Journal of Voice Vol. 6, No. 2, pp. 15%187 © 1992 Raven Press~ Ltd., New York Electromyography and Special Article Neurography in Neurolaryngology M. Nasser Kotby, *E. Fadly, tO. Madkour, M. Barakah, A. Khidr, *T. Alloush, and M. Saleh Unit of Phoniatrics and *Department of Neurology, Faculty of Medicine, Ain Shams University; and ?Department of Neurology, Faculty of Medicine, Cairo University, Cairo, Egypt Summary: Laryngeal electromyography (EMG) is an important tool in the study of laryngeal disorders. This review considers the current state of the art. The general principles of EMG and of the laryngeal neuromotor control system are reviewed. Important criteria for interpreting EMG characteristics, includ- ing the motor unit action potential and spontaneous activity, are considered in the context of several pathologic conditions. Technical and clinical difficulties are reviewed. Key Words: Electromyography--Potentials. Section I. General Principles of Electromyography and Neurography ELECTROMYOGRAPHY Electromyography (EMG) is the study of electri- cal potentials generated in a skeletal muscle. EMG offers a useful tool for the study of activity of the skeletal muscles in vivo. It also provides a diagnos- tic tool that helps evaluate neurogenic and myo- genic lesions of the skeletal motor system, and as- sists in monitoring the development and prognosis of these lesions. The diagnostic value of EMG is enhanced by the study of the condition of the motor and sensory nerves in response to electrical stimuli. The behavior of the nerves depends on the degree of the interruption of its course in the various le- sions and pathologies. It may also provide indica- tions of the restoration of function in a disrupted nerve. Address correspondence and reprint requests to Dr. M. Nasser Kotby, 11, E1 Ansary Street, Manshiet E1 Bakry, Cairo, Egypt. NEUROPHYSIOLOGICAL PRINCIPLES OF ELECTROMYOGRAPHY Normal findings in skeletal muscles During registration of the electrical activities of a normal skeletal muscle by needle electrodes, a se- ries of phenomena are observed: 1. Insertion potentials are heard as brief dis- charges (300 ms) of single muscle fiber potentials on the insertion of the needle electrode (1). 2. If the muscle is completely relaxed, these ini- tial transient potentials give way to complete elec- trical silence. 3. On attempted weak contraction, few motor units (the most excitable ones) are called into action and start to fire. The MUAPs are usually biphasic to triphasic in shape (2). The parameters of average normal MUAPs are 0.5-2 mV for amplitude and 5-15 ms for duration (2). Polyphasic potentials are seen normally and represent -12% of the MUAPs (3) (Fig. 1). 4. On increasing the strength of the contraction, these initial motor units increase their frequency of firing and new motor units are called into action. This recruitment increases until the baseline of the 159