6 Neurologic Diagnostic Tests

Purpose and general safety

Neurologic tests help identify problems involving the brain, spinal cord, nerves, muscles, and cerebral blood vessels. Preparation and aftercare depend on the test. Follow the ordering clinician’s and testing facility’s instructions; do not stop medicines or change food or fluid intake unless specifically directed.

Diagnostic findings support, but do not replace, clinical assessment. A normal result on one test may not exclude disease.

Lumbar puncture and cerebrospinal fluid

A Lumbar puncture (LP), also called a spinal tap, collects Cerebrospinal fluid (CSF) from the lower spinal canal. It can help investigate infection, bleeding, inflammation, and other neurologic disorders. The clinician may also measure CSF opening pressure.

Preparation and procedure

Explain the purpose and steps, obtain consent as required, and provide privacy and positioning support. Review medicines—especially anticoagulants or antiplatelet drugs—bleeding history, allergies, and relevant medical conditions. Do not withhold prescribed medicines without an order.

Assess neurologic status and consider whether imaging is needed first. An LP may be unsafe when there is concern for a mass causing increased intracranial pressure, significant bleeding risk, or infection at the puncture site. The clinician determines whether the benefits outweigh the risks.

The patient is usually positioned on the side with the back flexed, or sitting and leaning forward. Remaining still helps the clinician collect the sample safely.

Aftercare and complications

Monitor the puncture site, symptoms, and vital signs as indicated. Follow local instructions about activity; strenuous activity is often avoided for the rest of the day. Routine prolonged bed rest has not been shown to prevent headache. Encourage fluids if allowed, but hydration is not a guaranteed way to prevent headache.

A Post-dural puncture headache may worsen when upright and improve when lying down. Other possible complications include local soreness, bleeding, infection, CSF leakage, or—rarely—nerve injury. Promptly report severe or persistent headache, fever, new weakness or numbness, increasing back pain, or fluid or blood leaking from the site.

Common CSF findings

Interpret results together with symptoms, blood tests, and laboratory reference ranges. Typical adult CSF is clear, has very few white blood cells (often $0\text{–}5$ per microliter), and has no red blood cells. Reference ranges vary by laboratory.

• Increased white cells, especially neutrophils, together with increased protein and decreased glucose can support bacterial meningitis. Interpret these results with cultures and clinical findings.

• Increased lymphocytes, often with normal glucose and normal or mildly increased protein, can occur with viral meningitis.

• Red blood cells or xanthochromia (yellow-tinged fluid) may indicate bleeding into the CSF, but a traumatic tap can also introduce blood. Interpret the full sample series and clinical picture.

• Increased protein with few white cells can occur in Guillain–Barré syndrome, among other conditions.

• Oligoclonal bands may support multiple sclerosis when considered with other evidence.

Electroencephalography

Electroencephalography (EEG) records electrical activity from the brain using electrodes attached to the scalp. It is used to evaluate suspected seizures, altered consciousness, and some sleep or brain-function disorders. A routine EEG is painless and does not deliver an electrical shock.

Preparation and safety

Wash the hair and avoid oils, gels, or sprays so the electrodes adhere well. The facility may ask the patient to avoid caffeine or sleep less than usual before a particular EEG; follow the test-specific directions. Do not stop seizure medicines or other medications unless the prescriber instructs you to. Tell staff about recent seizures, medicines, and any planned sleep deprivation.

During the test, the patient may be asked to breathe deeply or look at flashing lights; these procedures can sometimes provoke symptoms. Staff monitor the patient and can respond if a seizure occurs. For an ambulatory or video EEG, follow instructions for the recorder, activity, and event diary.

Aftercare and interpretation

After a routine EEG, the patient can generally return to usual activities. If sleep deprivation or sedation was used, follow instructions about driving and supervision. Remove electrode paste as directed.

A normal EEG does not rule out epilepsy because abnormal electrical activity may not occur during the recording. Epileptiform discharges can support a seizure disorder, while slowing may indicate generalized or localized brain dysfunction. Findings must be interpreted with the history and observed events; EEG alone does not diagnose every cause of a seizure-like episode.

Brain imaging and vascular tests

CT and MRI

Computed tomography (CT) uses x-rays and is often used when rapid imaging is needed, such as for suspected acute bleeding or head injury. Magnetic resonance imaging (MRI) uses a strong magnetic field and radio waves and can show detailed brain and spinal cord structures. CT angiography (CTA) and MR angiography (MRA) assess blood vessels; MRA may sometimes be performed without contrast.

Before imaging, confirm the patient’s identity and the requested test. For CT or CTA, ask about possible pregnancy, prior contrast reactions, kidney disease, and any facility-specific preparation. For MRI, carefully screen for implants, devices, and metal, including possible metal fragments in the eyes. Do not enter the MRI room with unapproved metal or equipment. Tell staff about claustrophobia, pregnancy, or a possible need for sedation. After sedation, follow recovery and driving instructions. After contrast, report trouble breathing, hives, or other signs of an allergic reaction immediately.

CT uses ionizing radiation; MRI does not. Both can produce images that help identify abnormalities such as bleeding, tumors, stroke, or structural changes, but precise findings depend on the test and timing. Contrast-enhanced tests can carry risks, including uncommon allergic-like reactions; clinicians assess relevant history and kidney function as appropriate.

Cerebral angiography

A Catheter-based cerebral angiogram uses x-ray imaging and contrast injected through a catheter to show brain blood vessels. It may identify an aneurysm, narrowing, blockage, or vascular malformation. Before the procedure, review allergies or prior contrast reactions, kidney problems, bleeding history, and medicines; fasting and blood tests may be ordered.

Afterward, monitor the access site for bleeding or swelling and check circulation and neurologic status as directed. Follow instructions about keeping the access-site limb still and resuming activity. Possible complications include bleeding or bruising, contrast reaction, kidney injury, and—rarely—stroke or vessel injury. New weakness, numbness, speech or vision changes, or uncontrolled bleeding requires urgent attention.

Nerve and muscle testing

Nerve conduction studies (NCS) use small electrical pulses to measure how quickly and strongly nerves conduct signals. Electromyography (EMG) uses a small needle electrode to record electrical activity in selected muscles. Together, these tests help evaluate disorders of peripheral nerves, nerve roots, and muscles.

Keep the skin clean and free of lotions or creams, and wear clothing that gives access to the area being tested. Tell the clinician about blood thinners, bleeding problems, pacemakers, or other implanted electrical devices. NCS may cause brief tingling or discomfort; EMG can cause temporary muscle soreness or small bruises.

Abnormal conduction or muscle activity can help localize nerve or muscle dysfunction, but results are interpreted alongside symptoms and examination findings.

Applying results and aftercare

Preparation is test-specific: review medicines and risks, follow facility instructions, and never stop prescribed medication without direction. Aftercare includes observing for test-related complications and giving clear instructions about when to seek help.

Urgent symptoms include new weakness or numbness, speech or vision changes after cerebral angiography, uncontrolled bleeding, and the specified warning signs following a lumbar puncture. Follow the care team’s instructions about activity, supervision, and recovery after each test.