This test involves the use of a needle to obtain cerebrospinal fluid (CSF) from a fluid-filled sac in the back. This sac surrounds the entire spinal cord and extends from the bottom of your spine all the way up to the brain. When you have a spinal fluid examination, you will be asked to sign an informed consent. The reason for this is so that you understand that there are some minor risks to the procedure, such as a little bit of localized bleeding, a small possibility of skin infection, a little bit of tingling or pain if the needle that is used happens to bump up against one of the nerves in your back, and headache. Of these possible side effects, headache is by far the most common. About one or two out of every ten people who have a spinal fluid examination will experience a CSF drainage headache.
After you sign the informed consent, you will be asked to either sit or lie down on an examining table. You will bring your knees up close to your abdomen to open the bones in your back and make it easier for the needle to pass into the space containing spinal fluid. Your doctor will scrub your back with an iodine solution, or alcohol if you are allergic to iodine. Your skin will be numbed with xylocaine, and a needle will be inserted into the appropriate place in your back. Unfortunately, sometimes it is not possible to obtain spinal fluid. Problems can sometimes arise in patients who are overweight, or who have a crooked spine. In these circumstances, spinal fluid can be obtained with the help of a radiologist. The entire procedure usually takes less than one-half hour. After the procedure is over, you are usually asked to lie flat on your back for twenty or thirty minutes to provide some time for the spinal fluid to replenish itself in your system. After the procedure, you should drink plenty of fluids, and lie down if you develop a headache upon sitting or standing. This occurs when fluid continues to leak out of the sac through the needle hole. The pain increases when you stand or sit up, and is relieved by lying down flat. With time, the hole usually seals itself, within a few days in most cases. Rarely, a procedure called a blood patch is necessary to seal the hole. If the headache persists, you should notify the office, so that we can determine whether you might need a blood patch.
Contrary to popular myth, the spinal fluid examination is very safe. It is extremely rare for any serious complication to develop after a spinal fluid examination. In over fifteen years as a physician, I have never seen a serious complication from a spinal fluid examination. The test can be very useful to identify the presence of infection, such as in meningitis, to determine whether spinal fluid pressure is elevated as in pseudotumor cerebri, and to establish the presence of immunoglobulins that attack the nervous system, as in multiple sclerosis. These and several other conditions are among the many indications for a spinal fluid examination.
You have thirty-one pairs of peripheral nerves. These nerves come off the spinal cord to provide sensory and motor functioning in all parts of your body except those handled by cranial nerves. The PNCV test includes many types of electrical measurements of your nerves and muscles. While all of the specific subtypes of the PNCV examination will not be discussed (for example, we do not discuss the H-reflex, F-wave, and blink reflex), the basic method is as follows. A sensory or motor nerve is stimulated, and a response is recorded from either a muscle or a nerve. By measuring the distance between the stimulation and recording sites, and the time that it takes the electrical impulse to travel from one place to the next, one can determine Òconduction velocityÓ for both sensory and motor nerves. The size of the response is also recorded, a compound muscle action potential in the case of motor nerves, and a sensory nerve action potential (SNAP amplitude), in the case of sensory nerves. There are normal values established for sensory and motor nerves for amplitude, latency, conduction velocity, and other parameters. By performing these tests, your doctor can learn many important things about your nerve and muscle function. A special type of PNCV test is the repetitive nerve stimulation test. This test involves rapidly stimulating the nerve and generating a rapid succession of muscle twitches. In certain types of disorders, that affect the connection between the nerves and muscles, (the neuromuscular junction), there is a change in the response seen from the muscle when the first and last responses in a “train” of a dozen or so stimulations (3 per second) are compared. This test can be helpful to confirm a diagnosis of myasthenia gravis, for example.
There are really no risks to the PNCV examination. The test is a little bit uncomfortable, but it is not dangerous. The discomfort does not linger, and lasts only a few seconds. The information obtained can be extremely valuable in identifying treatable kinds of disorders that may affect the nerve or muscle, or the neuromuscular junction. Sometimes it is necessary to test all four limbs, but it is usually sufficient to check only one or two. We use a skilled technician to perform this test, but our neurologists are also trained and qualified to perform and interpret the repetitive nerve stimulation test.
