Diagnostic tests for Neurologic Disorders

Focus Topic: Diagnostic tests for Neurologic Disorders

A complete nervous system evaluation typically includes imaging studies, angiography, and electrophysiologic studies. Keep in mind that while these Diagnostic tests for Neurologic Disorders may be routine for you, they can be frightening for the patient. It’s important to fully explain each procedure and carefully prepare him because stress and anxiety can affect test results.

Diagnostic tests for Neurologic Disorders: Imaging studies

The most common imaging studies used to detect neurologic disorders include:

  • computed tomography (CT) scan
  • isotope brain scan
  • magnetic resonance imaging (MRI)
  • positron emission tomography (PET)
  • skull and spinal X-rays.

Diagnostic tests for Neurologic Disorders: Computed tomography scan

CT scanning combines radiology and computer analysis of tissue density (determined by contrast dye absorption) to study intracranial structures. Although CT doesn’t show blood vessels as well as an angiogram, it carries less risk of complications and causes less trauma than cerebral angiography.

A scan for all seasons

A CT scan of the spine helps the practitioner to assess spinal disorders, such as a herniated disk, spinal cord tumors, and spinal stenosis. A CT scan of the brain can help detect:

  • brain contusion
  • brain calcifications
  • cerebral atrophy
  • hydrocephalus
  • inflammation
  • space-occupying lesions (tumors, hematomas, abscesses)
  • vascular anomalies (arteriovenous malformations [AVMs], infarctions, blood clots, hemorrhage). (See CT scans and strokes.)

CT scans and strokes

Diagnostic tests for Neurologic Disorders

 

Nursing considerations

  • Confirm that the patient isn’t allergic to iodine or shellfish. (A patient with these allergies may have an adverse reaction to the contrast medium and requires premedication with corticosteroids.)
  • If the test calls for a contrast medium, explain that an I.V. catheter will be inserted for injection of the contrast medium.
  • Explain to the patient that he may feel flushed or notice a metallic taste in his mouth when the contrast medium is injected (if used).
  • Tell him that the CT scanner will circle around him for 10 to 30 minutes (depending on the procedure and type of equipment) and that he must lie still during the test.

Good to go

  • Encourage the patient to resume normal activities and a regular diet after the test.
  • Explain that the contrast medium may discolor his urine for 24 hours, and suggest that he drink more fluids to help flush this medium out of his system.

Diagnostic tests for Neurologic Disorders: Isotope brain scan

In this procedure, a scanning device monitors the brain’s uptake of a radioactive isotope, such as technetium-99m pertechnetate. Damaged brain tissue absorbs more of the isotope than healthy tissue (probably due to an abnormally permeable blood-brain barrier). Although the brain scan can locate cerebral lesions and determine their size, it doesn’t reveal the cause — for example, whether it’s caused by a tumor, cerebral edema, an infarction, a hematoma, or an abscess.

Nursing considerations

  • Withhold medications, as ordered.
  • Confirm that the patient isn’t allergic to iodine or shellfish. (A patient with these allergies may have an adverse reaction to the contrast medium.)
  • Explain that an I.V. catheter will be inserted for injection of the contrast medium.
  • Tell him that he’ll be asked to change position several times during the procedure while a technician takes pictures of his brain.
  • Unless contraindicated, encourage the patient to drink more fluids to help flush the contrast medium out of his system.

Diagnostic tests for Neurologic Disorders: Magnetic resonance imaging

MRI generates detailed pictures of body structures. The test may involve the use of a contrast medium such as gadolinium.

Feeling superior

Compared with conventional X-rays and CT scans, MRI provides superior contrast of soft tissues, sharply differentiating healthy, benign, and cancerous tissue and clearly revealing blood vessels. In addition, MRI permits imaging in multiple planes, including sagittal and coronal views in regions where bones normally hamper visualization. MRI is especially useful for studying the CNS because it can detect the structural and biochemical abnormalities associated with such conditions as transient ischemic attacks (TIAs), tumors, multiple sclerosis (MS), cerebral edema, and hydrocephalus.

