Characteristics of Stroke

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According to the World Health Organization, a stroke consists of "rapidly developing clinical signs of focal (at times global) disturbance of cerebral function, lasting more than 24 hours or leading to death with no apparent causes other than that of vascular origin." "Global" refers to patients in deep coma and those with subarach-noid hemorrhage. This definition excludes transient ischemic attacks (TIAs), a condition in which signs last less than 24 hours.

Strokes are the most common life-threatening neurological disease and the third leading cause of death, after heart disease and cancer, in Europe and the United States. Death rates from strokes vary with age and sex; for example, in the United States, the rates for males are 11.9 per 100,000 for those aged 40-44 and 1,217 per 100,000 for those aged 80-84. For females, the respective rates are 10.9 and 1,067. Large differences in cerebrovascular disease (CVD) mortality have been noted among races. For example, in the United States, mortality is 344 per 100,000 for nonwhites but 124 per 100,000 for whites. Among countries, differences in mortality from stroke ranged from 70 per 100,000 in Switzerland to 519 per 100,000 in Japan.

Decline in CVD deaths has occurred in all developed countries since 1915, and the decline accelerated in recent decades. The acceleration seems related to a decline in incidence. Strokes, however, are more disabling than lethal: 2030 percent of survivors become permanently and severely handicapped. Moreover, recurrent strokes are observed in 15-40 percent of stroke survivors.

Apart from age, the most important risk factor for CVD is arterial hypertension. Control of severe and moderate, and even mild, hypertension has been shown to reduce stroke occurrence and stroke fatality. Cardiac impairment ranks third, following age and hypertensive disease. At any level of blood pressure, people with cardiac disease, occult or overt, have more than twice the risk of stroke. Other risk factors are cigarette smoking, increased total serum cholesterol, blood hemoglobin concentration, obesity, and use of oral contraceptives.

Strokes are a heterogeneous entity caused by cerebral infarction or, less commonly, cerebral hemorrhage. Cerebral infarction accounts for the majority of strokes. When perfusion pressure falls in a cerebral artery below critical levels, brain ischemia (deficiency of blood) develops, progressing to infarction if the effect persists long enough. In most cases, ischemia is caused by occlusion of an intracerebral artery by a thrombus or an embolus arising from ex-tracranial artery disease or a cardiac source. The main cause of ischemic strokes is atherosclerotic brain infarction, the result of either intra-cerebral artery thrombosis or embolism arising from stenosed (narrowed or restricted) or occluded extracranial arteries.

Lacunar infarction (14 percent of ischemic strokes) is a small, deep infarct in the territory of a single penetrating artery, occluded by the parietal changes caused by hypertensive disease. Cerebral embolism from a cardiac source

(15-30 percent of ischemic strokes) is mainly caused by atrial fibrillation related to valvular disease or ischemic heart disease. Other causes of cerebral infarction are multiple, resulting from various diseases, hemopathies, or coagulation abnormalities. However, in 20 percent of cases, the cause of cerebral infarction remains undetermined.

Intracranial hemorrhage (ICH) accounts for 37 percent of strokes. The main cause of ICH is the rupture of miliary aneurysms that have developed in the walls of interior arteries because of hypertensive disease. Nonhypertensive causes of ICH are numerous.

Clinical manifestations of strokes depend on both the nature of the lesion (ischemic or hem-orrhagic) and the part of the brain involved. In the 1960s, a classification of strokes according to temporal profile was proposed to promote common terminology in discussion of history and treatment.

The term "incipient stroke" (also TIA) was defined as brief (less than 24 hours), intermittent, and focal neurological deficits from cerebral ischemia, with the patient normal between attacks. The term "reversible ischemic neurological deficit" was coined for entirely reversible deficits occurring over more than 24 hours. The term "progressing stroke" (stroke-in-evolution) is applied to focal cerebral deficits observed by the physician to progress in severity of neurological deficit over a period of hours or, occasionally, a few days.

The term "completed stroke" is used when neurological signs are stable and no progression has been noted over 18-72 hours. "Major stroke" is applied when immediate coma or massive neurological deficit occurs. In these cases, chances of recovery and effective treatment are minimal. "Minor stroke," by contrast, is applied to cases where deficits relate to only a restricted area of a cerebral hemisphere, or where the symptoms experienced are of only moderate intensity. With minor strokes, diagnosis and institution of treatment should be rapidly combined to avoid further deterioration and, if possible, facilitate the regression of deficit.

These definitions contain some obvious uncertainties, particularly in categorizing a stroke during the early hours. However, they underscore the fact that the management of a stroke often depends more on its temporal profile and on the severity of neurological deficit than on the nature of the lesion.

Jacques Poirier and Christian Derouesne

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