Neurological Investigations

Neurological investigations like any other medical investigations complement the clinical evaluation and help in arriving at the final precise diagnosis. There are myriad neurological disorders and correspondingly there are large number of neuro investigations too. These tests help in confirming the clinical suspicion about a disease of the nervous system by either ruling it in or ruling it out, for example if there is a clinical suspicion of meningitis in a patient then a CSF (Cerebro Spinal Fluid)test can either rule in the possibility of meningitis or rule it out.

Before the advent of tests like CT or brain MRI, many times it was really difficult to arrive at a firm neuro diagnosis; and now the availability of these investigations has phenomenally catapulted the abilities of a Neurologist in resolving a patient’s symptoms and clinching the final diagnosis.

Of course developments have happened not just in radiological realm of investigations (CT, MRI etc), but also in almost other areas including blood & CSF tests, sleep studies etc.

In this article let us review some of these routinely performed neurological investigations in the field of neurology.

• Blood tests
• Lumbar puncture (spinal tap)
• EEG
• EMG (electromyography) & Nerve conduction studies
• Sleep studies
• Evoked potentials
• X-ray
• CT
• MRI
• Biopsy (muscle, nerve, brain etc)
• Angiograms etc.

Blood tests:

These tests may look quite basic at times, but in reality many times they hold a huge role while investigating a case. For example blood tests like fasting glucose, HbA1c help in diagnosing diabetes. Poorly controlled diabetes is a cause for neurological disorders like stroke, neuropathy etc. This is just one example and there are myriad blood tests that are used as neurological investigation almost every day while chasing after a neurological condition like dementia, stroke, encephalopathy etc.

Lumbar puncture (spinal tap):

This procedure takes out CSF (cerebrospinal fluid) from the lower back area. There are certain absolute or relative contraindications for this test (e.g. bleeding disorder).

Indications (diagnostic);

• Neuro infections (e.g. encephalitis, meningitis)
• Demyeliating conitions like MS (Multiple sclerosis)
• SAH (Sub-arachnid hemorrhage)
• Pseudotumor cerebri etc.

Indications (therapeutic);

• Administration of anti-cancer drugs to CSF
• Administration of antibiotics to CSF
• Drainage of CSF for normal pressure hydrocephalus, pseudotumor-cerebri etc

Procedure: A sterile needle is inserted into the lower back area, usually at L3-4; L2-3, L4-5, L5-S1 levels are other options.

This test is performed by Neurologists and certain other physicians very frequently and majority of the times no complications are encountered. However rarely complications like bleeding, infections are encountered. Brain herniation is a very grave complication but very rarely encountered. Spinal headache is common but usually relieved with pain killers, caffeine, fluids, lying flat etc; rarely an epidural blood patch may be necessary.

Spinal tap & EMG are considered as the two painful neurological investigations. Local anesthesia takes care of pain during spinal tap. Reassurance during the test is all needed with the EMG test most of the times.

EEG (Electro Encephalogram):

EEGs are one of the most commonly performed neurological investigations and they provide information on the functional aspect of the brain unlike the structural tests like CT etc. This test captures patient’s certain brain activities and they are analyzed.

Some indications include:

• Epilepsy (seizure disorder)
• Altered sensorium (change in mental status
• Dementing illness (e.g. Creutzfeldt Jacob disease)
• Brain death evaluation

Procedure: Multiple electrodes are attached to the scalp area and a continuous record of about 20 to 30 minutes is done. During the test you may be asked to open and close eyes, breath deep and rapid (hyperventilate) etc. The technician may also flash a light source (photic stimulation) in front of you.

There are different types including routine, ambulatory (24 to 72 hours), video-EEG etc.

Sleep studies (Polysomnography):

These tests are becoming increasingly popular neurological investigations as doctors are realizing the negative health impact of a condition called as OSA (obstructive sleep apnea). During the test your sleep-activities are recorded and analyzed.

