What is Moyamoya Disease?
Moyamoya disease was first mentioned in Japanese medical literature back in 1957, and named “moyamoya disease” in 1969 by Suzuki and Takaku. It’s a condition that generally affects both sides of the brain, where the cause is still unknown. This disease is characterized by a gradual narrowing of the ends of two important blood vessels in the brain – the internal carotid artery and the circle of Willis.
There is also a related condition known as Moyamoya syndrome, which shows the same symptoms but is associated with other neurological or non-neurological disorders, which could be either inherited or developed over time.
One of the ways the body responds to the reduced blood flow caused by this disease is by creating a network of extra blood vessels, mainly at the base of the brain. These new vessels serve to compensate for the diminished blood supply in the brain. They are known as moyamoya vessels – a phrase that means “something hazy like a puff of smoke drifting in the air” in Japanese, which is used to describe their appearance.
What Causes Moyamoya Disease?
Some people can inherit conditions from their parents that make them more likely to have certain health issues. For example, those with Sickle Cell Disease or trait, or Down Syndrome, might have a higher risk of developing certain conditions. Another example is Neurofibromatosis type 1, which is often linked to other health issues.
There are also conditions that you can develop over time – that’s what we call acquired conditions. Some of these include exposure to radiation in the head or neck, chronic meningitis (a long-term inflammation of the protective membranes covering the brain and spinal cord), or having a tumor at the base of the skull.
Other acquired conditions could be atherosclerosis of skull base arteries, which means the hardening and narrowing of the arteries at the base of your skull. Arteriosclerosis, in general, refers to the hardening and thickening of the arteries throughout the body. Cerebral vasculitis, which is an inflammation of the blood vessel wall involving brain, is another condition that can be acquired.
Risk Factors and Frequency for Moyamoya Disease
Moyamoya disease (MMD) typically starts showing symptoms at two specific age ranges: 5 to 9 years and 45 to 49 years. This illness is most prevalent in East Asian countries, particularly Japan and Korea. However, an increase has been noted in Western countries as well. A study conducted in California and Washington involving 298 patients reported that the occurrence of MMD was 0.086 per 100,000 people.
Recent research conducted in East Asian countries discovered a family history of MMD in 10% to 15% of patients, according to data from 2000 to 2011. The same study also identified a higher occurrence of MMD in women, with a ratio of 2.2 women for every man. In a more updated study utilizing the Nationwide Inpatient Sample database, it was observed that MMD is spread among races in a way that mirrors their relative proportions in the US population. The most common reason for hospital admission due to MMD was ischemic stroke, a condition caused by an obstruction in the blood supply to the brain.
- MMD tends to begin showing symptoms in people aged 5 to 9, and 45 to 49.
- This disease is most common in East Asian countries, but it’s becoming more common in the West.
- About 10% to 15% of MMD patients have a family history of the disease.
- Women are more likely to be affected, with 2.2 women for every man diagnosed.
- In the US, the incidence of MMD is distributed among races according to their relative proportions in the population.
- The most common reason for hospital admission due to MMD is an ischemic stroke.
Signs and Symptoms of Moyamoya Disease
Moyamoya disease often shows up as episodes of reduced blood flow to the brain and can lead to minor or significant strokes. Other signs may be bleeding in the brain primarily in adults, and seizures in both adults and kids. Symptoms can be split into two primary groups:
- Symptoms caused by reduced blood flow to the brain, including stroke, transient ischemic attack (brief stroke-like attacks), and seizure.
- Symptoms due to the growth of extra blood vessels to make up for the restricted blood flow, like bleeding in the brain and headaches.
In kids, Moyamoya most commonly starts with brief stroke-like attacks or actual strokes. These bouts are often triggered by hyperventilation when crying, playing a wind instrument, or eating hot noodles. Over-breathing lowers carbon dioxide levels, which causes the brain’s blood vessels to constrict, worsening the already deficient blood flow to the brain. Kids might also show cognitive decline or learning disabilities, which are linked to the number of strokes and chronic low oxygen levels due to narrowing of the brain’s blood vessels.
Adults with Moyamoya, besides experiencing brief stroke-like attacks or strokes, can often have hemorrhagic strokes caused by a rupture of fragile moyamoya collateral blood vessels. These occur mainly in deep parts of the brain, such as the basal ganglia or periventricular deep white matter. Bleeding within the ventricles of the brain is common due to the closeness to the main site of brain bleeding. Seizures are common complications of either type of stroke. Migraine-type headaches are common in both kids and adults and probably occur due to stimulation of pain receptors in the outer coverings of the brain by dilated trans-dural collaterals.
Testing for Moyamoya Disease
MRI, or Magnetic Resonance Imaging, is often one of the initial tests done when there’s a suspicion of brain-related issues due to its sensitivity and non-invasiveness. It can help identify issues like bleeding or strokes in the brain tissue, and can even display changes in the flow of fluid within the brain.
Magnetic Resonance Angiography (MRA) is another test often used, and it’s considered the gold standard when looking at the blood vessels within the brain. It can give doctors an idea of how the arteries are functioning and if there’s any narrowing or blockages. Depending on what is seen in the MRA, it can help doctors diagnose conditions such as Moyamoya disease or Moyamoya syndrome, conditions that are characterized by blockages or narrowing of the arteries in the brain.
