The Neuroscience on the Web Series:
CMSD 636 Neuropathologies of Language and Cognition

CSU, Chico, Patrick McCaffrey, Ph.D.


Chapter 1. Medical Aspects: Types of Strokes


Medical Aspects/Prevention of Cerebral Vascular Accidents

A stroke or cerebral vascular accident (CVA) is a temporary or permanent loss of functioning brain tissue caused by an interruption in the cerebral blood supply. This interruption is typically caused by plaque. Recent technology using magnetic resonance imaging (MRA) is being used to evaluate the resulting thrombosis and stenosis in the arteries. The term "brain attack" is now being used by many to refer to stroke.

Approximately 550,000 people have strokes in the U.S. every year. Brain infarctions account for about 75% of strokes, while intracerebral or subarachnoid hemorrhages for about 15%. (Gresham, G., Duncan, P., Stason, W., et al. 1995). According to the National Stroke Association there are approximately 160,000 deaths per year in the United States from stroke. Most strokes correlate with hypercholesterolemia, or excessive levels of cholesterol in the blood. There may be other factors as well because many individuals with high levels of cholesterol do not get strokes. Diabetes and stroke are closely linked, because many of the risk factors for diabetes are also risk factors for stroke. They include high cholesterol levels, obesity, family history, and lack of exercise. Diabetics have other risk factors that make them generally more prone to stroke and heart disease. They include high levels of triglycerides and low levels of high density lipoprotein, the good cholesterol. Diabetics also have a tendency to form clots. Smoking is another serious risk factor for stroke.

A family of drugs called statins include Mevacor, Pravachol, Zocor, Lescol, Lipitor and Baycol. Baycol is a trademark used for the drug cerivastatin. It was pulled off the market in 2001 because of muscle destruction linked to 31 deaths in the United States and at least 9 additional fatalities abroad. Statins are used safely by millions of Americans and others around the world to lower cholesterol levels. While these drugs work well for most, some people have a very rare but dangerous side effect which results in muscle destruction. People suffering muscle pain/tenderness or weakness should notify their physicians immediately. They may have rhabdomyolysis, a life threatening condition in which muscle cells are released into the bloodstream. Niacin is another treatment option to raise good chosterol and lower bad chosterol and triglycerides. It is often used alone or with statins and is much safer. Dr. John Kastelein, 2008, a Dutch scientist led a study comparing the efficacy of Vytorin, a combination of ezetimibe (Zetia) and simvastatin (Zocar), and simvastatin alone. The results indicate that simvastatin alone was much better that Vytorin at reducing plaque. This was true even though Vytorin was very successful at lowering LDL and triglycerides. Vytorin had no added benefit in reducing plaque.

Experimental approaches

There are two principal kinds of strokes, ischemic and hemorrhagic. Both types cause infarction, or death of brain tissue. Ischemic strokes typically result from arterial blockage. The gold standard has been angiography where a catheter is place in the formoral artery in the groin and threaded up through the arteries to the heart or brain. It's invasive especially for arteries that supply blood to the brain. A magnetic resonance imaging technique called MRA is now used to look at artery blockage or stenosis. The image you just saw is that of an arterial venous malformation (AVM). Please look at the video of a woman who had a stroke due to an AVM.

Other recent medical advances may offer hope to many stroke patients. At a meeting in San Francisco of the American Association for the Advancement of Science, Dr. Paul Sanberg of the University of South Florida described his stem cell research. Cells recovered from umbilical cords may be useful for repairing brains damaged by stroke. In experimentation with animals these cells were infused through the blood stream without the need for surgical implantation into the brain. Dr. Sanberg is hopeful that this approach can be used with human stroke victims within the next two years. In experiments with rats, Sanberg's team found that those given the cells had recovered about 80% from the strokes, while the control group (untreated rats), had made only a 20% recovery. Sanberg feels that the treatment works best when give within 24 hours of injury. According to Sandberg, just how the new cells rewire the brain is unclear even though the cells can take on the form of different types of brain tissue. He also said that one or two umbilical cords could very likely be enough to treat one human stroke victim. He cautions that many things such as immune system responses and the numbers of cells to be infused have to be worked out before any treatment can begin with humans.

Another, quite different approach to helping stroke victims recover is the lowering of body temperatures. At a meeting of the American Stroke Association in Fort Lauderdale, Florida, Dr. Derk Krieger from the Cleveland Clinic described how he and his colleagues used hypothermia (alcohol rubs) to quickly reduce body temperature of patients following severe strokes. In order to prevent shivering, the patients had to be temporarily paralyzed, put on breathing machines, and rendered unconscious. It is still an experimental procedure, which may be very uncomfortable, and result in complications. Even so, of the ten patients who underwent the procedure, five had no permanent damage.

