Updated Definition of Stroke Incorporates Decades of Research

SAN DIEGO—A panel of clinicians and researchers has developed an updated definition of stroke, Scott Kasner, MD, reported at the 2014 International Stroke Conference. The new definition has been drafted as a replacement for a provisional definition that the World Health Organization drafted in 1980 and incorporates scientific and technologic advances that have occurred since that time.

The new definition of CNS infarction is “brain, spinal [cord], or retinal cell death attributable to ischemia, based on either pathologic imaging or other objective evidence of cerebrospinal cord or retinal ischemic injury in a defined vascular distribution, or clinical evidence of ischemic injury, based on symptoms persisting [for] greater than 24 hours,” said Dr. Kasner, Professor of Neurology at the Hospital of the University of Pennsylvania in Philadelphia. “This [version] has preserved some of the old definition, but only as a fail-safe when we don’t have sufficient imaging or other objective evidence,” he added. The new definition is consistent with the current definition of myocardial infarction as the presence of cell death due to prolonged ischemia.

Scott Kasner, MD

The Clinical Spectrum of CNS Infarction
In an article published in the July 2013 issue of Stroke, the panel, which included members of the American Heart Association and the American Stroke Association, defined distinct clinical entities within the broad category of CNS infarction. They defined ischemic stroke as “an episode of neurologic dysfunction caused by focal cerebral, spinal, or retinal infarction,” explained Dr. Kasner. The new formulation redefines classic transient ischemic attacks (TIAs) as cerebral infarctions because patients with TIA have evidence of infarction on a scan. As a result, the new definition includes “probably about a third of TIAs,” said Dr. Kasner.

Defining silent infarction is difficult precisely because it is not accompanied by symptoms. “We can define these somewhat reliably using a definition from the Cardiovascular Health Study: greater than 3-mm lesions in a vascular distribution [with] no mass effect,” said Dr. Kasner. Silent infarctions occur in as much as 30% of apparently healthy individuals and are associated with subtle cognitive and gait deficits. Because patients with silent infarctions are at high risk for subsequent stroke and dementia, the panel decided to include silent infarction under the rubric of stroke. “This [definition] is a big paradigm change for all of us,” noted Dr. Kasner.

Another change is evident in the panel’s treatment of hemorrhagic stroke. Although common, this term “is confusing because it includes intracerebral hemorrhage, subarachnoid hemorrhage, and probably hemorrhagic conversion of an infarction, [which are] three different disorders,” said Dr. Kasner. Consequently, the panel recommends that the term “hemorrhagic stroke” be abandoned.

Intracerebral hemorrhage was defined as a focal collection of blood within the brain, parenchyma, or ventricular system not caused by trauma. Stroke caused by intracerebral hemorrhage was defined as neurologic symptoms associated with this condition. The panel defined subarachnoid hemorrhage as bleeding into the subarachnoid space, and stroke caused by subarachnoid hemorrhage as neurologic symptoms associated with subarachnoid blood.

Data on hemorrhagic conversion of infarction are scarce, and achieving a consensus definition of this entity was difficult, said Dr. Kasner. The panel defined it as a small mass of blood within an obvious infarction but suggested that it instead be considered cerebral infarction or, if symptoms are present, ischemic stroke. Parenchymal hemorrhages that cause mass effect “behave like intracerebral hemorrhages, and we could probably reasonably call them that,” said Dr. Kasner. “But, fundamentally, they’re still hemorrhagic conversion of infarctions, and hemorrhagic stroke is a confusing term.”

Cerebral venous thrombosis can cause infarction, hemorrhage, and edema, but it usually causes headache, intracranial hypertension syndrome, or cranial nerve abnormalities without CNS injury. “To be clear, cerebral venous thrombosis is only a stroke if it causes infarction or hemorrhage in the CNS and does not include reversible edema,” explained Dr. Kasner.

Several Questions Remain Unanswered
The panel noted that several questions about stroke remain unanswered. For example, it is unclear how to diagnose patients during the first 24 hours of an event before imaging has been conducted. “[Do they have] TIA? Are they going to get better or [do they have] stroke? We don’t know,” said Dr. Kasner. “We suggested that we use a term like ‘acute cerebrovascular syndrome,’ similar to acute coronary syndromes, which could include unstable angina or myocardial infarction, while we’re trying to pin down the diagnosis.”

In addition, the proper treatment for patients with silent infarctions is unclear. “It certainly makes sense to treat their risk factors of hypertension [and] hyperlipidemia,” said Dr. Kasner. But no consensus exists about whether to treat such patients with other antiplatelet therapies. Neurologists also disagree about whether to consider a patient with carotid stenosis and silent infarction symptomatic or asymptomatic.