Stroke Health Article

STROKE

Stroke, or cerebrovascular accident (CVA), is the third leading cause of death (after heart disease and cancer) in the United States and the industrialized countries of the world. The term "stroke," which comes from subjects being suddenly "struck down" with neurological deficits, is commonly used by both professional and lay groups. Efforts are being made to replace the term with "brain attack" to dramatize its analogous effects to a "heart attack," the term used for myocardial infarction. The term "cerebrovascular accident" is used interchangeably with stroke ("accident" indicates the catastrophic nature of strokes, not a traumatic origin as the term implies). More than 600,000 strokes occur annually in the United States, according to the American Heart Association, and stroke prevalence (number of living stroke victims) is approximately 4.5 million with an annual cost in 1997, both direct and indirect, of over $40 billion.

Stroke refers to the usually sudden onset of a neurological deficit, such as hemiparesis (weakness on one side of the body), or aphasia (impairment of language comprehension and production), which can be attributed to either the occlusion or rupture of a cerebral vessel. Resulting specific neurological symptoms and signs are determined by the area of the brain that is affected, and since the complex functions of the brain are either localized in specialized areas or diffusely distributed, stroke symptoms may similarly be localized or generalized in nature. For example, the long pathway of motor fibers can be interrupted, with resulting hemiparesis involving various cerebral arteries or their branches, such as the anterior, middle, or vertebrobasilar arteries. Occlusion of smaller arterioles which feed smaller areas of brain may result in more isolated effects, such as pure sensory or motor hemiparesis. On the other hand, occlusion or rupture of vessels in "silent" areas of the brain, as in the frontal or parietal cortex, can lead to subtle nonfocal symptoms reflected in impaired cognition, executive function, or memory. Other symptoms of impaired specialized brain functions from strokes include apraxia (impairment in the execution of motor actions), and agnosia (loss of ability to recognize familiar objects). Leukoaraiosis, or increased T2-signal intensity, on magnetic resonance imaging (MRI) of brain white matter results predominantly from small-vessel disease, and this syndrome is associated with increased risks for strokes and dementia.

ISCHEMIC STROKES

The causes of arterial occlusion, or ischemic strokes, are multiple. The most frequent is atherosclerotic disease of extracranial and/or intracranial arteries; the former is more common in Caucasians, while the latter is more frequent among African Americans and Asians. A thrombus (stationary blood clot) formed on atherosclerotic plaques in these locations, as well as on the aorta, can dislodge and embolize to occlude a distal artery. Strokes due to atherosclerosis account for approximately two-thirds of all strokes. If seen within three hours of stroke onset, treatment with tissue plasminogen activator (tPA), a thrombolytic agent, may substantially improve a patient's neurological outcome. Otherwise, therapeutic efforts are aimed at optimizing cerebral blood flow to ischemically impaired brain tissue, providing neural protection to avert brain damage, and maximizing neurorehabilitation. Research on stem cell and neural progenitor cell implantation into an ischemically damaged brain to promote recovery is a recently promising area of stroke research.

Transient Ischemic Attacks (TIAs). Strokes may be heralded by transient neurological deficits, called transient ischemic attacks (TIAs), such as temporary blindness of one eye (amaurosis fugax), hemiparesis, or aphasia. Most frequently, TIAs occur with significant atherosclerotic disease of the extracranial carotid arteries. Control of risk factors for atherosclerosis, such as hypertension, smoking, diabetes mellitus, elevated cholesterol, stress, and, perhaps, sedentary lifestyle, will hopefully minimize strokes from this cause to an irreducible minimum. For significant extracranial disease (>70% diameter stenosis [constriction] at the carotid bifurcation), carotid endarterectomy in competent surgical hands has been shown to reduce stroke recurrence significantly. Aspirin and other antiplatelet drugs in nonsurgical candidates can prevent subsequent strokes.

Cardiogenic strokes. Ischemic strokes can be caused by emboli from the heart as a result of more than a dozen cardiac disorders, the most common being arrhythmias, particularly atrial fibrillation (AF). Suspected cardiogenic strokes require workup, including transthoracic and transesophageal echocardiography (TTE and TEE), which can detect valvular pathologies, wall-motion abnormalities, thrombi, and patent foramen ovale (PFO). This group, in aggregate, may account for up to a quarter or more of all ischemic strokes. For AF, the treatment of choice to prevent embolic strokes is long-term anticoagulation. Patients who are not anticoagulation candidates should be treated with antiplatelet drugs. Conditions such as PFO can be treated medically with anticoagulation; surgical and percutaneous options are also available for PFO closure.

Lacunar Strokes. These strokes refer to small branch occlusions (noted previously), and include discrete syndromes such as pure sensory and motor hemiparesis. Lacunar strokes result primarily from chronic sustained hypertension, and the pathological change is "lipohyalinosis" of arterioles. This syndrome may account for 10 to 15 percent of all strokes. Adequate control of hypertension should prevent this condition.

Two final categories of diseases-causing ischemic strokes are more frequently considered in younger persons, especially those under fifty-five years of age, and involve arteries and blood elements. For the former, vessel diseases other than atherosclerosis include inflammatory processes, such as the arteritides; migraine; dissection—either spontaneous or traumatic; moyamoya syndrome; fibromuscular disorders; MELAS syndrome (mitochondrial encephalopathy, lactic acidosis, and stroke-like symptoms) and a few others. For the latter, blood-element disorders include clotting, and platelets and erythrocyte abnormalities. The most common clotting disorders are resistance to protein C activation—most frequently due to Factor V Leiden mutation (506Q); antiphospholipid syndrome, which includes the lupus anticoagulant and anticardiolipin antibodies; reduced antithrombin III; protein C & S deficiencies; plus a few others. Treatment of vascular disorders is tailored to the individual condition; for example, migraine is treated with prophylactic agents, which prevent vasospasm; arteritides with steroids and immunosuppressive agents; and moyamoya syndrome with a variety of bypass surgical procedures. Many of the hypercoagulable or prothrombotic conditions are treated with long-term anticoagulation.