknown; however, recent evidence suggests there may be a genetic predisposition. There have been several mutations associated with the disease, specifically the RNF213 and ACTA2 genes. These mutations appear to affect the development and growth of smooth muscle cells in the walls of affected arteries. How this process leads to the classic findings of moyamoya disease is still not understood.

Moyamoya disease is more common in individuals assigned female at birth and has a bimodal distribution with two peaks of incidence: one in children and another in adults around 40 years old. Although moyamoya cases have been reported all over the world, it is more common in East Asian populations, especially in Korea, Japan, and China. A similar elevation in prevalence has been reported among people of Asian descent living in Western countries, which suggests there may be specific genetic factors that contribute to moyamoya disease in those populations.

The most common clinical presentation of moyamoya disease is an ischemic stroke, which occurs when blood flow to the brain is reduced due to a blocked artery. Symptoms of stroke depend on the areas of the brain affected and may include sudden muscle weakness or paralysis, numbness, slurred speech or difficulty understanding speech, and cognitive impairment. Some individuals may also experience transient ischemic attacks (TIAs), which are episodes of transient neurologic dysfunction caused by a brief disruption in cerebral blood flow that lasts a few minutes or hours. Given their low blood supply reserve, individuals with moyamoya have minimal tolerance for any physiologic stress. Therefore, ischemic events can often be triggered by common situations, such as dehydration, blood pressure changes, and excessive crying or straining in children. 

In addition to surgery, supportive measures include medications to reduce the risk of having future strokes. For example, antiplatelet agents like aspirin can help prevent the formation of blood clots within the cerebral circulation. Additionally, calcium-channel blockers like nicardipine may be given to help treat severe headaches and reduce the risk of transient ischemic attacks in selected individuals.