 

Nursing considerations

  • Explain to the patient that the procedure can take up to 11/2 hours and that he’ll have to remain still for intervals of 5 to 20 minutes.
  • Have the patient remove all metallic items, such as hair clips, bobby pins, jewelry (including body piercing jewelry), watches, eyeglasses, hearing aids, or dentures.
  • Ask the patient if he feels claustrophobic in confined spaces. Obtain an order for an antianxiety medication as needed.
  • Explain that the test is painless, but the machinery may seem loud and frightening and the tunnel confining. Tell the patient that he’ll receive earplugs for the noise, but he’ll be in constant communication with the technician.
  • Provide sedation, as ordered, to promote relaxation during the test.
  • Encourage the patient to resume normal activities, as ordered.

Diagnostic tests for Neurologic Disorders: Positron emission tomography

PET provides colorimetric information about the brain’s metabolic activity by detecting how quickly tissues consume radioactive isotopes. This technology can help reveal cerebral dysfunction associated with tumors, seizures, TIAs, head trauma, some mental illnesses, Alzheimer’s disease, Parkinson’s disease, and MS. (See Neuroimaging and Alzheimer’s disease.) In addition, a PET scan can help evaluate the effect of drug therapy and neurosurgery.

Inject, scan, and translate

In PET, a technician administers a radioactive gas or an I.V. injection of glucose (or another biochemical substance) tagged with isotopes, which act as tracers. The isotopes emit positrons that combine with negatively charged electrons in tissue cells to create gamma rays. After the scanner registers the gamma rays, a computer translates the information into patterns that reflect cerebral blood flow, blood volume, and neuron and neurotransmitter metabolism.

Neuroimaging and Alzheimer’s disease

Diagnostic tests for Neurologic Disorders

 

Nursing considerations

  • Assure the patient that the test won’t expose him to dangerous levels of radiation.
  • Explain that the test may require insertion of an I.V. catheter.
  • Encourage the patient to resume normal activities, as ordered.

Diagnostic tests for Neurologic Disorders: Skull and spinal X-rays

Typically, the skull X-ray is taken from two angles: anteroposterior (AP) and lateral. The practitioner may also order other angles, including Waters’ view to examine the frontal and maxillary sinuses, facial bones, and eye orbits and Towne’s view to examine the occipital bone. Skull X-rays help detect:

  • fractures
  • bony tumors or unusual calcifications
  • pineal displacement (indicates a space-occupying lesion)
  • skull or sella turcica erosion (indicates a space- occupying lesion)
  • vascular abnormalities.

Is your spine fine?

If the practitioner suspects spinal disease or an injury to the cervical, thoracic, lumbar, or sacral vertebral segments, he may order AP and lateral spinal X-rays. Depending on the patient’s condition, he may also order special angles such as the open-mouth view (to confirm odontoid fracture). Spinal X-rays help detect:

  • spinal fracture
  • displacement and subluxation (partial dislocation)
  • destructive lesions (such as primary and metastatic bone tumors)
  • arthritic changes or spondylolisthesis
  • structural abnormalities (such as kyphosis, scoliosis, and lordosis)
  • congenital abnormalities.

Nursing considerations

  • Reassure the patient that X-rays are painless.
  • Administer an analgesic before the procedure, as ordered, if the patient has existing pain so he’ll be more comfortable.
  • Remove a cervical collar if cervical X-rays reveal that no fracture is present and the practitioner orders it.
  • Encourage the patient to resume normal activities, as ordered.
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Diagnostic tests for Neurologic Disorders: Angiographic studies

Angiographic studies include cerebral angiography and digital subtraction angiography (DSA).

Diagnostic tests for Neurologic Disorders: Cerebral angiography

For cerebral angiography, the radiologist injects a radiopaque contrast medium, usually into the brachial artery (through retrograde brachial injection) or the femoral artery (through catheterization). This procedure highlights cerebral vessels, making it easier to:

  • detect stenosis or occlusion associated with thrombi or spasms
  • identify aneurysms and arteriovenous malformations (AVMs)
  • locate vessel displacement associated with tumors, abscesses, cerebral edema, hematoma, or herniation
  • assess collateral circulation.

Nursing considerations

  • Explain the procedure to the patient and answer his questions.
  • Confirm that he isn’t allergic to iodine or shellfish. (A patient with these allergies may have an adverse reaction to the contrast medium and require premedication with corticosteroids.)
  • Tell him that he’ll need to lie still during the p rocedure.

