ELECTRONEUROGRAPHYElectrophysiological Principals involved

And

Clinical Diagnosis

Presented by :

SARA SIDDIQUI

Course no. 656

ELECTRONEUROGRAPHY:

Electroneurography is a non invasive, electro neurological diagnostic test to measure the conduction velocity and latency of peripheral nerves.

It is the most accurate test for detecting and locating peripheral nerve injury of about 100 kinds of peripheral neuropathies.

Such as Diabetic polyneuropathy, Gullain-Barre syndrome, Carpel tunnel syndrome, thoracic outlet syndrome

Working Principal:

Conduction velocity is the rate of propagation of nerve impulse (action potential) along a nerve fiber.

NCV determine the distance covered by AP per unit time, NCV = lambda /time

Factors affecting NCV:

1. Diameter of the axon

Different peripheral nerve fibers have different diameters and thus conduction velocity of their own. AP recorded are Compound AP.

2: MYELINATION:

Myelination induces insulation around the fiber except small points known as nodes of Ranvier

Thereby increases resistance across membrane Rm but decreases its capacitance Cm

AP are saltatory in nature

Other Factors

Temperature as proportional to velocity External resistance Rl Density of gates Ions concentrations Anesthetics Anoxia

HOW THE TEST IS PERFORMED STRONG BUT BRIEF STIMULATION AT ONE POINT UNDER THE

SKIN AND AT THE SAME TIME RECORDING THE ELECTRICAL ACTIVITY AT ANOTHER POINT OF NERVE TRAJECTORY IN THE BODY.

The response is displayed on the video monitor of computer or cathode ray tube.

The stimulus and recordings are carried out by the surface or disc electrodes which are placed over the skin after applying the conducting gel.

Stimulus is felt as the electrical shock thus may be painful.

Thoracic Outlet Syndrome

Observations And Diagnosis:

Sometimes EMG is combined with ENoG for accurate diagnosis called as electromyoneurography

Any decrease in the NCV will indicate:

1.Extent of demyelination of nerve

2. Any Conduction Block

3.Axonopathy (damage to the long

portion of a nerve cell)

CLASSIFICATION OF PERIPHERAL NEUROPATHIES:

References:

Neurophysiology:

3rdedition by R.H.Carpenter

Nerve Conduction studies: https://backyardbrains.com/experiments/com

paringNerveSpeed https://Hmphysiology.blogspot.com

peripheral neuropathy: Physical medicine and rehabilitation Board

review – Sara Cuccuvullo MD

For Further Reading:

http://openwetware.org/wiki/Lab_9:_Conduction_Velocity_of_Nerves

http://www.neurolist.com/site/emg_case.htm

Happy Reading !