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Neurophysiology & Nerve Conduction Studies

By Liji Thomas, MD

Neurophysiology is a discipline within the health sciences which deals with the measurement and assessment of nervous system function rather than the anatomy of the nervous system. It helps to diagnose and monitor the progress of nervous disorders.

Neurophysiological assessment is performed via electrodes attached to the patient’s skin, and in many cases the patient’s cooperation is essential.

Clinical neurophysiology is a branch of this discipline which is hospital-based, and has to do with measuring neurological parameters, in a research setting, at the patient’s bedside, in intensive care units, or in a dedicated hospital laboratory. Clinical neurophysiologists test and record the function of the brain, spinal cord, spinal nerve roots, peripheral nerves (sensory and motor) and muscles, to help diagnose various disorders of the nervous system. They may use computerized imaging, magnetic, electrical, or electronic ways to record nervous activity, nerve impulse conduction, and coordination with the muscular response.

Some conditions in which this is useful include epilepsy, Parkinson’s disease, and motor neuron disease.

Tests used in neurophysiology

Diagnostic evaluations undertaken in the department of neurophysiology include:

  1. Electroencephalogram (EEG)
  2. Evoked Potentials (EPs)
  3. Nerve conduction studies (NCS)
  4. Electromyography (EMG)

Electroencephalogram (EEG)

The EEG is a record of brain function. Electrodes are attached to the scalp in various areas, corresponding to the lobes of the brain, to pick up the electrical potentials from the cortex of the brain. This is of particular use in patients suffering from epilepsy.

Evoked potentials (EPs)

Evoked potentials occur in response to a visual stimulus. They are of use mainly in nervous diseases such as optic neuritis or multiple sclerosis.

Nerve conduction studies

In many conditions it is necessary to test the way the peripheral nervous system functions, by measuring the speed of passage of nerve impulses through the motor and sensory nerves. This is by recording the effect of applying a small electrical current to the nerves to be tested.

The test, also called a nerve conduction velocity test, helps to determine if the nerve has been damaged or destroyed.

Surface patch electrodes are attached to the skin. One supplies stimulation to the nerve. The other records the resulting nerve impulse. The speed of conduction is calculated using the distance between the electrodes and the time gap between the stimulation and the arrival of the resultant electrical impulse at the other electrode. Each nerve is tested separately.

Electromyography

Electromyography is a related test which inserts slender electrodes into the voluntary muscles, to diagnose conditions such as motor neuron disease and radiculopathy. It measures the electrical activity in the muscle fibers, and shows if the muscles or nerves are damaged, and if so, to what extent and at what location.

More specialized tests in neurophysiology include:

  1. Ambulatory EEG for long-term monitoring
  2. Video telemetry
  3. Sleep studies
  4. Monitoring patients during neurosurgical procedures, such as scoliosis surgery, where the spinal cord integrity has to be mapped throughout
  5. Tests of visual neuron functioning

Neurophysiologists may develop a greater interest in specific areas such as epilepsy and its origin as well as corrective surgery, Parkinson’s disease and sub-thalamic nuclear ablation, and mapping the cortex in various disorders.

The responsibilities of a neurophysiologist include supervising and supporting technicians in the wards, operation theaters, and departmental laboratories. They must report EEGs and interpret EMGs to diagnose various neuromuscular conditions.

References

  1. https://www.healthcareers.nhs.uk/explore-roles/medicine/clinical-neurophysiology
  2. http://jnnp.bmj.com/content/76/suppl_2/ii23.full
  3. https://www.uclh.nhs.uk/OurServices/ServiceA-Z/MEDSPEC/NPHYS/Pages/Home.aspx
  4. http://www.uhs.nhs.uk/OurServices/Brainspineandneuromuscular/NeuromuscularWERMANS/Diagnosisandtreatment/Nerveconductionstudiesandelectromyography.aspx
  5. http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/nerve_conduction_velocity_ncv_92,P07657/

Further Reading

    Last Updated: Oct 31, 2016

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