Feel the burn

  • Explain to the patient that he’ll probably feel a flushed sensation in his face as the dye is injected.
  • Maintain bed rest, as ordered, and monitor his vital signs and LOC.
  • Monitor the catheter injection site for signs of bleeding.
  • Monitor vital signs frequently for signs of internal bleeding.
  • As ordered, maintain pressure over the injection site.
  • Monitor the patient’s peripheral pulse in the arm or leg used for catheter insertion (mark the site).
  • Unless contraindicated, encourage the patient to drink more fluids to help flush the dye from his system.
  • Monitor the patient for neurologic changes and such complications as hemiparesis, hemiplegia, aphasia, and impaired LOC.
  • Monitor for an adverse reaction to the contrast medium, which may include restlessness, tachypnea and respiratory distress, tachycardia, facial flushing, urticaria, and nausea and vomiting.

Diagnostic tests for Neurologic Disorders: Digital subtraction angiography

Like cerebral angiography, DSA highlights cerebral blood vessels. Using a special type of computerized fluoroscopy, a technician takes an image of the selected area, which is then stored in the computer’s memory. After administering a contrast medium, the technician takes several more images. By manipulating the two sets of images, the computer produces high-resolution images for interpretation. Although arterial DSA requires more contrast medium than cerebral angiography, because it’s injected I.V., DSA doesn’t increase the patient’s risk of stroke and can be performed on an outpatient basis.

Nursing considerations

  • Confirm that the patient isn’t allergic to iodine or shellfish. (A patient with these allergies may have an adverse reaction to the contrast medium and require premedication with corticosteroids.)
  • Determine if the patient is taking any anticoagulant or antiplatelet medications; he’ll need to stop taking these drugs for a period of time before the procedure.
  • Restrict the patient’s consumption of solid foods for 4 hours before the test.
  • Explain that the test requires insertion of an I.V. catheter.
  • Tell him that he must remain still during the test.
  • Explain that he’ll probably feel a flush or have a metallic taste in his mouth as the contrast medium is injected.
  • Tell the patient to alert the doctor immediately if he feels discomfort or shortness of breath.
  • After the catheter is removed, encourage the patient to resume his normal activities.
  • Encourage him to drink more fluids for the rest of the day to help flush the contrast medium out of his system.

Diagnostic tests for Neurologic Disorders: Electrophysiologic studies

Electrophysiologic studies are commonly performed and include EEG and electromyography.

Diagnostic tests for Neurologic Disorders: Electroencephalography

By recording the brain’s continuous electrical activity, EEG can help identify seizure disorders, head injuries, intracranial lesions (such as abscesses and tumors), TIAs, stroke, or brain death. In EEG, electrodes attached to standard areas of the patient’s scalp record a portion of the brain’s activity. These electrical impulses are transmitted to an electroencephalogram, which magnifies them 1 million times and records them as brain waves on moving strips of paper.

Nursing considerations

  • Tell the patient that during the EEG, he’ll be positioned comfortably in a reclining chair or on a bed.
  • Explain that a technician will apply paste and attach electrodes to areas of skin on the patient’s head and neck after these areas have been lightly abraded to ensure good contact.
  • Explain that he must remain still throughout the test.
  • Discuss any specific activity that the patient will be asked to perform, such as hyperventilating for 3 minutes or sleeping, depending on the purpose of the EEG.
  • Use acetone to remove any remaining paste from the patient’s skin.
  • Encourage him to resume his normal activities, as ordered.

Diagnostic tests for Neurologic Disorders: Electromyography

Electromyography records a muscle’s electrical impulses to help distinguish lower motor neuron disorders from muscle disorders — for example, amyotrophic lateral sclerosis (ALS) from muscular dystrophy. It also helps evaluate neuromuscular disorders such as myasthenia gravis. In this test, a needle electrode is inserted percutaneously into a muscle. The muscle’s electrical discharge is then displayed and measured on an oscilloscope screen.

Nursing considerations

  • Tell the patient that the test may take 1 hour to complete and that he may be asked to sit or lie down during the procedure.
  • Warn him that he’ll probably feel some discomfort when the doctor inserts a needle attached to an electrode into his muscle and when a mild electrical charge is delivered to the muscle.
  • Explain that he must remain still during the test except when asked to contract or relax a muscle.
  • Explain that an amplifier may emit crackling noises whenever his muscle moves.
  • Encourage him to resume his normal activities, as ordered.
  • Explain why he shouldn’t take any stimulants, depressants, or sedatives for 24 hours before the test.
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