Many of us are unaware of a relatively common age-related health issue—cerebral microbleeds (CMB, largely symptomless leakage from miniscule blood vessels into surrounding brain tissue). Cerebral microbleeds have been linked to a decline in cognitive functions such as memory, thinking and information processing. The good news is that the condition may be prevented or slowed with changes in lifestyle and proper management of high blood pressure, diabetes, and other medical conditions, a Massachusetts General Hospital (MGH) expert says.
Among the increasing number of studies linking CMB with cognitive decline was a paper published in the February 2014 issue of the Journal of Neurology. In that study, researchers used magnetic resonance imaging (MRI) to scan the brains of patients with documented cognitive impairment who had participated in neuropsychological testing at a memory clinic. They found evidence of a significantly higher prevalence of CMB in those participants who scored worse on cognitive testing compared to those who achieved higher scores.
“CMB affects small areas of the brain,” explains neurologist Anand Viswanathan, MD, PhD, Associate Director of MGH’s Telestroke Services. “The vessels often don’t rupture; they ooze. The disorder is common in the elderly and can occur without symptoms in up to 30 percent of older people.
“Microbleeds are a sign of aging blood vessels. They are often associated with cerebral amyloid angiopathy, or CAA, a condition involving the abnormal accumulation of amyloid proteins within cerebral blood vessels. CAA is present in the brains of an estimated 83 percent of individuals with Alzheimer’s disease (AD), who have accumulations of beta-amyloid plaque between nerve cells. However, although there is a significant overlap between the two diseases, a direct causal link between AD and CAA has not been established. Microbleeds are also associated with stroke pathology: Cerebral hemorrhages are more likely to occur in areas of the brain that have been affected by microbleeds.”
WHAT YOU CAN DO
Although CMB is generally asymptomatic, it may be indicated by a transient ischemic attack (TIA, or mini-stroke), which is characterized by symptoms that last less than 24 hours before disappearing, and cause no permanent brain damage. The National Stroke Association advises calling 911 if you have any of these symptoms of a TIA:
- Sudden numbness or weakness of the face, arm or leg, especially on one side of the body
- Sudden confusion, trouble speaking or understanding
- Sudden trouble seeing in one or both eyes
- Sudden trouble walking, dizziness, loss of balance or coordination
Two possible routes
Small areas of brain damage associated with CMB are thought to trigger cognitive problems when they lead to disruption of communication between brain cells or brain regions. Loss of brain cells associated with CMB has been linked with gradual cerebral atrophy. The microbleeds may also be a marker of other conditions that impair brain functioning over time.
CMB is diagnosed using MRI scans to detect deposits of the iron-storing blood protein hemosiderin in brain tissue near cerebral blood vessels. The microbleeds are the end product of one of two basic processes. One process involves the restriction of the oxygen supply to blood vessels that nourish brain tissue, usually in association with vascular risk factors such as older age, pulmonary disease, high blood pressure, diabetes, or smoking. The lack of oxygen is thought to contribute to a loss of blood vessel flexibility, increasing the likelihood of microscopic tears.
A study presented at the latest annual meeting of the Association for Psychological Science suggests that a stiffening of the aorta, an artery that is a major supplier of blood to the brain, may play a role in the development of CMB. The researchers theorized that rather than absorbing and smoothing out blood pressure increases within its normally flexible walls, a stiffer aorta relays surges in blood pressure directly to the brain’s delicate blood vessels, where the higher pressure raises the risk of microbleeds. The researchers gave cognitive tests to about 500 individuals and measured the stiffness of the participant’s aortas. They found that study participants who showed evidence of the greatest aortal stiffening performed worse on cognitive tests than those with less stiffening.
The second major process that leads to brain microbleeds is the buildup within cerebral blood vessels of beta-amyloid proteins similar to those seen in AD. These deposits usually first become apparent in middle age and then increase over time. The abnormal proteins make the vessels heavier, more brittle, and more likely to leak or rupture as a result of a minor injury or a surge in blood pressure. The protein deposits can also cause an ischemic stroke by blocking blood flow to brain tissue.
CAA usually occurs in the outer portion of the brain, in an area of the cortex called the lobar region. Since hemorrhagic and ischemic strokes more commonly affect areas deep within the brain, CAA is suspected when a brain scan reveals that the outer part of the brain is involved. It’s important that strokes caused by CAA be distinguished from other types of brain hemorrhage, since blood thinners used to reduce the blood clots often involved in ischemic strokes can cause bleeding in CAA patients.
Lowering your risk
Risk factors for CMB involve issues that negatively affect blood vessel health, including:
- Older age
- Hypertension, or high blood pressure
- Use of aspirin or other blood thinners in individuals with CAA
- History of stroke
- Chronic obstructive pulmonary disease (COPD)
“Essentially, CMB may be seen as another marker for blood vessel-related disease,” says Dr. Viswanathan. “Taking steps to preserve the health of your cardiovascular system can help you avoid microbleeds. Good strategies include controlling your weight and blood pressure; managing medical conditions such as high cholesterol, diabetes and COPD; reducing stress; quitting smoking; drinking alcohol in moderation; exercising regularly; and eating a nutritious low-calorie diet with minimal sweets, saturated fats, and unhealthy trans fats, and plenty of antioxidant-rich fruits, vegetables, whole grains, nuts, fish with abundant omega-3 fatty acids, lean meats, legumes, and healthy fats, such as olive and canola oils.
“Since CMB is usually asymptomatic, it’s important to seek professional help if you notice a difference in your memory or have problems carrying out daily activities. Your medical care provider can provide a thorough medical assessment and help you manage any medical condition, such as COPD, high blood pressure, or diabetes, that increases your risk for CMB. Your doctor can also determine whether any blood-thinning medications you are taking might be safely replaced by another medication that would be less likely to cause microbleeds. Be sure to discuss your cognitive symptoms and ask your doctor whether you need a referral to a neurologist for screening for CAA or AD. Tell your doctor about any symptoms of a mild stroke or transient ischemic attack (see What You Can Do), as these may sometimes help indicate the presence of CMB.
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