LEMG: Overview

Key Glossary Terms

Laryngeal Electromyography (LEMG)
A test that measures the electrical discharges from voice box muscles during activities such as speaking, breathing, and swallowing

Paresis
Partial paralysis; partial loss of nerve input to a muscle, resulting in muscle weakness

Paralysis
Complete loss of nerve input to a muscle, resulting in complete loss of muscle function

Motor Unit
The functional unit made up of all muscle fibers that receive nerve inputs from a single nerve cell; a muscle is made of many motor units

Glossary

LEMG is defined in three parts:

1. laryngeal = larynx (voice box)
2. electro = electrical signals
3. myo + graphy = muscles + recording

LEMG is the recording of the electrical discharges of voice box muscles. This specific information can help identify whether a voice disorder is due to partial or complete loss of nerve input to the voice box muscles. (For more information, see Vocal Fold Paresis/Paralysis.)

LEMG is a technique used to evaluate the way specific muscles in the larynx are working during particular types of tasks, such as taking a breath or producing voice. LEMG is a way of recording and observing the electrical discharges that are generated in specific muscles of the larynx. This information can be used, along with other information from other types of medical tests, to determine a diagnosis and treatment plan.

During LEMG, four muscles (two types on both sides of vocal folds) are tested. These tests give specific information about the two nerves connecting to voice box muscles: recurrent laryngeal nerve (RLN) and superior laryngeal nerve (SLN). (For more information, see Anatomy & Physiology of Voice Production.)

LEMG has been in use since the late 1950s and is based upon the principles of muscle function (physiology) and the techniques of electromyography that have been developed using other muscles of the body, such as leg and arm muscles.

• LEMG is a part of the investigation of voice disorders. LEMG results must be reviewed in conjunction with key findings obtained by the voice care team as part of a full evaluation of the voice box and voice.
• LEMG may be performed early in the investigation of a patient's voice disorder because LEMG results can inform:
  • The need for further testing
  • The types of tests needed
  • Decisions regarding the timing of surgery
• LEMG is often performed along with stroboscopy and voice recording. (For more information, see Laryngoscopy/Stroboscopy.)

LEMG is performed most often in voice centers, large medical centers, or clinics associated with a university hospital. Because LEMG is highly specialized, it is not available everywhere. The procedure is performed on an outpatient basis.

LEMG can be performed by:

• An ear, nose, and throat doctor (ENT, or otolaryngologist)
• An ENT who specializes in voice box disorders (laryngologist)
• A rehabilitation physician (physiatrist)
• A physician who specializes in the nervous system (neurologist)

Poor LEMG technique can cause errors: Like many other tests, LEMG requires practitioner skill and experience in proper technique and interpretation. Errors in the performance and interpretation of LEMG are usually the result of inappropriate techniques, such as poor electrode placement. Sometimes, lack of patient cooperation can also hinder the procedure.

Voice care team involvement. In leading voice centers, a team of doctors is involved in performing LEMG. Team members may include:

• Laryngologist
• Neurologist
• Non-medical doctorate professional with special training in the interpretation of electrical signals from muscles and nerves (electromyographer)