Transient ischemic attack: Omen and opportunity
ABSTRACTA transient ischemic attack (TIA) is not a benign event; it is often the precursor of stroke. As such, every TIA deserves to be taken seriously, and patients who present with a TIA should be promptly evaluated and, if appropriate, started on stroke-preventive therapy.
KEY POINTS
- Modifiable risk factors for stroke and TIA include cigarette smoking, hypertension, diabetes, lipid abnormalities, atrial fibrillation, carotid stenosis, and dietary and hormonal factors.
- The three major mechanisms of stroke and TIA are thrombosis, embolism, and decreased systemic perfusion.
- Typical symptoms of TIA include hemiparesis, hemisensory loss, aphasia, vision loss, ataxia, and diplopia. Three clinical features that suggest TIA are rapid onset of symptoms, no history of similar episodes in the past, and the absence of nonspecific symptoms.
- In suspected TIA, magnetic resonance imaging is clearly superior to noncontrast computed tomography (CT) for detecting small areas of ischemia; this test should be used unless contraindicated.
- Imaging studies of the blood vessels include CT angiography, magnetic resonance angiography, conventional angiography, and extracranial and transcranial ultrasonography.
ASSESSING RISK OF STROKE AFTER TIA
There is a practical need for prediction of stroke during the first few days after the event. The ABCD and ABCD2 scores were developed to stratify the short-term risk of stroke in patients with recent TIA.
The ABCD score
The ABCD score53 was derived to allow primary care physicians and other physicians to identify which patients with a suspected diagnosis of TIA should be referred for emergency assessment, to allow secondary-care physicians to determine which patients with probable or definite TIA need emergency investigation and treatment, to allow public education about the need for medical attention after a TIA, and to identify people at high risk.
The ABCD2 score
The ABCD2 score predicts the short-term risk of stroke following a TIA.54 Points are assigned as follows:
- Age > 60 years: 1 point
- Blood pressure (systolic) > 140 mm Hg or diastolic blood pressure > 90 mm Hg: 1 point
- Clinical factors: unilateral weakness with or without speech impairment: 2 points (1 point for speech impairment without weakness)
- Duration of symptoms > 60 minutes: 2 points (1 point for 10–59 minutes)
- Diabetes: 1 point.
Thus, the possible total ranges from 0 to 7 points. Higher scores indicate a greater risk of stroke at 2, 7, 30, and 90 days:
- Total score 0, 1, 2, or 3: 2-day stroke risk 1.0% (low risk)
- Total score 4 or 5: 2-day stroke risk 4.1% (moderate risk)
- Total score 6 or 7: 2-day stroke risk 8.1% (high risk).
WHO SHOULD BE HOSPITALIZED?
It has been suggested that the ABCD2 score can help in triaging patients to hospital admission or outpatient care, though no randomized trial has actually evaluated the utility of the ABCD2 score in this way.3
A study of consecutive TIA patients admitted over 12 months55 found that patients with an ABCD2 score of 3 or less had the same chance of requiring hospitalization (based on positive diffusion-weighted MRI studies, risk factor identification, and treatment initiation) as those with a score of 4 to 7. Hence, admitting TIA patients on the basis of the ABCD2 score alone requires further study. However, such decisions, though informed by clinical data, depend heavily on societal input (eg, from insurance companies, national health protocols) and may be outside the purview of clinical investigation.
The benefits of hospitalization include the ability to rapidly carry out tests such as cardiac monitoring for atrial fibrillation; to detect atherosclerosis, aortic arch atheroma, and paradoxical emboli; and to quickly start secondary prevention treatments and education about the importance of adhering to them. Early endarterectomy in the case of carotid stenosis can be offered. Additionally, if stroke symptoms recur, thrombolytic drug therapy can be started quickly.
Nguyen-Huynh et al56 analyzed the cost utility of 24-hour hospitalization for patients diagnosed with a recent TIA who were candidates for tissue plasminogen activator if a stroke occurred. They found hospitalization to be borderline cost-effective on the whole, with definite cost-effectiveness found in patients with higher stroke risk.
If patients come to medical attention several days after the TIA, then assessing risk with the ABCD2 score may no longer be reliable.57
INVESTIGATIONS
Parenchymal neuroimaging
Computed tomography (CT) without contrast is the most widely used neuroimaging test in the acute setting, since it is widely available, fast, and relatively low-cost. It will not show any abnormality in TIA or early ischemic stroke. However, it is helpful as a screening tool to rule out intracranial lesions such as hemorrhage or tumor. It may also show evidence of established infarction, which would indicate that the ischemia probably had been present for at least 6 to 12 hours.
