ARTICLE IN BRIEF
A new consensus document updates definitions of stroke and its subtypes based on an increased understanding of the pathophysiology of cerebrovascular diseases, thanks in large part to MRI scans.
Traditional definitions of stroke generally focused on the duration of signs and symptoms, a rather arbitrary approach that sometimes led to inconsistent and even incorrect diagnoses. Citing a need for “an updated definition of stroke for the 21st century,” the American Heart Association and American Stroke Association have published a new consensus document that likely will promote a more uniform and precise diagnosis of stroke while also expanding the number of patients who fall under the definition.
The new definition of stroke is based on an increased understanding of the pathophysiology of cerebrovascular diseases, thanks in large part to MRI scans. If neuroimaging shows evidence of brain tissue injury, it should be classified as a stroke whether or not there are clinical symptoms, according to the update.
“The existing broad definition of stroke was established more than three decades ago, at time before CT scans and certainly MRI scans were widely available and used,” said Scott E. Kasner, MD, professor of neurology at the University of Pennsylvania who was a lead author of the consensus document, published in the May 7 online edition of the journal Stroke.
“We've added some precision to the definition, but we also opened a can of worms in a way,” Dr. Kasner told Neurology Today. “From a public health perspective, suddenly stroke becomes more prevalent by changing the definition.”
‘SILENT’ EVENTS ARE STROKES
The updated definition of stroke includes what was previously referred to as a “silent infarction” or “silent stroke.” Strokes without any overt clinical symptoms are five times more common than symptomatic strokes, Dr. Kasner said.
“The classic definition is mainly clinical and does not account for advances in science and technology,” according to the consensus document. It noted that the World Health Organization's definition of stroke, which dates back to 1970, describes it as “rapidly developing clinical signs of focal (or global) disturbance of cerebral function, lasting more than 24 hours or leading to death, with no apparent cause other than vascular origin.”
“During the 40 years since this definition was formulated, advances have been made in knowledge about the nature, timing, clinical recognition of stroke and its mimics, and imaging findings that require an updated definition,” the statement said.
It noted that an updated definition for transient ischemic attack (TIA) defines it as transient ischemia specifically without evidence of persistent brain injury.
“If the ischemia caused death of the tissue, it is misleading to designate the ischemia as transient,” according to the new document. “Similarly, ischemia may produce symptoms and signs that are prolonged (and so qualify in older definitions as strokes) and yet no permanent brain infarction has occurred.”
Dr. Kasner said, “The old definition using a simple 24-hour duration is no longer reliable. The definition of stroke must therefore be expanded to include any objective evidence of brain injury regardless of duration.”
Under the new stroke definition, central nervous system (CNS) infarction is defined as “brain, spinal cord, or retinal cell death attributable to ischemia, based on neuropathological, neuroimaging, and/or clinical evidence of permanent injury.”
“Central nervous system infarction occurs over a clinical spectrum: Ischemic stroke specifically refers to central nervous system infarction accompanied by overt symptoms, while silent infarction by definition causes no known symptoms,” according to the new definition. “Stroke also broadly includes intracerebral hemorrhage and subarachnoid hemorrhage.”
PRECISE WORDING IS KEY
Several experts in stroke, who were not involved with the paper, described the consensus document as an important publication. “It's very important to have clear, practical, useable and precise ways to define stroke versus TIA versus some other disease process,” said Mark J. Alberts, MD, clinical vice chair for the department of neurology and neurotherapeutics at University of Texas Southwestern Medical Center in Dallas. When patients are imprecisely labeled, it can set in motion an inappropriate treatment plan or, on the other hand, a lack of follow-up evaluation and preventive treatment, such as antithrombotic medications, that could leave the patient vulnerable to future strokes, he said.
Dr. Alberts said that while some clinicians might initially take issue with certain particulars of the new definition, “it speaks to the fact that our understanding of stroke is evolving.” He said it also serves to underscore that “stroke is a heterogeneous disease.”
Patients sometimes are given vague explanations of their stroke symptoms, being reassured that they only had a “mini stroke” or a “little stroke,” said James C. Grotta, MD, chairman and professor of neurology at University of Texas Medical School at Houston and a member of the Neurology Today editorial advisory board. Dr. Grotta said that when he is on hospital rounds he sometimes hears even neurologists characterize stroke in an imprecise way — for instance, a doctor will say the patient has a “hemorrhagic stroke.”
