The neurological exam is a clinical assessment tool used to determine what specific parts of the CNS are affected by damage or disease. It can be performed in a short time—sometimes as quickly as 5 minutes—to establish neurological function. In the emergency department, this rapid assessment can make the difference with respect to proper treatment and the extent of recovery that is possible.

The exam is a series of subtests separated into five major sections. The first of these is the mental status exam, which assesses the higher cognitive functions such as memory, orientation, and language. Then there is the cranial nerve exam, which tests the function of the 12 cranial nerves and, therefore, the central and peripheral structures associated with them. The cranial nerve exam tests the sensory and motor functions of each of the nerves, as applicable. Two major sections, the sensory exam and the motor exam, test the sensory and motor functions associated with spinal nerves. Finally, the coordination exam tests the ability to perform complex and coordinated movements. The gait exam, which is often considered a sixth major exam, specifically assesses the motor function of walking and can be considered part of the coordination exam because walking is a coordinated movement.

Localization of function is the concept that circumscribed locations are responsible for specific functions. The neurological exam highlights this relationship. For example, the cognitive functions that are assessed in the mental status exam are based on functions in the cerebrum, mostly in the cerebral cortex. Several of the subtests examine language function. Deficits in neurological function uncovered by these examinations usually point to damage to the left cerebral cortex. In the majority of individuals, language function is localized to the left hemisphere between the superior temporal lobe and the posterior frontal lobe, including the intervening connections through the inferior parietal lobe.

The five major sections of the neurological exam are related to the major regions of the CNS (Figure). The mental status exam assesses functions related to the cerebrum. The cranial nerve exam is for the nerves that connect to the diencephalon and brain stem (as well as the olfactory connections to the forebrain). The coordination exam and the related gait exam primarily assess the functions of the cerebellum. The motor and sensory exams are associated with the spinal cord and its connections through the spinal nerves.

Part of the power of the neurological exam is this link between structure and function. Testing the various functions represented in the exam allows an accurate estimation of where the nervous system may be damaged. Consider the patient described in the chapter introduction. In the emergency department, he is given a quick exam to find where the deficit may be localized. Knowledge of where the damage occurred will lead to the most effective therapy.

In rapid succession, he is asked to smile, raise his eyebrows, stick out his tongue, and shrug his shoulders. The doctor tests muscular strength by providing resistance against his arms and legs while he tries to lift them. With his eyes closed, he has to indicate when he feels the tip of a pen touch his legs, arms, fingers, and face. He follows the tip of a pen as the doctor moves it through the visual field and finally toward his face. A formal mental status exam is not needed at this point; the patient will demonstrate any possible deficits in that area during normal interactions with the interviewer. If cognitive or language deficits are apparent, the interviewer can pursue mental status in more depth. All of this takes place in less than 5 minutes. The patient reports that he feels pins and needles in his left arm and leg, and has trouble feeling the tip of the pen when he is touched on those limbs. This suggests a problem with the sensory systems between the spinal cord and the brain. The emergency department has a lead to follow before a CT scan is performed. He is put on aspirin therapy to limit the possibility of blood clots forming, in case the cause is an embolus—an obstruction such as a blood clot that blocks the flow of blood in an artery or vein.

Damage to the nervous system can be limited to individual structures or can be distributed across broad areas of the brain and spinal cord. Localized, limited injury to the nervous system is most often the result of circulatory problems. Neurons are very sensitive to oxygen deprivation and will start to deteriorate within 1 or 2 minutes, and permanent damage (cell death) could result within a few hours. The loss of blood flow to part of the brain is known as a stroke, or a cerebrovascular accident (CVA).

There are two main types of stroke, depending on how the blood supply is compromised: ischemic and hemorrhagic. An ischemic stroke is the loss of blood flow to an area because vessels are blocked or narrowed. This is often caused by an embolus, which may be a blood clot or fat deposit. Ischemia may also be the result of thickening of the blood vessel wall, or a drop in blood volume in the brain known as hypovolemia.

A related type of CVA is known as a transient ischemic attack (TIA), which is similar to a stroke although it does not last as long. The diagnostic definition of a stroke includes effects that last at least 24 hours. Any stroke symptoms that are resolved within a 24-hour period because of restoration of adequate blood flow are classified as a TIA.