The EMG is an important counterpart to the PNCV test. The test involves the use of a needle to record electrical activity from within the muscle. Several muscles may need to be checked. Muscles in one to four limbs, along the spine, and even in the head or trunk may all need to be checked. Sometimes the tongue muscle needs to be checked. Rarely, the muscles near the anus might need to be checked. The EMG can provide critical information about whether there has been permanent disconnection between nerve fibers and the muscles they normally would supply. In addition, sick muscles, such as those found in muscular dystrophy, myositis, or a number of other muscle diseases, may produce electrical disturbances within the muscle that have a characteristic pattern or signature. Thus, the EMG is a valuable diagnostic test for muscle disease as well as nerve disease. The only potential risks of the EMG are pain from the needle insertion, and a small amount of bleeding that may occur, particularly if you are taking blood thinners of any type. Only full anticoagulation (e.g., with Heparin or Coumadin) is sufficiently concerning to potentially prevent you from having this test. During the test, you will simply lie on an examining table and try to relax. You may be asked to flex a muscle while the needle is inside your muscle. The test may take only 30 to 40 minutes, or it could take two hours, depending on the complexity and number of muscles that must be checked. There are no special preparations for an EMG or a PNCV test, other than removing any clothing that might limit access to the appropriate nerves and muscles.
The EEG is a recording of electrical activity within the brain. The major uses of EEG include detection of seizure activity and evaluation of other disorders that affect mental and neurological functioning. Episodes or spells are often evaluated with EEG to determine whether seizures are responsible for the spells. The recording may take place over the course of 30 to 60 minutes. In some cases, even more extensive and lengthy recordings may need to be obtained. Typically, a set of approximately 20 electrodes is placed in a standard fashion over the scalp. The electrical activity from these electrodes is recorded and compared so that the location of potential seizure activity or electrical abnormality can be identified.
The EEG is a noninvasive and safe test. It is possible that you could have a seizure during the EEG, because activation procedures are often utilized in an attempt to provoke a seizure. For example, you may be asked to hyperventilate, flashing lights may be used to stimulate your brain, and you will be encouraged to fall asleep during the EEG. All three of these procedures can increase your odds of having a seizure during the EEG. This is a good thing, because capturing the abnormal brain electrical activity helps confirm your diagnosis, and helps to locate the source of the seizure.
Ambulatory or “24-hour” EEG monitoring is accomplished when you wear the EEG device and electrodes so that brain electrical activity is continuously monitored while you go about your normal daily routine. The device can be taken home, and then returned a day or two later.
Another type of prolonged monitoring, called video-EEG, includes continuous videotaping of everything you do at the same time that brain electrical activity is recorded by EEG. This requires a short stay in the hospital. You may be asked to stay for as short as 24 hours, or as long as one week, depending on how many spells we are able to capture during your hospital stay. The more seizures we are able to capture, the shorter your hospital stay.
Some patients with seizures that do not respond to anticonvulsant medications may be candidates for an even more extensive type of prolonged video-EEG monitoring that is useful for planning possible surgical treatments for epilepsy. Such pre-surgical video-EEG recordings can continue for a week or longer, and may also involve the use of surgically implanted electrodes to record the seizure activity directly from the surface of the brain. This type of monitoring is typically done in specialized centers, and may require that you travel outside of the Greenville area.
The neurobehavioral examination is listed here because it is usually performed during a separate visit, much like the other office-based procedures. The neurobehavioral examination is very useful for identifying the presence of specific types of cognitive abnormalities, such as language or memory impairment. It is essential for the diagnosis of a dementia syndrome. It can be extremely useful in assessing recovery after stroke, head injury, or ongoing treatment of a neurological condition such as multiple sclerosis. Dr. Absher is one of only a few hundred behavioral neurologists in the United States, and one of only two board-certified behavioral neurologists in the state of South Carolina. He completed two years of subspecialty training in this area and has extensive clinical and research experience in the cognitive neurosciences related to behavioral neurology and neuropsychiatry. A complete description of the Neurobehavioral Examination is available elsewhere on this website.
