Definition of transient ischemic attack
- Karen L Furie, MD, MPH
Karen L Furie, MD, MPH
- Chair and Professor of Neurology
- Alpert Medical School of Brown University
- Hakan Ay, MD
Hakan Ay, MD
- Associate Professor of Radiology
- Massachusetts General Hospital
- Harvard Medical School
Transient ischemic attack (TIA) is a brief episode of neurologic dysfunction resulting from focal temporary cerebral ischemia not associated with cerebral infarction.
TIA was originally defined clinically by the temporary nature (<24 hours) of the associated neurologic symptoms. However, the arbitrary nature of the 24-hour time limit and lack of specific pathophysiologic meaning hampered the clinical and research utility of the term "TIA." Recognition of these problems led to a change to a tissue-based definition of TIA. The change was driven by advances in neuroimaging that enabled very early identification of ischemic brain injury.
An overview of the classic and modern definitions of TIA is provided here. The etiology, clinical manifestations, diagnosis, treatment, and prevention of TIA are discussed separately. (See "Etiology and clinical manifestations of transient ischemic attack" and "Initial evaluation and management of transient ischemic attack and minor ischemic stroke" and "Secondary prevention for specific causes of ischemic stroke and transient ischemic attack" and "Overview of secondary prevention of ischemic stroke".)
As endorsed by consensus statements from the American Heart Association and American Stroke Association (AHA/ASA), transient ischemic attack (TIA) is defined as a transient episode of neurologic dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction . Central nervous system (CNS) infarction is defined as brain, spinal cord, or retinal cell death attributable to ischemia, based on neuropathologic, neuroimaging, and/or clinical evidence of permanent injury . Ischemic stroke is defined as an episode of neurologic dysfunction caused by focal cerebral, spinal, or retinal infarction. Silent CNS infarction is defined as imaging or neuropathological evidence of CNS infarction without a history of acute neurological dysfunction attributable to the lesion.
TIA was originally defined as a sudden onset of a focal neurologic symptom and/or sign lasting less than 24 hours, presumably brought on by a transient decrease in blood supply, which rendered the brain ischemic in the area producing the symptom. However, this classic definition of TIA was inadequate for several reasons. Most notably, there is risk of permanent tissue injury (ie, infarction) even when focal transient neurologic symptoms last less than one hour. Thus, the benign connotation of "TIA" has been replaced by an understanding that even relatively brief ischemia can cause permanent brain injury. (See 'Relationship of symptom duration and infarction' below.)
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