Transient ischemic attack

Transient ischemic attack

A transient ischemic attack (TIA) is a brief episode of neurological dysfunction caused by loss of blood flow (ischemia) in the brain, spinal cord, or retina, without tissue death (infarction).[1] TIAs have the same underlying mechanism as ischemic strokes. Both are caused by a disruption in blood flow to the brain, or cerebral blood flow (CBF). The definition of TIA was classically based on duration of neurological symptoms. The current widely-accepted definition is called "tissue-based" because it is based on imaging, not time. The American Heart Association and the American Stroke Association (AHA/ASA) now define TIA as a brief episode of neurological dysfunction with a vascular cause, with clinical symptoms typically lasting less than one hour, and without evidence of infarction on imaging.[1]

TIA causes the same symptoms associated with stroke, such as weakness or numbness on one side of the body. Numbness or weakness generally occur on the opposite side of the body from the affected hemisphere of the brain. A TIA may cause sudden dimming or loss of vision, difficulty speaking or understanding language, slurred speech, and confusion.

TIA and ischemic stroke share a common cause. Both result from a disruption in blood flow to the central nervous system. In ischemic stroke, symptoms generally persist beyond 7 days. In TIA, symptoms typically resolve within 1 hour. The occurrence of a TIA is a risk factor for eventually having a stroke.[1][2] Both are associated with increased risk of death or disability. Recognition that a TIA has occurred is an opportunity to start treatment, including medications and lifestyle changes, to prevent a stroke.

While a TIA must by definition be associated with symptoms, a stroke may be symptomatic or silent. In silent stroke, also known as silent cerebral infarct (SCI), there is permanent infarction present on imaging, but there are no immediately observable symptoms. An SCI often occurs before or after a TIA or major stroke.[3]

Signs and symptoms

Signs and symptoms of TIA are widely variable and can mimic other neurologic conditions, making the clinical context and physical exam crucial in ruling in or out the diagnosis. The most common presenting symptoms of TIA are focal neurologic deficits, which can include, but are not limited to:[4]

A detailed neurologic exam, including a thorough cranial nerve exam, is important to identify these findings and to differentiate them from mimickers of TIA. Symptoms such as unilateral weakness, amaurosis fugax, and double vision have higher odds of representing TIA compared to memory loss, headache, and blurred vision.[5] Below is a table of symptoms at presentation, and what percentage of the time they are seen in TIAs versus conditions that mimic TIA. In general, focal deficits make TIA more likely, but the absence of focal findings do not exclude the diagnosis and further evaluation may be warranted if clinical suspicion for TIA is high (see “Diagnosis” section below).[6]

TIA versus mimics

Symptoms[6] % TIA mimics[6] % TIAs[6]
Unilateral paresis 29.1 58
Memory loss/cognitive impairment 18 to 26 2 to 12
Headache 14.6 to 23 2 to 36
Blurred vision 21.8 5.2
Dysarthria 12.7 20.6
Hemianopia 3.6 3.6
Transient monocular blindness 0 6
Diplopia 0 4.8

Symptoms of TIAs can last on the order of minutes to 1–2 hours, but occasionally may last for a longer period of time.[7][8] TIAs used to be defined as ischemic events in the brain that last less than 24 hours, but given the variation in duration of symptoms, this definition holds less significance.[8] A pooled study of 808 patients with TIAs from 10 hospitals showed that 60% lasted less than 1 hour, 71% lasted less than 2 hours, and 14% lasted greater than 6 hours.[9] Importantly, patients with symptoms that last more than one hour are more likely to have permanent neurologic damage, making prompt diagnosis and treatment important to maximize recovery.[8]

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