Magnetic resonance neurography

The electroneurography or electroneurography ( ENG) is a method of electrodiagnosis in neurology to determine the functional state of a peripheral nerve. It is recognized, among others, the nerve conduction velocities and their distribution, the amplitude and the refractory period.

Technology

The basic principle is to irritate a nerve (usually on the extremities ) by means of a short ( 0.1-2.0 ms) electrical pulse ( square wave ). This leads to depolarization of the nerve, which is passed in both directions over the nerve fiber (Axon ). The induced voltage change can then be measured along the nerve depending on the issue. In routine medical diagnostics such valuable information about the functional state of nerve and the location of a fault can be obtained. It is however always the sum response of many nerve fibers. By convention, therefore, the nerve conduction velocity of the fastest conducting fibers is given.

The conduction velocities of motor nerve fibers can be easily determined by stimulation of the nerve at two different locations and measuring the evoked responses in the muscle. There the difference in conduction times ( latency ), for example in ms and the difference of stimulus locations, for example in mm is determined. The knowledge of the distance and time difference allows the calculation of the nerve by forming the quotient distance / time.

The amplitude of the stimulus response gives a rough indication of the number of forwarding nerve fibers, but is also, among others, the position and shape of the contact electrode dependent.

By deriving the F- wave can be made for motor nerve statements about nerve conduction up to the soma of the nerve cell, which is for arm and leg nerves in the anterior horn of the spinal cord. The F- wave is a one of its fluctuating expression, late response potential of low amplitude that occurs after stimulation.

The H- reflex provides information about the condition of the spinal muscular proprioceptive reflex arc. He is the electrical equivalent of the mechanically induced using a reflex hammer reflex.

An A wave can show a lesion of nerves to the detected portion of the nerve.

After a depolarization of the nerve membrane, the initial state by active processes must first be restored until a new excitation of the membrane is possible. This time is called the refractory period. The determination of the refractory period gives important information on the functional state of the nerve.

Apparatus condition are adjustable according to a stimulator, a measurement system for the voltage memory, and an evaluation unit for the measurement of the recorded potentials. Such devices are available in many neurological departments and practices.

Electrical stimulation of the nerve is usually, sometimes perceived as unpleasant as painful from the examinee. The sensitivity is individually quite different.

Investigation target

Basically, the electroneurography for studying the function of these nerves is suitable enough run close to the surface, so that they can irritate both electrically as to derive a response potential. This is primarily for the nerves in the extremities.

The investigation is therefore indicated mainly to investigate damage to individual nerves ( for example, due to injuries in the context of an accident ), or general nerve damage ( polyneuropathy ).

It is possible to distinguish between damage to the myelin sheath ( the isolation of a single nerve fiber ), and damage to the axons ( nerve fibers themselves ) to be distinguished. Destruction of the myelin sheath performs impairment of saltatory conduction to reduce the nerve. In contrast, it is due to loss of axons in order to reduce the amplitude of the stimulus response. In many diseases, however, there will be two phenomena with emphasis on one aspect.

In hereditary or inflammatory conditions demyelinating nervous disease ( HMSN -I and Guillain -Barré syndrome and variants) is it damaging the myelin sheaths and consequently a reduction of nerve conduction velocities. In related diabetes mellitus neuropathy are mainly the myelin sheaths, mainly damaged axons in alcohol- toxic cause.

The series electrical stimulation of motor nerves allowed to investigate disorders of impulse transmission from nerves to skeletal muscles. When it comes myasthenia here, for example a decrease in the response in the course of 5-10 ( 3 / s ) is equal to severe irritation, which is called a decrement.

Related research

For a further assessment of motor nerves ( which control the muscles) is often a useful electromyography. To further assess the function of sensory nerves deriving evoked potentials required for the proximal portions and the forwarding of the spinal cord and brain.