Transient ischemic attack

A transient ischemic attack (TIA) is a transient episode of neurologic dysfunction caused by ischemia (loss of blood flow) – either focal brain, spinal cord, or retinal – without acute infarction (tissue death). TIAs have the same underlying cause as strokes: a disruption of cerebral blood flow (CBF), and are often referred to as mini-strokes. Symptoms caused by a TIA resolve in 24 hours or less.^[1][2] TIA was originally defined clinically by the temporary nature of less than 24 hours of the associated neurologic symptoms. Recently, the American Heart Association and American Stroke Association (AHA/ASA) defined TIA as transient episode of neurologic dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction.^[1] TIAs cause the same symptoms associated with stroke, such as contralateral paralysis (opposite side of body from affected brain hemisphere) or sudden weakness or numbness. A TIA may cause sudden dimming or loss of vision (amaurosis fugax), aphasia, slurred speech (dysarthria) and mental confusion. But unlike a stroke, the symptoms of a TIA can resolve within a few minutes or within 24 hours. Brain injury may still occur in a TIA lasting only a few minutes. Having a TIA is a risk factor for eventually having a stroke or a silent stroke.^[1][3]

A silent stroke, also known as silent cerebral infarct (SCI), differs from a TIA in that there are no immediately observable symptoms. An SCI may still cause long lasting neurological dysfunction affecting such areas as mood, personality and cognition. An SCI often occurs before or after a TIA or major stroke.^[4]

A cerebral infarct that lasts longer than 24 hours but fewer than 72 hours is called a reversible ischemic neurologic deficit or RIND.

Signs and symptoms

Symptoms can vary widely across people, and across brain regions. The most frequent symptoms include temporary loss of vision (typically amaurosis fugax); difficulty speaking (aphasia); weakness on one side of the body (hemiparesis); and numbness or tingling (paresthesia), usually on one side of the body. Impairment of consciousness is very uncommon. There have been cases of temporary and partial paralysis affecting the face and tongue of the afflicted. The symptoms of a TIA are short-lived and usually last a few seconds to a few minutes; most symptoms disappear within 60 minutes. Some individuals may have a lingering feeling that something odd happened to the body. Dizziness, lack of coordination or poor balance are also symptoms related to TIA. Symptoms vary in severity.

Causes

The most common cause of a TIA is an embolus that occludes an artery in the brain. This usually arises from a dislodged atherosclerotic plaque in one of the carotid arteries (i.e. two of the four major arteries supplying the brain) or from the vertebral-basilar arteries. Another common cause is from a thrombus (i.e. a blood clot) that has originated from the (usually left) atrium of the heart due to atrial fibrillation. In a TIA, the blockage period is very short-lived and hence there is no permanent damage.^[5] The cholesterol build-up is gradual and eventually narrows the lumen. With time, blood flow to that side of the brain is reduced and a stroke may occur as a result. In other cases, cholesterol particles from the atherosclerotic plaque may suddenly break off and enter the brain. In some people, these fragments come off from the heart and go to the brain. This often happens during a heart attack or an infection of the valves. ^[6]

Other reasons include excessive narrowing of large vessels resulting from an atherosclerotic plaque and increased blood viscosity caused by some blood diseases. TIA is related to other medical conditions such as hypertension, heart disease (especially atrial fibrillation), migraine, hypercholesterolemia, and diabetes mellitus.

Risk factors

• Family history of stroke or TIA substantially increases risk.
• People 55 years or older are at higher risk.
• Males have a slightly higher risk of TIA than females.
• High blood pressure (hypertension, either primary or secondary)
• Diabetes mellitus
• Tobacco smoking

Diagnosis

TIA will usually be diagnosed after a doctor performs a history and a physical exam. There are several radiological tests that are done to evaluate patients who have had a TIA. These include a CT scan or an MRI of the brain, ultrasound of the neck, or an echocardiogram of the heart. In most cases, the source of atherosclerosis is usually identified with an ultrasound.^[7]

Differential diagnoses

Other diagnoses may have symptoms similar to those of a TIA:

