Diagnosing Transient Ischemic Attacks (TIAs) and Determining Risk for Stroke

In people who experience transient ischemic attacks or small strokes, it is important to determine the source of these attacks in order to prevent a major stroke. A complete blood count, chest x-ray, and electrocardiogram are usually performed. Discouragingly, a 2001 study reported that over 30% of patients with TIA who called their primary care physician were neither evaluated nor sent to the hospital within the month after a first event.

Examining the Carotid Artery. The physician usually first examines the carotid artery to determine if it is severely narrowed. If it is, the patient is in danger of a major stroke. (The thickness of carotid artery is also proving to be a valuable indicator for long-term risks for stroke, as well as heart disease and mortality rates in general.)

The physician may use a number of approaches to determine the thickness of the artery:

 
• A clue to a blocked carotid artery is a bruit. This is a whooshing sound caused by blood flow turbulence in the narrowed artery. A physician may be able to hear a bruit using a stethoscope. Occasionally, even a patient can hear the sound. The presence of a bruit, however, is not necessarily a sign of an impending stroke, nor does the absence of a bruit indicate an unblocked artery.  
• Carotid ultrasound is a very valuable tool for measuring the width of the artery. At this time, ultrasound is most useful in people between the ages of 40 and 60 years. It should be noted that severely blocked carotid arteries may distort some measurements, so other tests may be required to confirm the results.  
• The blood pressure to the eye may also be measured. If blood flow to the eye is reduced, the physician estimates that the carotid artery is probably severely narrowed.

Other Imaging Techniques. Other imaging techniques may be useful for identifying small clots or other indicators of risk in the brain.

 
• Transcranial duplex sonography is an ultrasound technique that can identify tiny clots in the brain that do not produce symptoms but place patients at higher risk for TIAs or Stroke. In one study, the use of this technique to identify blockage in large arteries in the brain was very helpful in predicting the outlook for patients who had experienc ed an ischemic stroke. It may eventually prove to be useful in identifying unruptured aneurysms.  
• A Magnetic Resonance Imaging (MRI) scan is an accurate way of evaluating the blood vessels and the brain’s circulation. This technique can even identify silent brain injuries in elderly patients with neurologic impairment but no symptoms of stroke, but it is very expensive and not routinely used.

Researchers are hoping that advanced imaging techniques may help doctors to predict outlook in stroke patients.

Cerebral Angiography. If less invasive tests indicate a need for surgery, cerebral angiography may be used. (This procedure can also detect aneurysms.) This requires the insertion of a catheter into the groin, which is then threaded up through the arteries to the base of the carotid artery. At this point a dye is injected and x-rays are taken to determine the location and extent of the narrowing, or stenosis, of the artery. It should be noted that the risk of stroke itself increases using this technique, particularly in elderly people with diabetes.

Diagnosing a Major Stroke
To save a patient’s life, a fast diagnosis of both the presence and type of stroke is critical. The first step is to determine whether symptoms actually indicate a stroke. (Simple verbal and physical tests enable emergency teams to identify nearly all stroke patients.) Noninvasive techniques for diagnosing transient ischemic attacks are also used for major strokes.

Determining the Type and Cause of a Stroke. Once a stroke has been determined, the next important step is to determine as quickly as possible whether it is hemorrhagic or ischemic. Clot-busting drug therapies can be life-saving for ischemic stroke patients, but they are effective only in the first three hours. In addition, they cause bleeding and can be lethal if the stroke is actually caused by a hemorrhage. One or more of the following diagnostic tools may be used:

 
• A computed tomography (CT) scan performed early on is essential in ruling out Hemorrhagic stroke. It is accurate for diagnosing about 95% of Hemorrhagic strokes. Evidence of ischemic stroke will usually not show up on a CT scan until after a few days. (The ultrasound technique, transcranial duplex sonography, may be sensitive enough to differentiate between hemorrhagic and ischemic strokes if CT scans are not available.)  
• If the CT scan is negative, but the physician still suspects a Hemorrhagic stroke, a spinal tap may be indicated. Spinal fluid containing significant amounts of blood will usually confirm a Hemorrhagic stroke.  
• A heart evaluation using an electrocardiogram (a test that records the electrical current in the heart muscle) and usually an echocardiogram (a machine that uses ultrasound to create an image of the chambers and valves of the heart) is always done when an ischemic stroke is suspected. A technique called transesophageal echocardiography is particularly useful for determining causes, such as atrial fibrillation, that in turn lend themselves to targeted treatments.

Blood Tests
A number of blood tests may be helpful for predicting the risk for a stroke as well determining the severity and complications of an existing stroke. Some of these are investigatory.

 
• Some blood tests are used to determine clotting times.  
• Blood sugar levelss (hyperglycemia)  are measured. Elevated levels indicate a worse outcome for some strokes (although not hemorrhagic or lacunar strokes).  
• One blood test measures glutamate, an amino acid. High levels indicate a severe stroke.  
• The inflammatory response in the brain stimulates the release of certain markers that are used to diagnose a stroke. C-reactive protein, enzymes called troponins, and elevated erythrocyte sedimentation rates (ESR) are also indicators of the inflammatory process and may predict a higher risk for stroke and a poorer outcome in people with existing stroke.  
• Elevated levels of lipoprotein (a) may reveal the possibility of an unruptured aneurysm, which can be confirmed with an MRI ( magnetic resonance imaging).