Case
Mr. G is an 80-year-old man with a pacemaker, peripheral artery disease, atrial fibrillation (AF) on warfarin, and tachy-brady syndrome. He presented after experiencing episodes in which he was unable to speak and had weakness on his right side. He had a normal neurological exam upon arrival to the ED, and his blood pressure was 160/80 mm Hg.
Overview
Transient ischemic attacks (TIAs) are brief interruptions in brain perfusion that do not result in permanent neurologic damage. Up to half a million TIAs occur each year in the U.S., and they account for one third of acute cerebrovascular disease.1 While the term suggests that TIAs are benign, they are in fact an important warning sign of impending stroke and are essentially analogous to unstable angina. Some 10% of TIAs convert to full strokes within 90 days, but growing evidence suggests appropriate interventions can decrease this risk to 3%.2
Unfortunately, the symptoms of TIA have usually resolved by the time patients arrive at the hospital, which makes them challenging to diagnose. This article provides a summary of how to diagnose TIA accurately, using a focused history informed by cerebrovascular localization; how to triage, evaluate, and risk stratify patients; and how to implement preventative strategies.
Review of the Data
Classically, TIAs are defined as lasting less than 24 hours; however, 24 hours is an arbitrary number, and most TIAs last less than one hour.1 Furthermore, this definition has evolved with advances in neuroimaging that reveal that up to 50% of classically defined TIAs have evidence of infarct on MRI.1 There is no absolute temporal cut-off after which infarct is always seen on MRI, but longer duration of symptoms correlates with a higher likelihood of infarct. To reconcile these observations, a recently proposed definition stipulates that a true TIA lasts no more than one hour and does not show evidence of infarct on MRI.3
The causes of TIA are identical to those for ischemic stroke. Cerebral ischemia can result from an embolus, arterial thrombosis, or hypoperfusion due to arterial stenosis. Emboli can be cardiac, most commonly due to AF, or non-cardiac, stemming from a ruptured atherosclerotic plaque in the aortic arch, the carotid or vertebral artery, or an intracranial vessel. Atherosclerotic disease in the carotid arteries or intracranial vessels can also lead to thrombosis and occlusion or flow-related TIAs as a result of severe stenosis.
(click for larger image)Table 1. Signs and symptoms used to help localize vascular ischemia
Risk factors for TIA mirror those for heart disease. Non-modifiable risk factors include older age, black race, male sex, and family history of stroke. Modifiable factors include hypertension, hyperlipidemia, tobacco smoking, diabetes, and AF.4
Most of the time, patients’ symptoms will have resolved by the time they are evaluated by a physician. Therefore, the diagnosis of TIA relies almost exclusively on the patient history. Eliciting a good history helps physicians determine whether the episode of transient neurologic dysfunction was caused by cerebral ischemia, as opposed to another mechanism, such as migraine or seizure. This calls for a basic understanding of cerebrovascular anatomy (see Table 1).
Types of Ischemia
Anterior cerebral artery ischemia causes contralateral leg weakness because it supplies the medial frontal and parietal lobes, where the legs in the sensorimotor homunculus are represented. Middle cerebral artery (MCA) ischemia causes contralateral face and arm weakness out of proportion to leg weakness. Ischemia in Broca’s area of the brain, which is supplied by the left MCA, may also cause expressive aphasia. Transient monocular blindness is a TIA of the retina due to atheroemboli originating from the internal carotid artery. Vertebrobasilar TIA is less common than anterior circulation TIA and manifests with brainstem symptoms that include diplopia, dysarthria, dysphagia, vertigo, gait imbalance, and weakness. In general, language and motor symptoms are more specific for cerebral ischemia and therefore more worrisome for TIA than sensory symptoms.5