Cranial computed tomography is basically an x-ray scan of the brain that is done in such a way that “slices” or tomographs are obtained. Regular x-rays are taken when the x-ray beams pass through the subject parallel to each other, and hit the flat piece of x-ray “film” positioned behind the subject. The concept of tomography was a revolutionary advance in brain imaging, because the x-rays and film are positioned in a circle around the subject. The computer creates a “slice” rather than a plane film picture. This can be done without injecting a contrast dye into your veins, or following the use of intravenous contrast. Contrast material makes blood vessels and other vascular structures show up much better than they do without contrast. The CT provides excellent information about brain structure, and whether there are any areas where contrast has leaked out of the blood vessels into brain tissue. Stroke, tumor, hemorrhage, infection, and a number of other important neurological conditions can be identified with a CT scan. Other parts of the nervous system besides the head (cranium) can certainly be imaged using CT technology. For the most part, Absher Neurology will utilize CT for the brain or spine. Spine CT is especially useful after contrast material has been injected into the spinal fluid for a myelogram procedure.
There is a small risk associated with the radiation exposure and with contrast injections that are sometimes necessary. Otherwise, the CT procedure carries little risk. Some people may require sedation for the procedure, because they are asked to lie very still on a table while the CT scan is obtained. Most of the time, the test only takes ten minutes or so, and no sedation is required.
MRI scanning is performed in much the same way as a CT scan. You are asked to lie on your back on the scanner, and images are created. The MRI scanner has a big opening inside a strong magnet. You will not notice the strong magnetic field, but you will hear loud noises. You will probably be asked to wear earplugs. Some people require sedation for this procedure because the scanning tube is somewhat narrow. If you are claustrophobic or afraid of small spaces, please be sure to let your doctor or the radiologist know prior to going into the tube.
No radiation exposure is required for MRI scanning, as there is with CT. There is negligible risk of kidney failure or allergic reactions to the contrast agents that are used for MRI. There is no risk to an MRI scan that we know of, in fact, other than the capability for a piece of metal to be heated or moved. This becomes important if you have had a recent stenting procedure for an occluded blood vessel, if you have had a prior experience where a metal fleck has lodged in your eye, if you have had a brain aneurysm clipped, or if you have a cardiac pacemaker. If there is any question in your mind about the possibility that you may not be an appropriate candidate for MRI, please be sure to bring this up with your doctor.
MRI is an excellent technique for imaging the nervous system. Incredible pictures of your spinal column, spinal cord, nerve roots, brain and brainstem can be obtained. There are many types of MRI scanning, including some types that can provide pictures of the blood vessels in your brain (MR angiography, or MRA). There is even a type of MRI scanning that can measure changes in blood flow within your brain so that it is possible to tell when specific brain areas are engaged in some sort of cognitive task (functional MRI or fMRI). Dr. Absher has experience with all of these techniques, and is certified by the American Society of Neuroimaging as a physician qualified to interpret both CT and MRI scans. In fact, Dr. Absher served for over 13 years on the committee charged with testing MRI knowledge among neurologists in training across the country. Absher Neurology takes pride in having the capability to provide professional interpretations for brain imaging studies, and to go over the results of your tests with you when you come in for evaluation. We believe that MRI and CT scans can be interpreted most appropriately when they are combined with other important information derived from a complete and thorough neurological assessment.
Ultrasound is a technique that uses high frequency sound waves to record important information, such as blood flow velocity and the size of blood vessels. When there is thickening in the wall of a blood vessel due to cholesterol build-up or bleeding into the wall of the blood vessel, ultrasound can tell us this. Also, if there is a blood clot in the middle of the vessel plugging it up, the ultrasound can show us a picture of this, and it can also indicate that blood flow velocity has changed dramatically. Either very high or low blood flow velocities may be significant.
The carotid arteries are the two large arteries supplying the brain through the front part of the neck. Carotid Doppler testing is a way to look at these arteries and determine if there may be a problem that puts the blood supply of your brain at risk. Even people who have not had a stroke might need to have their arteries repaired surgically if the problem is severe enough. Most of the time, only patients who have had evidence of small or major strokes would be candidates for surgical treatment. We perform the Carotid Doppler testing in our office a few times per month. Dr. Absher is certified by the American Society of Neuroimaging in the interpretation of both Carotid Doppler testing and Transcranial Doppler (TCD), as discussed below.
