Transient ischemic attack (TIA) has been a useful clinical term, although agreement on the diagnosis for individual cases has been far from perfect, even among experts. The usefulness of the diagnosis has decreased with improvements in brain imaging and a deeper understanding of the natural history of acute cerebral ischemia.
The current concept of TIA characterizes an ischemic episode in which symptoms are transient and not associated with brain injury. But recent evidence suggests that such episodes do not occur or are extremely rare and that brain injury almost always occurs during these events . Consequently, it is time to reevaluate the conceptual soundness and usefulness of the term AIT.
In 1975, a committee of the US National Institutes of Health considered issues related to the classification and diagnosis of cerebrovascular diseases. Their considerations included transient focal cerebral ischemic attacks about which the committee stated: “These are episodes of temporary and focal cerebral dysfunction of vascular origin, of rapid onset (no symptoms to maximum symptoms in less than 5 minutes and usually less than a minute). , commonly lasts 2 to 15 minutes, but occasionally lasts up to a day (24 hours) . ” These episodes were called TIA or TIA and the maximum duration was arbitrarily set at 24 hours .
This definition was constructed to provide a common basis for distinguishing patients who likely had an underlying cerebral infarction (ischemic stroke) and patients who likely did not have an underlying cerebral infarction (TIA).
As magnetic resonance imaging (MRI) became more commonly used in the 1990s, it became clear that many patients who experienced a TIA had evidence of cerebral infarction on brain imaging. Consequently, a TIA working group of stroke neurologists met to consider and then proposed a new definition of TIA which was published in 2002.
Additionally, many health professionals and the public tend to consider TIAs to be benign , while strokes are considered serious. The task force considered this perception regarding TIAs to be incorrect and considered both TIA and stroke to be on a continuum of serious conditions involving cerebral ischemia .
Both are markers of current or imminent disability and risk of death.
The new imaging studies made clear that the traditional time-based definition of TIA did not differentiate a group of people without permanent brain injury, as originally intended. Additionally, there is nothing specific about a symptom duration of 24 hours, 6 hours, 1 hour, or 5 minutes regarding prognosis.
The group proposed a new definition based on tissue , rather than time. Unfortunately, the inclusion of the 1-hour duration persisted as a remnant of the traditional time-based definition.
In 2009, the American Heart Association/American Stroke Association’s Stroke Council issued a scientific statement for health care professionals titled "Definition and Evaluation of Transient Ischemic Attack . " The statement was based on the final tissue-based definition of TIA: “a transient episode of neurological dysfunction caused by focal ischemia in the brain, spinal cord, or retina, without acute infarction .”
Because ischemic events involving the spinal cord are rare and are not generally considered strokes, these episodes could have easily been omitted from the definition.
However, in this statement, time is no longer mentioned . In 2013, Sacco et al addressed the issue of continuing to consider the definition of TIA as both tissue-based and time-based given the varied use worldwide of different imaging modalities and techniques, especially when evaluating temporal trends in incidence of stroke over a long period.
Advances in imaging have made untenable the view that cerebral ischemia sufficient to cause transient symptoms often does not result in brain injury.
If CT images of the brain are taken after an ischemic event, some infarcts may be visible. If the same brain is imaged with MRI at 0.15-Tesla (T), more infarcts may be evident. At 1.5 T, and then at 3 T, even more infarcts are likely to be visualized, even among patients with transient clinical signs and symptoms. Currently, 7 T and even 11 T superconducting magnets are available, and new highly sensitive methods are being developed to identify cerebral infarction from blood.
Furthermore, histopathological studies have shown that even when frank tissue infarction does not occur, neuronal attrition does. Given the extreme rate of loss of neurons, synapses, and myelinated fibers during each minute of ischemia, it is likely that the preponderance of events defined as TIA, even under the modern definition, are associated with long-lasting brain tissue injury , provided the The physician can be confident that the clinical event was due to transient ischemia or infarction rather than a mimicry of a TIA (eg, focal seizure, migraine aura, metabolic disturbance, or syncope).
According to the 2009 TIA definition, this would mean that TIAs (brief episodes of cerebral ischemia that occur quickly enough to cause only transient symptoms and no permanent brain injury) do not exist .
Rather, all symptomatic focal cerebral ischemic events should be considered cerebral infarcts , which may be minor, moderate, severe, or fatal and may or may not be detected by modern imaging techniques. After all, previous descriptions that "TIAs are mini strokes" were correct.
Symptomatic cerebral infarctions vary, according to the scores of the Stroke Scale of the National Institutes of Health, in presentation of minor (0), mild (1-5), moderate (6-14), severe (≥15) or fatal. In summary, they are all ischemic strokes on a continuum from minimum to maximum. TIAs are minor ischemic strokes.
These events should be called ischemic strokes and the term TIA should be retired.
Cardiologists have faced a similar conundrum of definitions and criteria for acute coronary syndrome (ACS). In ACS, with the progression of measurement of serum aspartate aminotransferase (AST) to lactic dehydrogenase (LDH), to creatine kinase (CK), to CK-MB, to troponins, the prevalence of infarction appears to increase. and true angina without infarction decreases . The term unstable angina has been subsumed under ACS and is less commonly used on its own. The similarity between unstable angina and myocardial infarction is much more important than any difference.
Cerebral and coronary arteries and their ischemic events are not substantially different.
Even if true tissue-negative transient ischemic attacks exist as a rare entity when ideally evaluating for cerebral infarction, the utility of distinguishing TIA from minor stroke remains unclear.
Both have a high risk of future cerebral ischemia , both respond to similar treatments, and both may have similar effects on the patient. Again, this assumes that the doctor can be sure that the episode was not an ischemic imitation. The ABCD 2 score (age, blood pressure, clinical characteristics, duration of TIA, and presence of diabetes) can provide a substantial measure of confidence.
Given this, the time and effort spent defining AIT seems misplaced. Rather, it is time to adopt the term acute ischemic cerebrovascular syndrome suggested above and retire the term TIA. Just as cardiologists have addressed the evolution of their redefinition of ACS, neurologists should address the evolution of their redefinition of acute ischemic cerebrovascular syndrome.
