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Neurological tests (CT scan, MRI, ECG, angiography, Xray, Electromyogram)

Neurological tests are some of the most common tests done throughout the world. Nervous system constitutes a major part of the body and its correct functioning is essential for the maintenance of quality of life.

A number of disorders affect the mind, cerebral cortex, cerebellum, peripheral nerves and all associated parts of central, peripheral and autonomic nervous system and it is their coordinated efforts which sustain a person.

When a patient presents with any neurological disorder it is essential to take a thorough history as to when the patient was alright and how the disease started, whether it is stationary or progressive.

Site and nature of neurological deficit must be found out. A detailed physical examination along with that of nervous system must be carried out to arrive at the diagnosis.

Once clinical diagnosis has been arrived at, a number of tests may be done to confirm the diagnosis. Medical science has advanced rapidly during the last few decades and we have now a number of newer techniques to arrive at the diagnosis.

Neurological tests (CT scan, MRI, ECG, angiography, Xray, Electromyogram)

Various Neurological tests involved in Investigation

Various tests in this are:

Electroencephalogram

The electrical activity of the brain is recorded by use of electrodes placed at various sites in the skull. These are usually in the order of from 5 to 50 millivolts and have a duration of from one second to 20 milliseconds. Recording is done on a 16 channel recorder for 10-30 minutes.

Various waves are recorded. The area of alpha discharge is usually limited to parieto occipital region. These waves wax and wane spontaneously and usually disappear when the patient opens his or her eyes or fixes his or her attention somewhere.

Waves faster than 13 Hz and of lower amplitude are called beta waves and are recorded from frontal region while very slow waves are called delta waves and are absent in normal record. EEG is of use in cases of epilepsy, seizure, coma and space occupying lesions.

Electromyogram (EMG)

This involves recording electrical activity of nerve and muscles. It involves inserting a needle in a skeletal muscle and changes produced during relaxation and physical activity are recorded either on a magnetic tape or on paper EMG is of use in cases of muscle disorders like myopathy, motor neuron disease.

In addition to conventional recording with electrodes, specialized techniques are used to record activity of single muscle fibers or of the entire motor unit.

Nerve conduction studies

These are of value in cases of neuropathies and where there is local compression of nerve. The speed of conduction in motor and sensory peripheral nerves is recorded after electrical stimulation of nerve. The whole process involves measurements of latencies for F responses (motor action potential). Sensory action potentials (H. reflexes) and blink reflexes.

Evoked potentials

These are records of electrical activity produced by groups of neurons within the eye, brain stem, spinal cord, thalamus or cerebral hemisphere and are caused by visual, auditory, tactile or other sensory stimuli. The amplitude of these potentials is recorded by EEG electrodes.

Evoked potentials provide sensitive objective extension of clinical symptoms and are useful in various neurological disorders. Visual evoked potentials are useful in cases of retrobulbar neuritis, Frederich ataxia while auditory evoked potentials help in diagnosing acoustic neuroma and somato sensory evoked responses help in diagnosing sensory peripheral neuropathy, tabes dorsalis, sub acute combined degeneration of cord.

Evoked response document lesions in various pathways and may be used to quantify improvement in patient’s therapy.

Radiological studies

X-ray skull is often done as a routine. Its main use is in detecting enlargement or destruction of Sella turcica (tumors raised intracranial tension) calcification (tubuerculoma, cysticercosis, pineal calcification) and presence of erosion (metastasis, myeloma).

Computed tomography (CT scanning)

It is a very important and useful test. It is safe and does not cause much inconvenience. CT is used in the diagnosis of space occupying lesion, cerebral hemorrhage (intracerebral and subarachnoid) cerebral atrophy etc.

The image can also be enhanced by use of intravenous contrast media to delineate areas of increased blood supply and edema more clearly.

Main drawback to CT scan is that lesions below one cm in diameter may not be seen in the study.

Magnetic resonance imaging (MRI)

MRI is useful technique by making use of the principle that all nuclei when bombarded with radio frequency waves at right angles generate images. It is useful in detecting cases of demyelinating diseases, arteriovenous malformations. Congenital and developmental anomalies, posterior fossa vascular tumors, metastasis, tuberculoma, cysticercosis and lesions which are likely to be missed by CT scanning. Its particular value is in distinguishing between white and grey matter.

Myelography

A myelogram is sometimes required to demonstrate site of spinal tumor. A radio-opaque dye (Myodil) is injected via lumbar puncture needle and conventional X-rays or CT myelogram recorded. It is also useful in cases of cervical spondylosis where an MRI may not be able to demonstrate a lesion.

Cerebral angiography

A contrast is injected either into the carotid or vertebral artery and serial films by a rapid cassette changer are taken and abnormalities in the arterial and venous vessels of the brain like cerebral artery occlusion, arterio venous fistula and aneurysm are visualized.

Digital subtraction angiography (DSA) is comparatively safe procedure. Here contrast is injected intravenously while in angiography, procedure is invasive and dye has to be injected intraarterially.

Isotopic brain scanning. Isotopic imaging and flow studies of the brain are usually done in diagnosing vascular tumors, cerebral infarcts, subdural haematoma etc. These studies are more time consuming and incidence of false positive results is high.

Isotopic brain scanning has been largely replaced by CT scan and MRI.

Biopsy. Muscle and nerve biopsies are done in cases of myopathies and polyneuropathy to establish the diagnosis.

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