The carotid Doppler procedure is perfectly safe and is not painful. You simply lie on an examining table while the ultrasound technologist uses a probe to check the arteries on both sides of your neck. A little bit of clear gel is used to allow the sound waves to transfer between your skin and the probe more effectively. The entire procedure usually takes less than an hour, even when Doppler flow measurements and B mode imaging are both performed. The combined study, called carotid Duplex to indicate the two types of techniques used, can provide excellent pictures of the shape, thickness, and motion of arteries and veins in the neck, as well as an excellent estimate of the amount of narrowing within diseased blood vessels.
TCD is based on the same technology as carotid Doppler testing and other ultrasound techniques. The main difference between carotid and transcranial Doppler is that a different type of probe is used to measure blood flow velocity within the brain. The probe may be placed over your temples, your eyes, or over the back part of your head. Blood flow velocity within several different blood vessels in your brain can be estimated accurately. Pictures of the way your blood vessels look can also be created. The technique is extremely safe and may even have therapeutic benefit (although this is currently under investigation).
Dr. Absher is certified by the American Society of Neuroimaging in the use of this technique. In fact, Dr. Absher has been involved in clinical research involving advanced applications of this technology. The test is performed much the same way as a carotid Doppler study except for the fact that you may be permitted to sit up, or to change body positions during the study. One of the unique features of the TCD is that it can tell us what happens to blood flow when you turn your head or stand up. Sometimes such simple maneuvers can drastically alter brain blood flow, and the TCD is an excellent way to determine if this has occurred.
The echocardiogram is an advanced ultrasound technique. Although we have the capability of performing an echocardiogram in our office, a cardiologist or other qualified individual needs to perform the interpretation. The echocardiogram uses yet another type of probe to obtain information about the structure of your heart and the direction and speed of blood flow through the various chambers of your heart. Valve diseases, clots inside the heart, abnormal enlargement or weakness of heart muscle, and many other problems can be identified using this technique. If you have had a stroke, you will almost certainly need to have an echocardiogram. There are many other indications as well. We like to work closely in connection with your heart specialist so that we can understand the relevance of any findings on your echocardiogram to your overall neurological health.
The muscle biopsy is performed by a surgeon. A small piece of one of your larger leg muscles is obtained and placed in a special type of liquid to preserve it. The tissue is sent to a pathologist who performs special stains, and then examines the tissue under the microscope. The muscle biopsy can provide critical information regarding muscle diseases, and can help to distinguish a muscle disorder from a nerve problem. It usually takes a few weeks for the results of the muscle biopsy to return from the pathologist because it takes awhile to perform the special stains and the microscopic analysis. Prior to having a muscle biopsy, you will almost always need to have an EMG or nerve conduction study.
A surgeon performs the nerve biopsy. This is usually necessary in the setting of advanced peripheral nerve disorders, such as neuropathy, for which no clear cause has been established. Sometimes there is a suspicion of a treatable type of neuropathy, and the nerve biopsy is requested to confirm this impression. Most often, a small peripheral nerve in your foot or ankle is selected for biopsy, so that you will not notice much negative impact from the procedure. Most often, you will have a little bit of numbness on the side of your foot after the biopsy. Pain and swelling may persist for a couple weeks. It may take a few weeks for the results to become available from the pathologist, who performs special stains and microscopic analysis. Usually the nerve and muscle biopsy are performed by the same surgeon during the same procedure, since it is most often the case that nerve and muscles are affected together.
If you are suspected of having a neuromuscular junction disorder, such as myasthenia gravis or the Lambert-Eaton myasthenic syndrome, then you may have a Tensilon test. Tensilon is the brand name of a drug called edrophonium chloride. It causes rapid improvement in the motor weakness seen in many patients with myasthenia gravis. To have this test, you will need to be hooked up to a heart monitor temporarily. You will be warned about the potential risks of the procedure, which include a change in your heart rhythm. You may have a significant slowing of your heart, for example. Your doctor will need to start an intravenous line, and then you will receive an injection of either the drug or salt water (placebo). Neither you nor your doctor will know which medicine is the active drug, and which one is the salt water, until after the test is over. The goal of the test is to determine which injection contained the medicine that was supposed to make you stronger. Sometimes EMG will be recorded at the same time, or you will have repetitive nerve stimulation testing, both at baseline and following the injection. The test carries minimal risk when performed in a controlled setting, and may be a valuable diagnostic tool for patients with suspected neuromuscular junction deficits.