The FDA has approved the use of thrombolytic therapy (t-PA) for the treatment of acute stroke within three hours of onset of symptoms (Atkinson, 1997). According to Dr. Atkinson, in a NINDS t-PA for stroke trial, patients treated with t-PA therapy improved regardless of the suspected etiology of the stroke. However, episodes of systemic bleeding in the 10 days after therapy were 6.4% with t-PA and 3.8% with a placebo. The study which treated 624 patients showed that patients treated with t-PA were 30-50% more likely to have minimal or no disability at three months. A surprise finding of the study was that patients treated within 90 minutes after onset of symptoms did not do better than patients treated after three hours. Also, there was no evidence that transient ischemic attacks (TIA's) played a role in the study, because only 2% of placebo treated patients were normal at 24 hours. Remember, a TIA presents with stroke symptoms but they go away within a day, leaving the patient pretty normal. The New England Journal of Medicine on 9/25/'08 reported that the 3 hour window to administer t-PA after symptoms start has been increased to 4.5 hours. Apparently the clot dissolver can be safely given more than an hour longer than the previous recommendation.

Another treatment for ischemic stroke that has been investigated is the use of a direct thrombin inhibitor. According to Marion LaMonte, 2001, the drug Argatroban was examined for safety and efficacy in patients with acute ischemic stroke. With ischemia, blood supply to the brain is interrupted either by a blockage or a narrowing of an artery. Argatroban is an anticoagulant. It may work on dissolving the primary clot as well as affecting the microcirculation around the area of the original blockage. According to Michael Chopp, Ph. D. 2001, Vice Chair of neurology at Henry Ford Hospital, in studies with rats, combining Argatroban with t-PA at four hours post onset has potential to open the window of opportunity for stroke treatment without increasing intracranial bleeding. Another study examined the experimental drug DHA. This antioxidant scavenges oxygen free radicals that can play a major role in tissue damage. During a brain attack there is a reduction in blood flow. This permits free radicals to affect the body's ability to neutralize toxins. DHA is a derivative of ascorbic acid-vitamin C. After DHC is transported across the blood brain barrier it is converted into vitamin C.

Ischemic Strokes

The term "ischemia" refers to a lack of blood-borne oxygen. Ischemic strokes are more common than hemorrhagic strokes and may be caused by stenosis or thrombosis of the arteries, as well as by the presence of thrombo-emboli in the arteries. Check out the Department of Neurology at Debrecen University Medical School, Hungary.

Stenosis is a general term that means narrowing. In this case, it refers to the narrowing of an artery due to the build-up of plaque. As the artery is not completely blocked, some blood passes through it. However, if 50% of normal blood pressure is not maintained, brain damage will occur.

Thrombosis refers to the total blockage of an artery due to plaque build-up or emboli.

There are a number of drugs taken for heart and circulatory disease that have been shown to slow the build up of plaques that block the internal carotid arteries. The internal carotids take blood to the middle cerebral and anterior cerebral arteries. Blockages in the internal carotids can result in stroke that affects language, speech, and cognition. A study by researcher Dr. Goran Berglund (2001) and his team at Malmo University in Sweden that came out on in the American Heart association Journal, Circulation, reported the first evidence that a beta blocker can slow progression of plaque in the internal carotids. The drug used was metoprolol. It slowed the buildup rate by 40% in otherwise healthy people who had plaque buildup with no overt symptoms. The study involved 793 people aged 49 to 70. Another study by researchers in Canada, also reported in Circulation, showed that ramipril, an ACE inhibitor, slowed the formation of plaques in the internal carotids.

Currently only tissue plasminogen activating agents (t-PA) is approved by the FDA for therapy for acute ischemic stroke. This potent medicine carries with it a risk of cerebral hemorrhage. According to Bhatnager, 2008, it must be administered intravenously within three hours of CVA onset or inter-arterially within six. Drugs that inhibit platelets such as aspirin and Plavix are often used after a person has transient ischemic attacks. Many people who are at risk for stroke are advised by their doctors to take an 80mg aspirin every day.

Thrombo-emboli are pieces of plaque which break loose from thrombi and travel through the arterial system until they reach a narrow area and lodge, cutting off the blood supply to brain tissue beyond that point. This can occur when a normally sedentary person engages in strenuous physical activity.

 

TIAs or Transient Ischemic Attacks

Two different types of temporary ischemic events are warning signs that a true stroke is likely to occur in the near future. They are transient ischemic attack (TIA) and reversible ischemic neurological defect (RIND).