A hemorrhagic stroke is bleeding into the brain because of a damaged blood vessel. Accumulated blood fills a region of the cranial vault and presses against the tissue in the brain (Figure). Physical pressure on the brain can cause the loss of function, as well as the squeezing of local arteries resulting in compromised blood flow beyond the site of the hemorrhage. As blood pools in the nervous tissue and the vasculature is damaged, the blood-brain barrier can break down and allow additional fluid to accumulate in the region, which is known as edema.

Whereas hemorrhagic stroke may involve bleeding into a large region of the CNS, such as into the deep white matter of a cerebral hemisphere, other events can cause widespread damage and loss of neurological functions. Infectious diseases can lead to loss of function throughout the CNS as components of nervous tissue, specifically astrocytes and microglia, react to the disease. Blunt force trauma, such as from a motor vehicle accident, can physically damage the CNS.

A class of disorders that affect the nervous system are the neurodegenerative diseases: Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis (ALS), Creutzfeld–Jacob disease, multiple sclerosis (MS), and other disorders that are the result of nervous tissue degeneration. In diseases like Alzheimer’s, Parkinson’s, or ALS, neurons die; in diseases like MS, myelin is affected. Some of these disorders affect motor function, and others present with dementia. How patients with these disorders perform in the neurological exam varies, but is often broad in its effects, such as memory deficits that compromise many aspects of the mental status exam, or movement deficits that compromise aspects of the cranial nerve exam, the motor exam, or the coordination exam. The causes of these disorders are also varied. Some are the result of genetics, such as Huntington’s disease, or the result of autoimmunity, such as MS; others are not entirely understood, such as Alzheimer’s and Parkinson’s diseases. Current research suggests that many of these diseases are related in how the degeneration takes place and may be treated by common therapies.

Finally, a common cause of neurological changes is observed in developmental disorders. Whether the result of genetic factors or the environment during development, there are certain situations that result in neurological functions being different from the expected norms. Developmental disorders are difficult to define because they are caused by defects that existed in the past and disrupted the normal development of the CNS. These defects probably involve multiple environmental and genetic factors—most of the time, we don’t know what the cause is other than that it is more complex than just one factor. Furthermore, each defect on its own may not be a problem, but when several are added together, they can disrupt growth processes that are not well understand in the first place. For instance, it is possible for a stroke to damage a specific region of the brain and lead to the loss of the ability to recognize faces (prosopagnosia). The link between cell death in the fusiform gyrus and the symptom is relatively easy to understand. In contrast, similar deficits can be seen in children with the developmental disorder, autism spectrum disorder (ASD). However, these children do not lack a fusiform gyrus, nor is there any damage or defect visible to this brain region. We conclude, rather poorly, that this brain region is not connected properly to other brain regions.

Infection, trauma, and congenital disorders can all lead to significant signs, as identified through the neurological exam. It is important to differentiate between an acute event, such as stroke, and a chronic or global condition such as blunt force trauma. Responses seen in the neurological exam can help. A loss of language function observed in all its aspects is more likely a global event as opposed to a discrete loss of one function, such as not being able to say certain types of words. A concern, however, is that a specific function—such as controlling the muscles of speech—may mask other language functions. The various subtests within the mental status exam can address these finer points and help clarify the underlying cause of the neurological loss.

Review

The neurological exam is a clinical assessment tool to determine the extent of function from the nervous system. It is divided into five major sections that each deal with a specific region of the CNS. The mental status exam is concerned with the cerebrum and assesses higher functions such as memory, language, and emotion. The cranial nerve exam tests the functions of all of the cranial nerves and, therefore, their connections to the CNS through the forebrain and brain stem. The sensory and motor exams assess those functions as they relate to the spinal cord, as well as the combination of the functions in spinal reflexes. The coordination exam targets cerebellar function in coordinated movements, including those functions associated with gait.

Damage to and disease of the nervous system lead to loss of function. The location of the injury will correspond to the functional loss, as suggested by the principle of localization of function. The neurological exam provides the opportunity for a clinician to determine where damage has occurred on the basis of the function that is lost. Damage from acute injuries such as strokes may result in specific functions being lost, whereas broader effects in infection or developmental disorders may result in general losses across an entire section of the neurological exam.