There are too many individual blood tests to describe all of them here. Blood testing is very useful for routine monitoring of side effects from medications, as well as for making specific diagnoses. Certain rare and unusual disorders can be screened using blood testing. Genetic analysis is available, for example, to diagnose inherited neurological conditions such as HuntingtonÕs disease. If you have specific questions about the blood work that your doctor is ordering, be sure to ask. In the future, we will expand this part of the website to include a brief description of some of the most typical blood tests that are done at Absher Neurology. You should check back here from time to time if you have frequent blood testing or questions that were not addressed during your visit.
Routine urinalysis can uncover problems, such as blood or protein in your urine, infection, or even dehydration. Twenty-four hour urine collections may also be useful for metabolic or endocrine conditions and certain rare genetic disorders. You may be asked to collect your specimen in a special bottle to protect it from sunlight, or to keep it refrigerated. Usually we will be able to provide you with specimen bottles, but in some situations, you may need to go to the laboratory to pick them up. Blood and urine specimens may be collected in the office, and then picked up by laboratory personnel for processing. This makes things convenient for you, and helps us assure that all of the appropriate tests are ordered properly.
The use of contrast dye to take a picture of the blood vessels in your brain is called cerebral angiography. Usually the large vessels in the thorax and neck are also examined. This procedure can only be done in a hospital equipped with a special room and appropriate equipment. The radiologist may give you a mild sedative. You will lie on the examining table. Your groin area or your arm will be cleansed with a special solution, and sterile drapes will be placed over the area. The radiologist will wear protective equipment just like you were having an operation. A tiny puncture will be made in the skin using the tip of a scalpel, to make it easier for the catheter to slide into your artery. A long catheter will be guided up into the major arteries in your chest that supply blood to your brain. A rapid series of x-rays will be obtained after contrast dye is injected, to get a clear picture of the arteries as well as the veins draining your brain. This test provides the best picture of certain types of blood vessel disorders, such as brain aneurysm, arteriovenous malformation (AVM), cerebral vasculitis, arterial dissection (hemorrhage into the wall of a blood vessel causing it to close up), and occlusive disease. After the procedure is over, you will be asked to remain in bed for up to six hours. There is also a type of technique to close the artery so that you may be able to get up and move around more quickly than this. The procedure is often performed as an outpatient. If you are already in the hospital for a stroke or some other condition, the procedure may be done while you are hospitalized. There is a small risk of stroke, dye reaction, and even death associated with the cerebral angiogram. The test is therefore reserved for situations in which there is a clear need for the information it provides.
Electrical recording of brain activity can be made in conjunction with visual, auditory, or somatosensory (skin) stimulation. For example, lights can be flashed in your eyes while you stare at a computer screen, or repeated “clicks” can be played through headphones. Similarly, one foot or one hand may be repeatedly stimulated by a small electric shock. The electrical response generated by your brain can be detected immediately following such auditory, visual, or somatosensory stimuli. By averaging the brain electrical activity over several hundred trials, a picture of the average pattern of your brain’s electrical responses can be obtained. This is called evoked potential testing. It may be useful for identifying the location of disorders of the brainstem, spinal cord, and other parts of the nervous system. It can be used to detect a problem in the pathways to the brain (as when somatosensory evoked potentials are recorded during neurosurgical procedures of the spinal cord). We can perform this test in our office. We may also choose to have the test performed while you are admitted to the hospital. The test is perfectly safe, and is performed in much the same way as an EEG.
There is often a need for a sophisticated evaluation of balance in the setting of dizziness or wobbliness. There are facilities in town that provide access to a device that performs a type of testing called dynamic posturography. When you are sent for such a procedure, you will be assessed by a physical therapist and evaluated with the device. Your ability to maintain your body position under various sorts of challenges will be examined in detail. For example, you may be blindfolded, or the platform you are standing on may be moved. Both types of challenges may be presented at the same time. This type of testing is an excellent way to determine the type of balance difficulty that you are experiencing, and may be very useful in terms of your ongoing evaluation and management for gait or balance difficulties.