“You have to think in terms of the pathophysiology,” Dr. Grotta said. A hemorrhage, for instance, could occur as a result of an ischemic event (hemorrhagic infarct), or the hemorrhage could be the primary event (intracerebral hemorrhage). The treatments of the two would be completely different, he said.
Dr. Grotta said that while the new definition of stroke is based in large part on imaging results, it does not diminish the important role of clinical evaluation in making a stroke diagnosis.
“There is still plenty of room for clinical acumen and judgment,” he said, and more precise diagnosing should lead to more optimal treatment. “If you say, ‘Oh, it's just a TIA,’ then you may miss the opportunity to prevent the big one.”
NOT EVERYONE AGREES
Dr. Kasner said the decision to expand the definition of stroke was not without controversy. The final definition was not accepted by the leadership of the European Stroke Organization and the World Stroke Organization, primarily due to the inclusion of silent cerebral infarction within the universal definition of stroke, according to a footnote to the document.
The consensus document also noted the potential for confusion in the collecting and analysis of epidemiologic data. “One of the overarching concerns regarding a shift to an imaging-based definition for stroke is the potential to bias stroke surveillance reporting on the availability of technology to contribute to image-based case ascertainment,” the authors of the document noted. In developing countries where MRI is not common, the diagnosis of stroke may lag compared with places where clinicians can easily order imaging studies.
It may also be more challenging for epidemiologists to study stroke trends over time, since the definition of stroke is expanding.
But there could also be some benefits for researchers. Dr. Alberts said the updated definition of stroke could help with stroke research because “it could broaden the ability to enroll patients in some clinical trials.” He added: “Even if someone didn't have clinical evidence of a stroke, the presence of infarcts on brain imaging studies might make them eligible” for a stroke prevention trial, he said.
DEFINING STROKE AND SUBTYPES
According to the new consensus document, the term “stroke” should be broadly used to include the following:
- CNS infarction: Brain, spinal cord, or retinal cell death attributable to ischemia, based on 1) pathological, imaging, or other objective evidence of cerebral, spinal cord, or retinal focal ischemic injury in a defined vascular distribution; or 2) clinical evidence of cerebral, spinal cord, or retinal focal ischemic injury based on symptoms persisting ≥ 24 hours or until death, and other etiologies excluded. (Note: CNS infarction includes hemorrhagic infarctions, types I and II.)
- Ischemic stroke: An episode of neurological dysfunction caused by focal cerebral, spinal, or retinal infarction.
- Silent CNS infarction: Imaging or neuropathological evidence of CNS infarction, without a history of acute neurological dysfunction attributable to the lesion.
- Intracerebral hemorrhage: A focal collection of blood within the brain parenchyma or ventricular system that is not caused by trauma. (Note: Intracerebral hemorrhage includes parenchymal hemorrhages after CNS infarction, types I and II.)
- Stroke caused by intracerebral hemorrhage: Rapidly developing clinical signs of neurological dysfunction attributable to a focal collection of blood within the brain parenchyma or ventricular system that is not caused by trauma.
- Silent cerebral hemorrhage: A focal collection of chronic blood products within the brain parenchyma, subarachnoid space, or ventricular system on neuroimaging or neuropathological examination that is not caused by trauma and without a history of acute neurological dysfunction attributable to the lesion.
- Subarachnoid hemorrhage: Bleeding into the subarachnoid space between the arachnoid membrane and the pia mater of the brain or spinal cord.
- Stroke caused by subarachnoid hemorrhage: Rapidly developing signs of neurological dysfunction and/or headache because of bleeding into the subarachnoid space, which is not caused by trauma.
- Stroke caused by cerebral venous thrombosis: Infarction or hemorrhage in the brain, spinal cord, or retina because of thrombosis of a cerebral venous structure. Symptoms or signs caused by reversible edema without infarction or hemorrhage do not qualify as stroke.
- Stroke, not otherwise specified: An episode of acute neurological dysfunction presumed to be caused by ischemia or hemorrhage, persisting ≥ 24 hours or until death, but without sufficient evidence to be classified as one of the above.
—Source: AHA/ASA Expert Consensus Document