These are transient disturbances of the blood supply to a localized part of the brain, which produce a temporary, focal lesion. Unlike strokes they resolve in spontaneous and complete recovery.

Symptoms of TIAs mimic those of stroke. These attacks may cause temporary aphasia, numbness, and impair speaking, reading, and writing abilities. Dizziness and visual problems, such as blindness in part of the visual field, can also occur. Sometimes, TIAs are very mild and involve only numbness in a limb, or loss of sight in one eye. Severe TIAs cannot be differentiated from a stroke until recovery occurs.
A TIA typically last between 2 and 15 minutes, although such an event could conceivably last as long as 24 hrs. It is also possible to have a series of many brief TIAs during one day. For example, a patient might have 10 or more transient ischemic attacks within a 24 hr. period.

As mentioned above, drugs such as aspirin or Plavix are often prescribed after a TIA.

RIND or Reversible Ischemic Neurological Defect

A RIND is a lengthy TIA. The term RIND is usually applied to attacks that continue for more than 12 hours without interruption, although some may last for several days. As with a TIA, a RIND will resolve in complete recovery, however some neurologists do not consider them temporary. (There is some evidence that RINDs do cause some subtle neurological damage, but these minor changes are nothing like the types of disabilities seen after "real" strokes.)

Ischemic strokes, as well as TIAs and RINDs, are more likely to occur early in the morning. During sleep, blood pressure is at its lowest level. When a person gets out of bed, the sudden increase in blood pressure due to this change in activity level can cause an embolism to break free.

Hemorrhagic Strokes

Hemorrhagic stroke occurs when a cerebral artery ruptures, causing bleeding within the cranium. Such ruptures may be caused by aneurysms or weak spots in arterial walls. (Aneurysms can balloon out rather than bursting. The excess pressure resulting from this swelling can also damage brain tissue.) Bleeding due to stroke can cause the formation of hematomas, or pools of congealed blood, in the epidural space, or the subdural space.

Intraparenchymal bleeding refers to the flow of blood into brain tissue rather than into an existing space like the subarachnoid space or a potential space like the subdural space. The term "parenchyma" means "specific cells of a gland or organ" (Stedman's Concise Medical Dictionary. 1997) Parenchymal hemorrhages occur most frequently in the putamen (part of the lenticular nucleus), thalamus, pons, or cerebellum (Coch & Metter, 1994). The striata artery which supplies the internal capsule with blood is quite thin and easily hemorrhages. This is why it is called the artery of stroke.

Before the advent of sophisticated scanning techniques that allow the identification of small as well as large hematomas, it was believed that prognosis after a hemorrhagic stroke was extremely poor. Now it is recognized that patients often make a better recovery after a hemorrhagic stroke than after an ischemic stroke. Slow parenchymal bleeding may irritate brain tissue rather than damaging it. As the brain absorbs some of the blood flow from the hemorrhage, these areas heal and begin to function again. It is possible for a patient to make a complete recovery from a hemorrhagic stroke.

Because it frequently occurs at a very slow rate and over a lengthy period, neurological problems due to parenchymal bleeding may have an extended spontaneous recovery. For this reason, it may justifiable to continue therapy for a longer period of time with patients who have had parenchymal bleeding than with those who have had other types of hemorrhages.

Strokes can also be divided into the categories of completed or progressive.

Completed strokes are the type most commonly seen. In this case, the infarction of brain tissue has ceased to occur.

Progressive strokes are those that are still evolving, meaning that the patient's condition is continuing to deteriorate. Progressive strokes can last for a week or more. This condition is usually the result of a severe hemorrhage.

If called in to evaluate patients with this diagnosis, the SLP should test the patients but explain in the report that major changes could occur shortly. Even if their aphasia is initially mild it could worsen. Particular caution should be used when evaluating the swallowing status of such patients. They may be able to swallow safely initially, but develop dysphagia later as their condition worsens. Also, progressive strokes tend to happen to people who have very poor cerebral vascular health and are therefore at risk for having another stroke very soon. Cerebral vascular accidents are only some of the medical conditions that result in aphasias and right hemisphere syndrome. Also included are tumors and metabolic encephalopathy. In addition patients may have dementia. I just read a study on coffee and prevention of dementia.


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Other courses in the Neuroscience on the Web series:
CMSD 620 Neuroanatomy | CMSD 642 Neuropathologies of Swallowing and Speech

Copyright, 1998-2011. Patrick McCaffrey, Ph. D. This page is freely distributabl.