MRI is clearly superior to noncontrast CT for detecting small areas of ischemia in patients with TIA, and it should be used unless the patient has a contraindication to it. Roughly one-third of TIA patients have lesions detectable on diffusion-weighted imaging, which helps to confirm that the episode was caused by cerebral ischemia, but nearly half of the diffusion MRI changes may be fully reversible.58 Evidence of prior stroke, leukoaraiosis, or white matter disease on fluid-attenuated inversion recovery and T2 sequences and microhemorrhages (on gradient echo sequences) help to determine a mechanistic diagnosis.
Subcategorizing TIA patients on the basis of the findings on diffusion-weighted MRI and the ABCD2 score is prognostically helpful.59 It can help to determine which patients need hospitalization and aggressive treatment, and in the case of identified diffusion-weighted MRI-positive stroke, it helps to localize and elucidate the mechanism of stroke. Hence, MRI is the preferred neuroimaging study for evaluating patients with TIA.3
Vascular imaging
Establishing the status of both intracranial and extracranial vessels is important for understanding the etiology, estimating the risk of future ischemic events, and formulating a treatment plan—eg, carotid endarterectomy in cases of significant stenosis (70% to 99%), which reduces the risk of ipsilateral stroke.60 Imaging studies include CT angiography, magnetic resonance angiography, extracranial and transcranial ultrasonography, and conventional catheter-based angiography.
CT angiography has higher spatial resolution, but vessels may be obscured by calcification associated with atherosclerotic plaque. It has the advantage of wide availability, low cost, short scanning time, and excellent patient tolerability.
Magnetic resonance angiography with gadolinium enhancement offers good quality imaging from the great vessels in the chest to the medium-sized vessels distal to the circle of Willis.
The contrast agents used in MRI and CT can have negative consequences in patients with renal disease. MRI contrast has been associated with nephrogenic fibrosing dermopathy, 61 and CT contrast can cause contrast-induced nephropathy.62
Carotid ultrasonography and transcranial Doppler ultrasonography are noninvasive and are not associated with significant adverse events. They can be used safely in patients with renal dysfunction, and they provide physiologic information that cannot be obtained with MRI and CT, which are static imaging techniques. Detecting microemboli on transcranial Doppler is an independent predictor of recurrent ischemic events.63,64
Catheter-based angiography is occasionally needed in confusing or more complicated cases, but it is invasive and occasionally is associated with iatrogenic stroke and other vascular complications.
Cardiac and aortic imaging
Echocardiography is used to detect lesions that can be sources of embolism such as regional wall-motion abnormalities, cardiac thrombus or mass, endocarditis, aortic arch atheroma, and patent foramen ovale. In patients with cryptogenic TIA or stroke, those with patent foramen ovale alone were found to have a lower risk of recurrent stroke than those who had both atrial septal aneurysm and patent foramen ovale.65
Transesophageal echocardiography is more sensitive than transthoracic echocardiography for detecting cardioembolic lesions, especially patent foramen ovale.66 In patients with cerebral ischemia and normal transthoracic findings, cardiac sources of embolism may be detected in about 40% of patients with transesophageal echocardiography.67
Cardiac rhythm monitoring
Electrocardiography and prolonged telemetry are recommended in patients with cryptogenic TIA to detect cardiac ischemia and paroxysmal atrial fibrillation. In one study, Holter monitoring detected atrial fibrillation in 6% of patients hospitalized with ischemic stroke or TIA.68 In another study, atrial fibrillation was detected after a median of 21 days of outpatient cardiac monitoring in 23% of patients.69
The optimal duration of outpatient telemetry has not yet been established, but studies have found significant increases in detection of paroxysms of atrial fibrillation with monitoring for 7 or longer.70
Laboratory tests in the acute setting
These include lipid profile, hemoglobin A1c, and cardiac enzymes. The advantages of hospitalization are early detection of these modifiable risk factors and early initiation of treatment.
Tests for rarer disorders
Tests for rarer disorders are sometimes indicated in unusual cases, such as ischemic symptoms occurring in young patients without other common risk factors. This includes testing for prothrombotic states, toxicology, blood cultures, inflammatory markers, hemoglobin electrophoresis, and lumbar puncture. The benefit of routine testing for thrombophilic disorders in cerebrovascular disease remains uncertain, with no clear association demonstrated with arterial stroke, but testing is more relevant in the case of venous (and paradoxical) thromboembolism.71