Some indications include:

• OSA (obstructive sleep apnea/hypopnea)
• Narcolepsy

Procedure: The test is performed in a sleep lab. During the procedure you are hooked up with myriad electrodes such that your brain waves, breathing pattern, muscle tone, eye movements etc can be captured and interpreted. If a condition called narcolepsy is suspected; then the following day you may also under go another test named as multiple sleep latency test (MSLT) during which you will take several scheduled naps.

Electromyography/ Nerve Conduction Studies (EMG/NCS):

Generally considered as one of the most feared neurological investigations by the patients, these tests are however invaluable in making a neuromuscular diagnosis. The test involves electrical shocks and a needle insertion to muscles. Frequent reassurance is all that is necessary most of the times for a patient to successfully undergo this test.

Some indications include:

• Neuropathies (nerve damage)
• Myopathies (muscle damage)
• Radiculopathies (pinched nerve) etc.

Procedure: Most often the electrical stimulation of the nerves is accomplished first. Electrodes are placed over certain pre-designated points over the nerves and are stimulated. The electrical responses produced by nerve and/or muscle are recorded and interpreted. During the 2nd part a fine needle may be inserted in to the muscle and additional studies are conducted.

Evoked potentials:

With the advent of MRI these neurological investigations are falling out of favor to some extent however indications still exist. With this procedure the integrity of the sensory pathways that connect the periphery with the brain is studied.

An important indication for this test is MS (Multiple sclerosis) especially the visual evoked potentials. Tests like VEP & BAER are also used for the evaluation of certain blind and deaf situations.

Procedure:

SSEP (somatosensory evoked potentials): You are hooked up with varieties of electrodes over the scalp, spine, shoulder etc at pre-determined sites. They are connected to equipments which amplify and measure your minute brain activities called evoked potentials. Stimulation is usually done over the limbs.

VEP (visual evoked potentials): You are hooked with several electrodes and then asked to se a checkerboard patterned or flashing light in front of you.

BAER (brainstem auditory evoked potentials): With this one after you are hooked up with several electrodes auditory stimulation is given through earphones (click or tone stimulus).

X-ray:

This basic radiological procedure is occasionally still used during neurological investigations like spine or skull fractures. In general CT or MRI has supplanted this test

Pregnancy is generally a contraindication. Excessive exposure to x-rays can cause tumors.

CT or CAT scan:

This advanced x-ray procedure is frequently utilized by neurologists. MRI is generally regarded superior to CT scan in the neurology field but is not always true; a CT is more sensitive for detecting many bleeding conditions. It is cheaper and more easily available as compared to MTR. Patients having certain metallic stuff in their body including heart pacemaker etc cannot undergo MRI, but CT is ok.

Its contraindications are similar to x-ray.

MRI (magnetic resonance imaging):

This is also a radiological test however it doesn’t employ ionizing radiation like x-ray or CT which is an advantage.

It indications are similar to CT in general. Although for majority of neurological diseases MRI is superior, but as noted above CT enjoys its own comfortable niche.

Some of the relative or absolute contraindications include, a metallic structure or devices in your body, pregnancy, especially the first trimester) & severe claustrophobia. Claustrophobic patients can undergo open MRI.

Both CT & MRI may be repeated after a contrast injection is given to enhance the detection of pathologies.

Biopsy test:

These are rarely performed neurological investigations (not ordered on a routine basis). Biopsy of brain, nerve or muscle is usually done. Biopsies of other tissues like skin, conjunctiva also accomplished sometimes depending upon what we are suspecting.

During the test a small piece of tissue is taken out and studied in the lab under the microscope.

Angiogram:

There are few different types of angiograms. These tests study the blood vessels like arteries with regard to any blockage (e.. cholesterol build up), aneurysm, dissection etc.

With the conventional type a contrast agent is injected in to a vein or artery then the blood vessel in question is studied. Tests like MRA (magnetic resonance angiogram) may not always require an injection. If the contrast agent is injected then risks of allergic reaction, kidney damage etc are of concern. Generally the Magnetic Resonance Angiogram (MRA) is less informative compared to the conventional type of angiograms but it is safer.