1. Atypical migraine if visual symptoms occur such as the perception of wavy or jagged lines or tiny specks of light and if a headache occurs.^[8] Typically a history of prior migraines is present.
2. Partial seizure in the parietal area of the brain
3. Glucose abnormalities; these could be distinguished by a history of diabetes mellitus and a loss of consciousness
4. Electrolyte abnormalities
5. Hypertensive encephalopathy (headache, delirium, hypertension, cerebral edema)
6. Subdural hematoma (history of trauma, headache, loss of consciousness)
7. Brain tumor (mode of onset, progressive headaches, increased intracranial pressure)
8. Demyelinating disease
9. Conversion disorder

Prevention

A TIA may be prevented by changes in lifestyle; although most of these recommendations have no solid empirical data, most medical professionals believe them to be so.^[9] These include:

• Avoiding smoking
• Cutting down on fats to help reduce the amount of plaque build up
• Eating a healthy diet including plenty of fruit and vegetables
• Limiting sodium in the diet, thereby reducing blood pressure
• Exercising regularly
• Moderating intake of alcohol, stimulants, sympathomimetics, etc.
• Maintaining a healthy weight
• Controlling blood pressure and blood sugars

Treatment

The mainstay of the treatment following acute recovery from a TIA depends on the underlying cause. It is not always immediately possible to tell the difference between a CVA (stroke) and a TIA. Most patients who are diagnosed at a hospital's emergency department as having suffered from a TIA will be admitted to the hospital if it is their first TIA, for telemetry, blood pressure monitoring and other specific tests. If it is a second or subsequent TIA, most patients will be discharged home and advised to contact their primary physician to organize further investigations. A TIA is often the last warning before a CVA occurs. The cause of TIA should be immediately investigated by imaging of the brain. Occasionally, none of these tests will determine the cause, but the symptoms show that the stroke did occur. Actually, TIA is a form of stroke in nature.

To reduce the risk of recurrence, patients are recommended to undergo lifestyle changes including quitting smoking, losing weight, eating more fruit and vegetables, and exercising regularly.^[10][11]

Medication

Antiplatelet medications such as aspirin are generally recommended. They reduce the overall risk of recurrence by 13% with greater benefit early on.^[12] The initial treatment is aspirin, second-line is clopidogrel (Plavix), third-line is ticlopidine. If TIAs recur after aspirin treatment, the combination of aspirin and dipyridamole may be recommended. Some people may also be given modified-release dipyridamole or clopidogrel.

An electrocardiogram (ECG) may show atrial fibrillation, a common cause of TIAs, or other abnormal heart rhythms that may cause embolization to the brain. An echocardiogram is useful in detecting a blood clot within the heart chambers. Such people may benefit from anticoagulation medications such as heparin and warfarin.

Surgery

If the TIA affects an area that is supplied by the carotid arteries, an ultrasound (TCD) scan may demonstrate carotid stenosis. For people with a greater than 70% stenosis within the carotid artery, removal of atherosclerotic plaque by surgery, specifically a carotid endarterectomy, may be recommended. The blood vessel is opened up and the plaque is removed. The carotid may be replaced with a vessel retrieved from the lower leg or foot. The procedure is not technically difficult but carries the potential complication of inducing a stroke. A stroke can occur during surgery or after the procedure. The chance of a stroke ranges from 1–4 percent.^[13]

Prognosis

People diagnosed with TIA are sometimes said to have had a warning for an approaching stroke. If the time period of blood supply impairment lasts more than a few minutes, the nerve cells of that area of the brain die and cause permanent neurologic damage. One-third of the people with TIA later have recurrent TIAs and one-third have a stroke because of permanent nerve cell loss. Other sources cite that 10% of TIAs will develop a stroke within 90 days, half of which will occur in the first two days following the TIA.^[14] The risk of a stroke occurring after a TIA can be predicted using the ABCD² score. However the ABCD² score ironically does not reliably predict the level of carotid artery stenosis (thought to be a major cause of stroke)in TIA patients. Instead, a person's age is more reliable in predicting any level of carotid stenosis in either symptomatic or asymptomatic side in transient ischaemic attack. ^[15] Response to aspirin treatment and prognosis in people with TIA could be predicted using emerging new blood tests. ^[16]

References