Monday, August 11, 2008
Transient Ischemic AttackWhat is a transient ischemic attack (TIA)?
The primary role of the brain is to send signals to the body for motor function and through the five senses (sight, hearing, touch, smell, and taste), to receive signals and return the appropriate response. The brain processes information through conscious thought and unconsciously through nerve systems that control basic bodily functions, like heart rate, temperature control and balance.
For the most part, the brain is arranged so that the right side of the brain controls the left side of the body and the left side of the brain controls the right of the body. Vision is located in the back of the brain (occiput) and balance and coordination is located at the bottom of the brain (cerebellum). Blood supply to the brain comes from the carotid arteries that are located in the front of the neck and the vertebral arteries that run in the back of neck through small canals in the bony spine (vertebrae) of the neck.
When a portion of the brain loses its blood supply, it becomes oxygen deficient and can become damaged. The part of the body that the brain controls stops functioning. This is called a stroke or a cerebro-vascular accident (CVA). If the brain is able to regain its blood supply quickly, then the CVA symptoms may resolve; this is known as a transient ischemic attack (TIA).
What are the causes of transient ischemic attack (TIA)?
Loss of blood supply to portions of the brain can occur for a variety of reasons. A blood vessel can get blocked and blood supply to a part of the brain is lost, or a blood vessel leaks blood into the brain (brain hemorrhage). Most commonly, the blood vessel is blocked. The blockage can be caused by a blood clot that forms in the blood vessel (thrombosis) or it can be caused by a clot or debris that floats downstream (embolus).
Atherosclerosis or "hardening of the arteries" can cause fatty plaque formations in he blood vessel wall. The plaque can rupture and causes a small blood clot to form and occlude the blood vessel. Blockage can also occur when debris from narrowing of a carotid artery breaks off, and floats downstream to cause the occlusion. Sometimes, in people with an irregular heart beat called atrial fibrillation, small blood clots can be formed and travel to the brain to cause the obstruction.
Picture of Carotid Artery Disease and Plaque Buildup
Brain hemorrhage or bleeding in the brain can be due to an aneurysm, a weak spot in a blood vessel that ruptures and spills blood into the brain tissue, or it may be due to spontaneous bleeding caused by poorly controlled hypertension (high blood pressure). Such bleeding more commonly results in a true stroke (CVA), as opposed to a TIA.
What are the risk factors for transient ischemic attack (TIA)?
The risk factors for TIA or stroke are the same as those for other vascular disease, similar to heart attack (coronary artery disease) or peripheral vascular disease which causes decreased blood flow to the legs. Aside from family history, other risk factors that the patient can influence include:
smoking,
high blood pressure,
high cholesterol, and
diabetes.
Also, any condition that results in stagnant blood flow and or clotting may result in a TIA due to embolization of a blood clot. Such conditions may include atrial fibrillation, large heart attacks, and severe weakness of the heart muscle.
What are the symptoms of transient ischemic attack (TIA)?
The intensity and location of the blood limitation to the brain will determine what symptoms will present as a result of a stroke or TIA. Many people present with confusion, weakness, and lethargy. If the loss of blood supply is in an area supplied by the carotid arteries, a classic presentation may include weakness or paralysis and numbness of one side of the body. The whole side may be affected, or just one limb. Often there is a facial droop. If the stroke is on the left side of the body where the speech centers are located, there may be difficulty understanding words or speaking. Partial vision loss may also be part of the constellation of symptoms.
Strokes involving the vertebral arteries decrease blood supply to the base of the brain and may cause a drop attack (a sudden fall while walking or standing, and then a quick recovery), an unexpected collapse, incoordination or difficulty walking.
The important distinction between stroke and TIA is resolution of the symptoms. By definition, the symptoms of a TIA must completely resolve. And, while this most often occurs within the first few minutes after symptom onset, it may take up to 24 hours to have complete return to normal.
A special type of TIA is amaurosis fugax. Transient blindness in one eye occurs because debris from a narrowed carotid artery clogs the artery (ophthalmic artery) that supplies blood to the back of the eye.
How is transient ischemic attack (TIA) diagnosed?
TIA is diagnosed by history and physical examination. Since most often the symptoms have resolved, the physician will need to take a good history from the patient and family or friends who witnessed the event. The physical exam will include careful attention to the neurologic examination. This may include:
Assess mental status to make certain the patient is alert and oriented.
Check eye range of motion and facial movement to evaluate the cranial nerves (the short nerves that run from the brain to the face and neck).
Listen to the neck with a stethoscope to detect abnormal sounds that may signal narrowing of the blood vessel (carotid bruits).
Check for a regular heart rhythm to rule out the presence of atrial fibrillation.
Examine the arms and legs for tone, power, and sensation.
Check coordination and balance.
