8 - NEEDLE ELECTROMYOGRAPHIC ABNORMALITIES IN NEUROGENIC AND MUSCLE DISEASES

Abstract

This chapter discusses general pattern of changes in motor unit potentials (MUPs) as recorded with a standard concentric needle electrode in primary muscle and neurogenic diseases in comparison to normal single muscle fiber and MUPs. It presents coherent techniques in combination with amplitude discrimination to help the operator to visualize and select MUPs and discusses automatic or semi-automatic devices to measure the numbers of phases (baseline crossings), durations, and amplitudes of these MUPs. The chapter also describes the means to analyze the significance of any apparent departures from normal values established for the particular type of electrode and recording technique employed, muscle selected, and age of the subject. In most instances of primary diseases of muscle, there is an increase in the proportion of shorter duration motor unit action potentials, many of which are composed of multiple spike components and more than four phases. In other instances, the duration and shape of the motor unit action potentials suggest that the potential may be generated by a single muscle fiber only within the pickup territory of the recording electrode. Other muscle fibers belonging to the same motor unit are possibly distant or too weak a voltage source to be detected. Despite the shorter mean duration of the main motor unit action potential complex, many such potentials are linked to other action potentials that precede or follow the main potential by an appreciable interval.