A neurological examination assesses motor and sensory skills, hearing and speech, vision, coordination, and balance. It may also test mental status, mood, and behavior. The examination uses tools such as a tuning fork, flashlight, reflex hammer, and a tool for examining the eye. The results of the neurological examination and the patient’s history are used to determine a list of possibilities, known as the differential diagnosis, that help determine which additional diagnostic tests and procedures are needed.

Diagnostic tests and procedures are vital tools that help physicians confirm or rule out the presence of a neurological disorder or other medical condition. A century ago, the only way to make a positive diagnosis for many neurological disorders was by performing an autopsy after a patient had died. But decades of basic research into the characteristics of disease, and the development of techniques that allow scientists to see inside the living brain and monitor nervous system activity as it occurs, have given doctors powerful and accurate tools to diagnose disease and to test how well a particular therapy may be working.

Perhaps the most significant changes in diagnostic imaging over the past 20 years are improvements in spatial resolution (size, intensity, and clarity) of anatomical images and reductions in the time needed to send signals to and receive data from the area being imaged. These advances allow physicians to simultaneously see the structure of the brain and the changes in brain activity as they occur. Scientists continue to improve methods that will provide sharper anatomical images and more detailed functional information.

Researchers and physicians use a variety of diagnostic imaging techniques and chemical and metabolic analyses to detect, manage, and treat neurological disease. Some procedures are performed in specialized settings, conducted to determine the presence of a particular disorder or abnormality. Many tests that were previously conducted in a hospital are now performed in a physician’s office or at an outpatient testing facility, with little if any risk to the patient. Depending on the type of procedure, results are either immediate or may take several hours to process.

Laboratory screening tests of blood, urine, or other body fluids may help doctors diagnose disease, understand disease severity, and monitor levels of therapeutic drugs. Certain tests, ordered by the physician as part of a regular check-up, provide general information, while others are used to identify specific health concerns. For example, blood tests can provide evidence for infections, toxins, clotting disorders, or antibodies that signal the presence of an autoimmune disease. Genetic testing of DNA extracted from cells in the blood or saliva can be used to diagnose hereditary disorders. Analysis of the fluid that surrounds the brain and spinal cord can detect meningitis, encephalitis, acute and chronic inflammation, viral infections, multiple sclerosis, and certain neurodegenerative disorders. Chemical and metabolic testing of the blood can indicate some muscle disorders, protein or fat-related disorders that affect the brain and inborn errors of metabolism. Blood tests can monitor levels of therapeutic drugs used to treat epilepsy and other neurological disorders. Analyzing urine samples can reveal toxins, abnormal metabolic substances, proteins that cause disease, or signs of certain infections.

Genetic testing of people with a family history of a neurological disease can determine if they are carrying one of the genes known to cause the disorder. Genetic counseling may be recommended for patients, or parents of children being tested, to help them understand the purpose of the tests and what the results could mean. Genetic testing that is used for diagnosis or treatment should be done in a laboratory that has been certified for clinical testing. Clinical testing can look for mutations in specific genes or in certain regions of several genes. This testing may use a panel of genes for a specific type of disease (for example, infant-onset epilepsy) or a test known as whole exome sequencing. Exomes are the parts of the genome formed by exons, which code for proteins. Exome sequencing may take several months to analyze. Clinicians and researchers also sequence whole exomes or whole genomes to discover new genes that cause neurological disorders. These genes may eventually be used for clinical testing in more focused panels.

Prenatal genetic testing can identify many neurological disorders and genetic abnormalities in utero (while the child is inside the mother’s womb).

• The mother’s blood can be screened for abnormalities that suggest a risk for a genetic disorder. Cell-free DNA from the mother’s blood can also be used to look for Down syndrome and some chromosomal disorders.
• Doctors may also use a type of blood test called a triple screen in order to identify some genetic disorders, including trisomies (disorders such as Down syndrome in which the fetus has an extra chromosome) in an unborn baby. A blood sample is taken from a pregnant woman and tested for three substances: alpha-fetoprotein, human chorionic gonadotropin, and estriol. The test is performed between the 15th and 20th week of pregnancy. It usually takes several days to receive results from a triple screen. Abnormal results of a triple screen may indicate a possible problem such as spina bifida (the incomplete development of the brain, spinal cord, or the cord’s protective coverings) or a chromosome abnormality. However, the test has many false positive results, so additional testing is needed to confirm if there is a problem.
• Amniocentesis is usually done at 14-16 weeks of pregnancy. It tests a sample of the amniotic fluid in the womb for genetic defects (the cells found in the fluid and the fetus have the same DNA). Under local anesthesia, a thin needle is inserted through the woman’s abdomen and into the womb. About 20 milliliters of fluid (roughly 4 teaspoons) is withdrawn and sent to a lab for evaluation. Test results often take 1-2 weeks.
• Chorionic villus sampling is performed by removing and testing a very small sample of the placenta during early pregnancy. The sample, which contains the same DNA as the fetus, is removed by catheter or fine needle inserted through the cervix or by a fine needle inserted through the abdomen. Results are usually available within 2 weeks.