If the diagnosis of TIA is made, further urgent testing is usually recommended, including:
Electrocardiogram (EKG) to confirm a regular heart rate
Computerized tomography (CT scan) of the brain to look for bleeding
Carotid ultrasound to look for narrowing of the large blood vessels in the neck
Routine blood tests may include a complete blood count (CBC) to look for anemia or low red blood cell count or too few platelets (thrombocytopenia). If the patient takes warfarin (Coumadin), a blood thinner, then an international normalized ratio (INR - a blood test that measures the degree of blood thinning) or prothrombin time (PT), may be performed to assess blood clotting measurements.
If there is concern that the heart is the source of blood clot or debris, then an echocardiogram or sound wave tracing of the heart may be considered.
What is the treatment for a transient ischemic attack (TIA)?
TIA Therapy
Treatment for a transient ischemic attack is aimed at preventing a second stroke. Since there is no way of determining the severity of future episodes and no guarantee that the symptoms will resolve, prevention of a future TIA or CVA is crucial.
Treatment guidelines address a variety of targeted goals.
Anti-platelet therapy
If the patient was not taking aspirin when the TIA occurred, it needs to be started (325mg per day).
If the patient was taking aspirin, then another anti-platelet drug called dipyridamole needs to be added. Aggrenox is a combination of aspirin and dipyridamole.
If the patient cannot tolerate aspirin, then clopidogrel (Plavix) should be used.
High blood pressure therapy
Even if the patient does not have hypertension or high blood pressure, there may be benefit in taking anti–hypertensive medications.
Two classes of drugs are recommended to be started at the same time, a diuretic and an ACE inhibitor.
The goal for normal blood pressure is 120/80.
Cholesterol lowering therapy
Guidelines recommend that a statin drug be started, even if cholesterol levels are normal.
Risk modification
Smoking, excessive alcohol, obesity and lack of physical activity are considered risks for future stroke. The following recommendations are now suggested:
Smoking: Counseling, smoking cessation aids like nicotine gum or medications like varenicline (Chantix) should be considered. Environmental smoke should be avoided.
Alcohol: Intake should be limited to two or fewer drinks a day for men and one or less for women.
Obesity: Overweight people should try to lose weight using a combination of diet, exercise and counseling. The goal is a BMI of 18.5-24.9 and a waist line of 35 inches or less for women and 40 inches or less for men.
Exercise: 30minutes of moderate exercise daily is recommended for those who are able. For patients with disabilities, a tailored exercise program to their capabilities should be arranged.
What is the prognosis for transient ischemic attack (TIA)?
A transient ischemic attack should be considered a major warning sign of an impending future stroke. Up to 10% of people will experience a stroke within three months of TIA. Since there is no way of predicting whether the next episode will resolve, the patient needs to be educated - that should symptoms occur, they need to access medical care immediately. Activating the emergency medical Services system and calling 911 is recommended.
If a stroke occurs, there is a very short period of time where thrombolytic (clot dissolving) drugs, [for example, alteplase (TPA)], can be used to reverse a stroke. In most hospitals, the drug can only be given within three hours of onset of stroke symptoms. In that three hours, the patient needs to get to the hospital, the diagnosis needs to be made, laboratory tests and head CT scans need to be performed, neurologic consultation needs to occur, and the drug administered. The longer the delay, there is a higher the risk that the drug won't work and that complications like bleeding into the brain will occur.
Specialized interventional radiologists can inject TPA directly into the clot that has blocked the blood vessel in the brain. This can extend the time frame to six hours, but currently this treatment is not widely available.
TIAs should be considered the equivalent of angina of the brain. In heart disease, angina is the heart pain that warns of potential heart attack. When heart muscle is damaged, it cannot be replaced or repaired. Similarly, brain tissue is at risk when there is decreasePrognosis
Patients diagnosed with a 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 deficit. One third of the people with TIA later have recurrent TIAs and one third have a stroke due to permanent nerve cell loss.
The ABCD2 score can predict likelihood of subsequent stroke.[2][3]
The score is calculated as:
• Age ≥ 60 years = 1 point
• Blood pressure at presentation ≥ 140/90 mm Hg = 1 point
• Clinical features
unilateral weakness = 2 points
speech disturbance without weakness = 1 point
• Duration of attack
≥ 60 minutes = 2 points
10–59 minutes = 1 point
• Diabetes = 1 point
Interpretation of score, the risk for stroke:
• Score 0-3 (low)
o 2 day risk = 1.0%
o 7 day risk = 1.2%
• Score 4-5 (moderate)
o 2 day risk = 4.1%
o 7 day risk = 5.9%
• Score 6–7 (high)
o 2 day risk = 8.1%
o 7 day risk = 11.7%
d blood supply and it, too, cannot be replaced.
Labels: NEUROLOGY
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