For the most part, when you have bladder difficulties that are concerning to your neurologist, you may be referred to see a urologist. Occasionally we will order urodynamic testing at the same time. This is a type of bladder testing that can help to differentiate bladder muscle weakness and nervous system disturbances that contribute to bladder dysfunction. A catheter is placed inside your bladder and pressure measurements are obtained as your bladder is gradually filled up with water. The test has to be interpreted by a urologist. There are no risks to the procedure, but it can be a little bit uncomfortable.
The ENG is a test usually performed by an ENT physician or Otolaryngologist. As with urodynamic testing, you will usually be referred for an ENT consultation rather than simply an ENG procedure. The test is interpreted by an ENT physician or neurologist. The ENG helps us to understand whether there are difficulties in the connections between the balance organs in your ear (vestibular apparatus) and your brain. It also helps us understand whether the vestibular apparatus is functioning properly. The ENG is most useful in distinguishing between so-called “central” or brain-related types of dizziness, and those that are “peripheral” (i.e., related to damage to the inner ear or the nerves connecting the inner ear to the brain). The test is very safe. It simply involves placing some electrodes around your eyes to record eye movements, and squirting water into your ears in order to produce the eye movements. You may become nauseated and you might even vomit during the procedure. The nausea is only temporary and usually subsides within a few minutes after the procedure is over. The test provides important information about dizziness and imbalance.
The Transesophageal Echocardiogram (TEE) is a type of echocardiogram (described elsewhere) that provides a better picture of heart valves and the chambers of the heart than the typical “transthoracic” echocardiogram. A tube is inserted down the throat with an ultrasound probe attached to the end of the tube. Patients who are overweight (making transthoracic echocardiography less accurate) or in whom there is a very high risk of stroke due to heart problems are good candidates for TEE. The test usually requires some sedation so that the gag reflex is minimized while the tube is inside the throat. There are some minor risks associated with the procedure, but it is very safe and provides excellent information about heart structure and function. A cardiologist performs this procedure, usually in the setting of acute stroke evaluation.
Monitoring electrical activity from the heart is important for detecting irregularities that can lead to passing out, stroke, dizzy spells, and other neurological symptoms. The test is performed by applying electrodes over the chest, attached to a small device that is carried around for days to weeks. In some cases, the device records continuously. In others, the device may be activated whenever strange symptoms occur. In this manner, heart irregularities can be identified that may play a role in neurological symptoms. Most often a technician applies the equipment but a cardiologist does the interpretation. There are no risks to the procedure.
Part of the evaluation for passing out spells, or syncope, may include a tilt table test. This test is performed in a special laboratory equipped with a table that can be tilted to any angle. When the patient first begins the test, he or she is lying flat on the table. The table’s elevation is gradually increased, and heart rate and blood pressure are monitored carefully. Often, patients will exhibit signs of passing out or dizziness. There may be associated heart rhythm changes or blood pressure changes during the test. The tilt table test can provide extremely useful information regarding the cause of passing out spells. Often the test helps to determine the most appropriate drug treatments for episodes of loss of consciousness. There are very few risks to the procedure other than the possibility that loss of consciousness may occur, along with some dizziness, nausea, or vomiting.
Prolonged blood pressure monitoring can be very useful to establish fluctuations in blood pressure that may relate to episodes of dizziness or loss of consciousness. Unfortunately, Medicare and many insurance companies fail to accept the value of this procedure, and will not authorize payment. The test is the best way to determine the overall severity of high blood pressure (hypertension), and the magnitude of blood pressure fluctuations from one time to another during the course of a day. Dr. Absher has extensive experience with this technique, and has found surprising results in his research. For example, blood pressure levels that are not normally thought to be dangerous may be associated with episodes of loss of consciousness and impaired brain blood flow in patients with chronic high blood pressure. These and other findings suggest that ambulatory blood pressure monitoring may well prove to be an extremely valuable tool for assessing stroke risk. There are no risks to this procedure.
In patients suspected of having a metabolic disorder affecting their muscles, the ischemic forearm muscle test may be completed in the office. During this test, a blood pressure cuff is inflated on the arm, and repeated blood samples are obtained. The blood samples are sent to the lab to check for the build-up of lactic acid and creatine kinase. In patients with certain types of metabolic muscle diseases, these levels will fall outside of the normal range, and they will fail to clear appropriately when the blood pressure cuff is removed. There are no risks to the procedure, which is only rarely necessary in clinical practice.