Brain scans include several types of imaging techniques used to diagnose tumors, blood vessel malformations, stroke, injuries, abnormal brain development, and hemorrhage in the brain. Types of brain scans include computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and single proton emission (SPECT) scans.

• Computed tomography (CT scan) uses X-rays to produce two-dimensional images of organs, bones, and tissues. A CT scan can aid in proper diagnosis by showing the area of the brain that is affected. CT scans can be used to quickly detect hemorrhage in the brain and to determine if someone who has had a stroke can safely receive intravenous treatment to dissolve clots. CT scans also may be used to detect bone and vascular irregularities, brain tumors and cysts, brain damage from head injury, hydrocephalus, brain damage causing epilepsy, and encephalitis, among other disorders. A contrast dye may be injected into the bloodstream to highlight the different tissues in the brain. A CT of the spine can be used to show herniated discs, spine fractures, or spinal stenosis (narrowing of the spinal canal).
  
  CT scanning takes about 20 minutes and is usually done at an outpatient imaging center or in a hospital. The person lies on a special table that slides into a narrow, doughnut-shaped chamber. A sound system built into the chamber allows the person to communicate with the physician or technician. X-rays (ionizing radiation) are passed through the body at various angles and are detected by a computerized scanner. The data is processed and displayed as cross-sectional images, or “slices,” of the internal structure of the body or organ. Occasionally a light sedative may be given if the person is unable to lie still and pillows may be used to support and stabilize the head and body.
  
  If a contrast dye is injected into a vein, the individual being scanned may feel a warm or cool sensation as the dye circulates through the bloodstream or may experience a slight metallic taste. CT scans are particularly useful in people who are unable to undergo MRI. Because CT uses X-rays, pregnant women should avoid the test because of potential harm to the fetus.

Magnetic resonance imaging (MRI) uses computer-generated radio waves and a powerful magnetic field to produce detailed images of body tissues. Using different sequences of magnetic pulses, MRI can show anatomical images of the brain or spinal cord, measure blood flow, or reveal deposits of minerals such as iron. MRI is used to diagnose stroke, traumatic brain injury, brain and spinal cord tumors, inflammation, infection, vascular irregularities, brain damage associated with epilepsy, abnormally developed brain regions, and some neurodegenerative disorders. MRI is also used to diagnose and monitor disorders such as multiple sclerosis. A contrast dye may be injected into the vein to enhance visibility of certain areas or tissues.

An MRI scanner consists of a tube surrounded by a very large cylindrical magnet. These scanners create a magnetic field around the body that’s strong enough to temporarily realign water molecules in the tissues. Radio waves are then passed through the body to detect the shifting of molecules back to a random alignment. A computer then reconstructs a three-dimensional picture or a two-dimensional “slice” of the tissue being scanned. MRI can distinguish between bone, soft tissues, and fluid-filled spaces because of differences in water content and tissue properties. The individual lies on a special table that slides into the tube and will be asked to remove jewelry, eyeglasses, removable dental work, clothing with metal and other items that might interfere with the magnetic imaging. The person may hear grating or knocking noises when the magnetic field direction is flipped. Earphones or earplugs can help block out the sounds. For brain MRI scans, a detector is placed over the head.

Due to the incredibly strong magnetic field generated by an MRI, people with implanted medical devices such as a pacemaker or infusion device generally should not have MRIs. In certain circumstances facilities may have equipment to temporarily stop and reset the implanted device’s programming in order to allow MRI.

Unlike CT scanning, MRI does not use ionizing radiation to produce images. The test is painless and risk-free, although persons who are obese or claustrophobic may find it somewhat uncomfortable. Depending on the part(s) of the body to be scanned, MRI can take up to an hour to complete. Some centers use open MRI machines that do not completely surround the person being tested and are less confining. However, open MRI does not currently provide the same picture quality as standard MRI and some tests may not be available using this equipment.

