Characteristics of Moyamoya Disease
Moyamoya disease is an arterial disorder. Specifically, it’s a disorder of angiogenesis – of the formation of blood vessels. It affects the internal carotid arteries that carry blood to the brain.
Anatomically, the carotid arteries are the two vessels closest to the heart. They run upward through the neck, where each one divides into two: internal carotid arteries and external carotid arteries.
From the neck, each pair of vessels enters the skull carrying the blood pumped by the heart to the brain. Thus, any problem in these vessels is potentially lethal.
In moyamoya disease, the internal carotid arteries become narrowed, decreasing the blood flow to the brain. Since one of the priorities of the human body is to ensure proper brain circulation, it develops a network of small blood vessels to bypass any obstruction.
These new, neovascular vessels generate an accessory pathway for blood to flow from the heart. Furthermore, the small collateral vessels located at the base of the skull, when viewed through complementary diagnostic methods, emulate cigarette smoke floating in the air.
Moya-moya means “cloud of smoke” in Japanese, hence the etymology of the name of this disease. It’s also the word that describes the smoke coming out of volcanoes. Scientists Suzuki and Takaku gave the name to this disease in 1969 after looking at some angiographic images of it.
Distribution of moyamoya disease
Moyamoya disease has an age distribution in two peaks. Generally, symptoms are present in children and middle-aged adults. However, the group most affected is the one with infants between five and ten years of age. The second group is made up of people between thirty and fifty years old.
The most affected area is Southeast Asia, although there are cases worldwide. The countries of Japan, China, and Korea have the largest number of global cases. For example, the prevalence in Japan is one in every thirty-two thousand inhabitants.
Also, a series of studies conducted in Southeast Asia discovered that for every two thousand Japanese adults without symptoms of the pathology, there’s one who’s brain images are compatible with moyamoya disease.
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The etiology of the disease isn’t clear yet. However, we suspect it’s genetic and that the arterial obstruction has a hereditary component.
In any case, there are five risk factors that increase a person’s predisposition to it:
- Family history. The probability that a direct relative will also have moyamoya disease increases by up to forty times when a family member has had it.
- Asian ancestry. The association may occur due to genetic issues. People who are born or come from Southeast Asia are much more likely to have the disorder than people in the rest of the world.
- Females. The disease is more frequent among women.
- Children under 15 years of age. This is one of the most affected age groups, as mentioned above.
- Other diseases. Some cases of moyamoya happened in combination with certain pathologies — Down’s Syndrome, for example.
Symptoms of moyamoya disease
It usually begins with a stroke. Either because the arterial blockage doesn’t allow enough blood flow to the brain, or because the accessory vessels are weak and break under stress — both ischemia and hemorrhage can be lethal.
Strokes often provide early warnings. In children, repeated seizures often occur in response to a lack of brain circulation. In adults, there may be transient ischemia expressed as hemiparesis or hemiplegia.
These are some of the symptoms of poor brain circulation:
- Visual alterations
- Speech difficulties
- Involuntary movements
Crying is a common trigger in children, especially when they hyperventilate by doing so intensely. Hyperventilation requires a change in the blood flow to the brain that’s regulated through the constriction and dilation of the blood vessels and can lead to rupture.
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Diagnosis and treatment
The only way to diagnose moyamoya is via brain imaging. Angiography and angioresonance are the main studies with which to detect this kind of illness. This is because any decrease in arterial light in the internal carotids will be visible in the images obtained through them.
Finally, the treatment is:
- Firstly, pharmacological. Medications don’t reverse the evolution but contribute to reducing the risk of stroke. People have used anticoagulants, vasodilators, and antiplatelet agents.
- Secondly, surgical treatment. The indication for intervention is for those patients who have already suffered a cerebrovascular problem and who, with or without sequelae, are prone to repeat it.