A neuropsychologist is a psychologist who is specially trained in the administration and interpretation of mental tests, such as memory and language tests. Neuropsychological testing is a far more formalized and standardized type of cognitive testing than the neurobehavioral examination, which is administered by a physician. The neurobehavioral exam and neuropsychological assessment share some features in common, however, such as the ability to detect impairments in specific aspects of cognitive function (e.g., language, memory, attention). On the other hand, if precise measurements are required over time, if litigation might be involved, or if the person being tested has an extremely high or low baseline intellectual capability, then neuropsychological testing is probably the preferred method to assess cognitive ability. Testing may take several hours, and may be somewhat frustrating for the participant. Other than this, there are no risks to the procedure.
The Positron Emission Tomography (PET) scan is a type of brain imaging test that can measure a variety of things. Brain glucose metabolism can be measured if a form of glucose (sugar) labeled with radioactivity, called 18FDG, is used as the tracer material. Other types of tracers may also be used. It is possible to measure the rate of blood flow to different parts of the brain, the amount of oxygen metabolized in different parts of the brain, and the volume of blood present in specific parts of the brain. Radioactive drugs can be made in the laboratory and injected so that the amount and pattern of drug binding in specific parts of the brain can be measured and mapped. These tracers, called ligands, may be used to determine whether normal drug binding levels are present in specific parts of the brain that may be affected by disease. For example, dopamine binding may decrease in patients with ParkinsonÕs disease. Using the techniques of image averaging and subtraction, or more sophisticated statistical techniques, changes in all of these variables can be mapped on a region-by-region basis. Such activation studies continue to fascinate brain scientists and generate new insights into brain organization and function. Unfortunately, many insurance companies, including Medicare, frequently deny payment for the cost of PET scanning, except in selected oncology patients, refractory seizure patients, and a few other uncommon situations. There are some risks associated with PET scanning, including radiation exposure and the need for arterial or intravenous catheters.
The Single Photon Emission Computed Tomography (SPECT) scan is similar to a PET scan. A picture of brain blood flow can be obtained. Ligand studies are also possible. SPECT scanners are more widely available than PET scanners, and it is usually a little bit easier to get Medicare or other insurance companies to pay for the SPECT scan. Unfortunately, the images are usually not as accurate as those obtained from a PET scanner, and it is more difficult to perform “activation studies” than it is with the PET scanner. The test does require a small radiation exposure, as does the PET scan. Other than this, there are no substantial risks to the procedure, but an intravenous catheter may be required.
The WADA test requires a cerebral angiogram. An anesthetic, such as sodium amobarbital, is injected into an artery within one side of the brain. This effectively puts part of the brain to sleep. It is possible to perform clinical tests on an awake patient to see which part of the brain has fallen asleep. The test is important in presurgical planning. For example, if putting to sleep someoneÕs right temporal lobe severely disturbs memory functioning, the surgeon will be much more reluctant to remove that temporal lobe as a treatment for epilepsy. The test carries all of the risks of the angiogram. In addition, there is some risk associated with false information. Sometimes the WADA test suggests that it is safe to remove a part of the brain, but the post-surgical assessment reveals unanticipated problems. While there are risks to the procedure, the information generally improves the state of knowledge that would exist without such a procedure.
Functional magnetic resonance imaging, or fMRI, is a research tool at this time. However, clinical applications are rapidly evolving. Dr. Absher has significant experience with this modality. fMRI can be used to determine which parts of the brain participate in specific types of cognitive or mental tasks, just like a WADA test. It can also be used for cognitive neuroscience research. Very small changes in brain blood flow within minute areas of the brain can be estimated. Quantitative measurements are not possible, but a percentage change in blood flow can be readily determined. The test is rapidly gaining popularity as one of the more important methods for mapping human brain function so that we may understand better how it accomplishes the amazing things that it does. We have devoted a section of our website specifically to this fascinating technique. It is one of the major goals of Absher Neurology to continue research in fMRI and to bring this important tool into the clinical arena right here in Greenville. Please, stay tuned for further developments.