Because people must remain still during the MRI, children may need to be sedated in order to be scanned. If intravenous contrast is required, people may first need a blood test to check kidney function because the contrast agent, called gadolinium, can increase the risk of a rare disease in people with advanced kidney disease.

A fetal MRI may be ordered when prenatal ultrasound reveals a possible problem with a fetus, Fetal MRI is considered safe for the baby because it does not require radiation or contrast dye.

Functional MRI (fMRI) uses the blood’s magnetic properties to produce real-time images of blood flow to particular areas of the brain. fMRI can pinpoint areas of the brain that become active and show how long they stay active. This imaging process may be used to localize brain regions for language, motor function, or sensation prior to surgery for epilepsy. Researchers use fMRI to study head injury and degenerative disorders such as Alzheimer’s disease.

Positron emission tomography (PET) scans provide two- and three-dimensional pictures of brain activity by measuring radioactive isotopes that are injected into the bloodstream. PET scans of the brain are used to detect or highlight tumors and diseased tissue, show blood flow, and measure cellular and/or tissue metabolism. PET scans can be used to evaluate people who have epilepsy or certain memory disorders, and to show brain changes following injury. PET may be ordered as a follow-up to a CT or MRI scan to give the physician a greater understanding of specific areas of the brain that may be involved with problems. PET scans are performed by skilled technicians at highly sophisticated medical facilities in a hospital or at an outpatient testing facility. A low-level radioactive isotope, also called a tracer, is injected into the bloodstream and the tracer’s uptake in the brain is measured. The perosn lies still while overhead sensors detect gamma rays in the body’s tissues. A computer processes the information and displays it on a video monitor or on film. Using different compounds, more than one brain function can be traced simultaneously. PET is painless and uses small amounts of radioactivity. The length of test time depends on the part of the body to be scanned.

Single photon emission computed tomography (SPECT) is a nuclear imaging test that can be used to evaluate certain brain functions. As with a PET scan, a radioactive isotope, or tracer, is injected intravenously into the body. A SPECT scan may be ordered as a follow-up to an MRI to diagnose tumors, infections, brain regions involved in seizures, degenerative spine disease, and stress fractures. A dopamine transporter imaging with single-photon emission computed tomography (DaT-SPECT) scan can be used to help diagnose Parkinson disease. During a SPECT scan, the person lies on a table while a gamma camera rotates around the head and records where the radioisotope has traveled. hat information is converted by computer into cross-sectional slices that are stacked to produce a detailed three-dimensional image of tracer within the brain. The test is performed at either an outpatient imaging center or a hospital.

Angiography is a test that involves injecting dye into the arteries or veins to detect blockage or narrowing. A cerebral angiogram can show narrowing or obstruction of an artery or blood vessel in the brain, head, or neck. It can determine the location and size of an aneurysm or vascular malformation. Angiograms are used in certain strokes where there is a possibility of unblocking the artery using a clot retriever. Angiograms can also show the blood supply of a tumor prior to surgery or embolectomy (surgical removal of a blood clot or other material that is blocking a blood vessel).

Angiograms are usually performed in a hospital outpatient or inpatient setting and may take up to 3 hours, followed by a 6- to 8-hour resting period. The person, wearing a hospital or imaging gown, lies on a table that is wheeled into the imaging area. A physician anesthetizes a small area of the leg near the groin and then inserts a catheter into a major artery located there. The catheter is threaded through the body and into an artery in the neck. Dye is injected and travels through the bloodstream into the head and neck. A series of x-rays is taken. The person may feel a warm to hot sensation or slight discomfort as the dye is released. In many situations, cerebral angiograms have been replaced by specialized MRI scans, called MR angiograms (MRA), or CT angiograms. A spinal angiogram is used to detect blockage of arteries or blood vessels malformations in the vessels to the spinal cord.

