Introduction
Electroneurography (ENG) is a neurological diagnostic method that determines the ability of nerves to transmit electrical impulses and thus to excite a muscle, for example. This technique allows nerves to be stimulated and their electrical activity to be conducted superficially so that more precise statements can be made about the neurological basis of a patient’s complaints. This measurement is used to determine the nerve conduction velocity (NLG) and thus the length of time it takes from the excitation of the nerve to the response, for example in the form of a muscle twitch of a muscle that is supplied by the nerve.
For a nerve to be able to transmit normally, both the nerve itself (axon) and the sheath around the nerve (myelin sheath) must be intact. In the clinic, electroneurography is used to check the functional state of nerves. This can be necessary in a wide variety of diseases.
In addition, electroneurography can be used to distinguish whether the patient’s symptoms are due to nerve damage or muscle damage. Finally, electroneurography is used to classify nerve damage (degeneration) precisely in order to follow the healing process after nerve damage.
- Accidents of all kinds, for example cuts
- Incarcerations for example carpal tunnel syndrome
- Damage to nerve fibers (axons)
- After alcohol abuse (polyneuropathy)
- Damage to the surrounding shell (myelin), for example in diabetes (diabetic neuropathy),
- Damage to the transmission between nerve and muscle, for example myasthenia gravis.
A single nerve consists of many nerve fibers.
These can be motor (for movement), sensory (for feeling) or autonomous (involuntary activities such as digestion). Most nerves in our body consist of these three types of nerves. However, the nerves important for electroneurography are mostly purely motor or purely sensory.
In general, nerves are distinguished according to the size or diameter of the nerve fiber and whether the nerve is additionally isolated (myelinated). In general it can be said that nerves with a larger diameter conduct electrical impulses faster and nerves with insulation also conduct electrical current faster. In both cases, this leads to a faster reaction of the area supplied by the nerve, for example, if you painfully burn your finger on the hotplate (sensory) and then pull your hand away (motor).
In electroneurography, various parameters are recorded. In general, a distinction is made between the examination of motor and sensory nerves. Only nerves whose electrical potential change can be detected on the surface by electrodes can be examined, since deeper needle electrodes are almost never used for electroneurography.
Electroneurography of motor nervesElectroneurography of motor nerves is often performed. Motor nerves include those that run from the brain to muscles and are responsible for controlling the movements of the body. When a motor nerve is examined, the nerve is stimulated by a skin electrode, whereupon it is discharged (depolarized) and this electrical voltage difference spreads in both directions of the nerve.
If the nerve and the supplied muscle are intact, the muscle will contract. This time span is only a few milliseconds and is measured from the time difference in voltage between the first and second electrode and compared with values from healthy subjects using a target scale. In addition to the time elapsed from the stimulation of the nerve to the contraction of the muscle (nerve conduction velocity), electroneurography often measures the strength of the muscle contraction as well as the strength of the electrical potential arriving at the muscle.
2. electroneurography of sensitive nervesSensitive nerves, on the other hand, transmit stimuli from the skin to the brain, for example, so that we know when an object is too hot and we can burn ourselves. This perception in the skin takes place through sensory cells that are linked to nerves, which in turn transmit the signal to the brain. To examine the function of sensitive nerves, a certain area of skin is stimulated and irritated by a superficial skin electrode.
The irritation of the skin causes an electrical impulse to be detected along the nerve in healthy volunteers, which in turn transmits this sensation to the brain.For this reason, a second electrode can be used to determine a change in voltage along the nerve and also to calculate the nerve conduction velocity and the strength of the signal. Electroneurography has almost no side effects. It is therefore considered a low-risk routine procedure, which is performed very frequently every day.
Some patients find the electrical stimulation of the nerves unpleasant or slightly painful. In most cases the nerve conduction velocity is measured by means of adhesive electrodes applied to the skin. Attaching these electrodes is painless.
Under certain circumstances, however, an allergic reaction to the adhesive may occur, especially in patients with patch allergy. However, permanent damage cannot occur if the voltage is correct. Special care must be taken with patients with pacemakers. In this case, it should be carefully considered whether the examination is urgently necessary or whether it could also be used by another examination procedure.
