Diagnosis
Preventing a major stroke in people who experience transient ischemic attacks or small strokes requires determining the source of such attacks. 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 doctor were neither evaluated nor sent to the hospital within the month after a first event.
Examining the Carotid Artery. The doctor examines the carotid artery to determine if it is severely narrowed. If so, the patient is in danger of a major stroke. (The thickness of the carotid artery is also an important indicator for long-term risks for stroke, as well as heart disease and mortality rates in general.)
The doctor may use a number of approaches to determine the thickness of the artery:
- An important clue to a blocked carotid artery is a bruit. This is a whooshing sound caused by blood flow turbulence in the narrowed artery. A doctor 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. Severely blocked carotid arteries may distort some measurements, so other tests may be required to confirm the results.
- Measuring blood pressure to the eye may also be important in identifying problems in the carotid artery. If blood flow to the eye is reduced, it is likely that the carotid artery is severely narrowed.
Imaging Techniques for TIAs. Several imaging techniques may identify small clots or other indicators of risk in the brain.
General Guidelines for Diagnosing a Major Stroke
Identifying a Stroke Quickly. To save a patient's life, a fast diagnosis of both the presence and type of stroke is critical. Health professionals have devised different tests to help emergency workers quickly identify a person with stroke even before they reach the hospital. For example, an assessment tool called the Face, Arm, Speech Test (FAST) is highly accurate. It involves watching for the following signs:
- Face: The face is not symmetrical. The mouth droops, and the patient is unable to show teeth when smiling.
- Arm: The patient is unable to lift an arm above shoulder level.
- Speech: The patient has trouble talking clearly and following simple instructions.
In one study, emergency workers who used this test accurately identified more people with stroke than either primary care or emergency room doctors.
Determining Ischemia Versus Hemorrhagic Stroke. Once a stroke has been identified, 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 3 hours. In addition, they cause bleeding and can be lethal if the stroke is caused by a hemorrhage.
A computed tomography (CT) scan is essential for identifying or ruling out hemorrhagic strokes. The goal is to complete the CT examination and obtain and interpret the results within 45 minutes of arrival at the hospital. (An ultrasound technique called transcranial duplex sonography may be sensitive enough to differentiate between hemorrhagic and ischemic strokes if CT scans are not available.)
Certain factors suggest a hemorrhagic rather than ischemic stroke. They include specific symptoms (coma, vomiting, and severe headache), taking anticoagulants, very high systolic blood pressure, or high blood sugar levels in nondiabetics. However, such findings are not conclusive, and a CT scan or MRI is always needed.
Ruling Out Other Disorders. In most cases of stroke, the diagnosis is evident although a number of conditions may cause similar symptoms. These include seizures, infections that cause mental confusion, syncope (fainting), hypoglycemia, and brain tumors.
Imaging Tests Used for Stroke and Risk Factors for Stroke
Computed Tomography. A computed tomography (CT) scan is the standard imaging test for the brain. The test is performed as early as possible. It is essential in ruling out hemorrhagic stroke and can accurately diagnose about 95% of hemorrhagic strokes. The full evidence of an ischemic stroke will usually not show up on a CT scan for hours to days. A CT scan, however, may be useful in identifying early signs of injury from ischemic strokes that could effect the decision to use thrombolytics (clot-busting drugs). High-speed CT scans (called helical or spiral CTs), which quickly identify ischemic strokes and the location of the blockage, are now available in many centers.
Magnetic Resonance Imaging (MRI). A standard magnetic resonance imaging (MRI) scan is able to evaluate the blood vessels and the brain's circulation and determine injuries from ischemic strokes. It is not very useful in the first hours of a stroke, however, since it tends to show abnormalities that may not be significant. Advanced MRI techniques, such as diffusion- or perfusion-weighted MRIs, may be sensitive enough to identify injured areas within minutes of symptoms. MRIs cannot be used by patients with pacemakers or metal implants, or who are claustrophobic.
Ultrasound. Ultrasound may be used in different circumstances. This imaging technique is painless and noninvasive.
- Carotid ultrasound (also called Doppler or duplex sonography) can determine blockage in the carotid arteries that could lead to or be causing a stroke.
- Transcranial duplex sonography can identify blockage in large arteries in stroke patients and to monitor the effects of thrombolytic therapy.
- Cerebral Angiography. Cerebral angiography is an invasive procedure that may be used for patients with TIAs who require surgery. It can also detect aneurysms and monitor thrombolytic therapy. It 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, CTs, or MRI scans determine the location and extent of the narrowing, or stenosis, of the artery. In people with TIAs the risk of stroke itself increases using this technique, particularly in elderly people with diabetes.
Other Techniques. Other imaging tests, including positron-emission tomography (PET) and single photon-emission computed tomography (SPECT), may also help the doctor identify injuries caused by the stroke.
Heart Evaluation
Electrocardiogram (ECG). A heart evaluation using an electrocardiogram (ECG) is important in any patient with a stroke or suspected stroke. An ECG records the electrical current in the heart muscle.
Echocardiogram. An echocardiogram uses ultrasound to view the chambers and valves of the heart. It is generally useful for stroke patients to identify blood clots or risk factors for blood clots that can travel to the brain and cause stroke. There two are types:
- Transthoracic echocardiograms (TTE) view the heart through the chest. It is noninvasive and is the standard approach.
- Transesophageal echocardiogram (TEE) examines the heart using an ultrasound tube that the patient literally swallows and passes down the throat. It is uncomfortable and requires sedation. It is typically used to obtain more accurate images of the heart if a TTE has suggested abnormalities, such as atrial fibrillation or patent foramen ovale (PFO).
Other Tests
Blood Tests. Several blood tests may help predict the risk for a stroke and determine the severity and complications of an existing stroke.
- Specific blood tests are important to determine clotting times, to check electrolytes (potassium, calcium, sodium), and to measure factors indicating liver or kidney problems. Kidney tests measure blood proteins that are filtered through the kidneys. These proteins include creatinine and blood urea nitrogen (BUN). A more recent type of kidney test measures the protein cystatin C. Recent research suggests that the cystatin C kidney test may be better at predicting cardiovascular risks in elderly patients.
- Blood sugar (glucose) levels are measured. Hyperglycemia (high levels) may indicate a worse outcome for some strokes (although not hemorrhagic or lacunar strokes). Hypoglycemia (low levels) is a common complication of diabetes treatments, and its symptoms may mimic those of a stroke.
- A new blood test, the PLAC test, was approved in 2005 to help diagnose people at increased risk for ischemic stroke. The PLAC test measures an enzyme called lipoprotein-associated phospholipase A2 (Lp-PLA2). Patients with high levels of this protein have twice the risk for ischemic stroke as patients with normal levels.
Examination of Spinal Fluid. If the CT scan is negative but the doctor still suspects a subarachnoid hemorrhagic stroke, a spinal tap may be performed. Spinal fluid containing significant amounts of blood will usually confirm a hemorrhagic stroke.
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