Biopsy involves the removal and examination of a small piece of tissue from the body. Muscle or nerve biopsies are used to diagnose neuromuscular disorders. A small sample of muscle or nerve is removed under local anesthetic (pain-relieving medication) and studied under a microscope. The muscle sample may be removed either surgically, through a slit made in the skin, or by needle biopsy, in which a thin hollow needle is inserted through the skin and into the muscle. A piece of the nerve may be removed through a small surgical incision near the ankle, or occasionally near the wrist. Muscle and nerve biopsies are usually performed in an outpatient testing facility. A skin biopsy can be used to measure small nerve fibers or to test for certain metabolic disorders. A small piece of skin is removed under local anesthesia, usually in an office setting. A brain biopsy, used to determine tumor type or certain infections, requires surgery to remove a small piece of the brain or tumor. A brain biopsy is an invasive procedure that carries its own risks.

Cerebrospinal fluid analysis involves the removal of a small amount of the fluid that surrounds the brain and spinal cord. The procedure is commonly called a lumbar puncture or spinal tap. The fluid is tested to detect evidence of brain hemorrhage, infection, multiple sclerosis, metabolic diseases, or other neurological conditions. Pressure inside the skull can be measured to detect conditions such as a false brain tumor. The lumbar puncture may be done as an inpatient or as an outpatient procedure. During the lumbar puncture the person will either lie on one side, with knees close to the chest, or lean forward while sitting on a table, bed, or massage chair. The perosn’s back will be cleaned and injected with a local anesthetic. The injection may cause a slight stinging sensation. Once the anesthetic has taken effect, a special needle is inserted between the vertebrae into the spinal sac and a small amount of fluid (usually about three teaspoons) is withdrawn for testing. Most people will only feel a sensation of pressure as the needle is inserted. Generally, people are asked to lie flat for an hour or two to reduce the after-effect of headache. There is a small risk of nerve root injury or infection from a lumbar puncture. The procedure takes about 45 minutes.

Electroencephalography, or EEG, monitors the brain’s electrical activity through the skull. EEG is used to help diagnose seizure disorders and metabolic, infectious, or inflammatory disorders that affect the brain’s activity. EEGs are also used to evaluate sleep disorders, monitor brain activity when a person has been fully anesthetized or loses consciousness, and may be used to confirm brain death.

This painless, risk-free test can be performed in a doctor’s office or at a hospital or testing facility. A person being tested usually reclines in a chair or on a bed during the test. A series of cup-like electrodes are attached to the scalp with a special conducting paste. The electrodes are attached to wires (also called leads) that carry the electrical signals of the brain to a machine. During an EEG recording session, a variety of external stimuli, including bright or flashing lights, noise or certain drugs may be given.

Individuals may be asked to open and close their eyes, or to change their breathing patterns. Changes in brain wave patterns are transmitted to an EEG machine or computer. An EEG test usually takes about an hour. Testing for certain disorders requires performing an EEG during sleep, which takes at least 3 hours.

In people undergoing evaluation for epilepsy surgery, electrodes may be inserted through a surgical opening in the skull to reduce signal interference. This is called an intracranial EEG. People typically remain in a hospital epilepsy monitoring unit while implanted electrodes are in place. During this time, the brain is monitored for seizures in order to determine where the seizures originate. People may also be asked to perform certain types of tasks (e.g., reading, speaking, or certain limited motor activities) so that the EEG can be used to identify brain regions that are important for normal function.

Electromyography, or EMG, is used to diagnose nerve and muscle disorders, spinal nerve root compression, and motor neuron disorders such as amyotrophic lateral sclerosis. EMG records the electrical activity in the muscles. Muscles develop abnormal electrical signals when there is nerve or muscle damage. During an EMG, very fine needles or wires are inserted into a muscle to assess changes in electrical signals at rest and during movement. The needles are attached through wires to an EMG machine. Testing may take place in a doctor’s office or clinic and lasts an hour or longer, depending on the number of muscles and nerves to be tested. Because of a slight risk of bruising or bleeding, people will be asked if they are on aspirin or blood thinners. Most people find this test to be somewhat uncomfortable.

An EMG is usually done in conjunction with a nerve conduction study (NCS). An NCS measures the nerve’s ability to send a signal, as well as the speed (nerve conduction velocity) and size of the nerve signal. A set of recording electrodes is taped to the skin over the muscles or skin. Wires connect the electrodes to an EMG machine. A small electrical pulse (similar to the sensation of static electricity) is given on the skin a short distance away to stimulate the nerve to the muscle or skin. The electrical signal is viewed on the EMG machine. The physician then reviews the response to verify any nerve damage or muscle disease. There is minimal discomfort and no risk associated with this test.