Conventional cerebral angiography is another test used, and it’s the most precise way to see areas and degree of narrowing inside the brain’s arteries. However, its use is minimal due to its invasive nature and other potential risks, and is usually used when the diagnosis is unclear from MRI/MRA results, or before surgery.
Two kinds of extra blood vessel pathways, or collaterals, can be seen in angiography. These pathways develop when the normal routes are blocked. The types of collaterals seen can also help doctors place the progress of the disease into different ‘stages’.
Another tool is Transcranial Doppler (TCD), which helps in monitoring the blood flow in the brain, and Electroencephalography (EEG) that is useful in patients who have had seizures. Suzuki and Kodama found a unique EEG feature in some Moyamoya patients called the ‘Rebuild-up’ phenomenon. It’s a pattern of slow waves that can suggest diminished blood flow.
Several tools exist for measuring blood flow in the brain, like SPECT, or Single-Photon Emission Computed Tomography, and certain types of CT and MRI scans. Such scans can offer information on blood flow distribution and the brain’s response to certain substances, providing insights into its reserve capabilities.
When doctors suspect a condition called Moyamoya syndrome, they might require other tests specific to the conditions associated with it.
Treatment Options for Moyamoya Disease
Moyamoya disease is a condition that affects the brain’s blood vessels, limiting the blood flow to certain areas of the brain. Currently, there is no cure for this disorder. But early diagnosis and appropriate surgical intervention can help manage the disease effectively. Although there are some medications that can help prevent complications associated with the disease, they aren’t capable of stopping the disease from progressing.
For patients with moyamoya disease, the primary focus is to maintain the brain’s blood flow and prevent strokes. Aspirin, a common medication, is often used in treatment plans in order to reduce the chances of further strokes. Even though there’s no solid evidence showing aspirin is directly effective in stroke prevention for moyamoya patients, its use is justified considering it can prevent blood clot formation, especially after surgical treatment that increases blood flow.
Besides controlling strokes, managing seizures and headaches are other symptoms addressed in treatment. Pain relievers and anti-seizure medications can help manage these symptoms.
Surgery is another major treatment for this disease, especially consequential when brain scans show reduced blood flow or signs of potential stroke. Every patient’s case is unique, so surgical decisions are made on an individual basis. For children, surgery tends to be more beneficial as the disease often progresses faster in younger patients.
There are two main types of surgery: indirect and direct revascularization. Indirect revascularization, although simpler to perform, takes a longer timeline to improve brain blood flow compared to direct revascularization. This approach involves borrowing vessels from other parts of the body to help improve blood supply to the brain.
On the other hand, direct revascularization involves creating a new pathway for blood to reach the brain using the patient’s own blood vessels. While this type of surgery produces more immediate results, it is technically more challenging and needs a skilled surgeon to perform it.
What else can Moyamoya Disease be?
When symptoms of particular brain afflictions come up, doctors often have to consider a range of possibilities. These could include:
- Stroke affecting the front of the brain
- Clot in the basilar artery at the back of the brain
- Disorders affecting the blood
- Problems relating to the cavity behind the eyes (Cavernous sinus syndromes)
- Bubble in a brain blood vessel that might burst (cerebral aneurysms)
- Damage to brain’s blood vessels (dissection syndromes)
- Fabry disease, which affects the body’s ability to break down fats
- Muscle and tissue disorders (fibromuscular dystrophies)
- Bleeding inside the skull (intracranial haemorrhage)
- A type of brain tumor in children (Pediatric craniopharyngioma)
What to expect with Moyamoya Disease
The future health outlook for patients with Moyamoya disease can differ greatly from person to person. Unfortunately, for two out of every three patients, the condition tends to worsen over five years, leading to poor outcomes. This worsening occurs regardless of how severe the symptoms are, the type of treatment used, or factors like age, gender, and where the disease is located in the body.
However, according to data from North American studies, 13.3% and 1.7% of patients experience strokes caused by a blood clot (ischemic) or bursting of blood vessels (hemorrhagic), respectively. Certain factors may contribute to a poorer health outlook, including experiencing a hemorrhagic stroke at the start of the disease, being female, having a family history of the disease, and developing the disease at a young age.
In addition to these factors, having a thyroid disorder or being a smoker can negatively impact the overall health outlook in people with Moyamoya disease. But on a brighter note, an early surgical procedure to improve blood flow (revascularization) could lead to a better overall health outlook.
Possible Complications When Diagnosed with Moyamoya Disease
The major complications mostly occur during or after the operation. These include:
- Ischemic stroke during operation (in advanced Suzuki stage of Moyamoya disease)
- Postoperative ischemic stroke that results in a permanent neurological deficit (occurs in 0.9% -8% of patients, and more frequently in adults)
- Hemorrhagic stroke (occurring in 0.7%-8% of patients)
- Postoperative epidural hematoma (Occurs in 4.8% of the pediatric population)
- Hyper-perfusion syndrome after direct vascularization (occurring in 21.5% -50% of patients)
- Scalp problems, especially scalp ischemia (occurs in 17.6%- 21.4% of patients)
