Abstract
The most commonly used EMG method for daily routine is that obtained with concentric needle electrodes, and a number of parameters have been used to characterize the motor unit action potential (MUAP). It is important to understand the physiological meaning of each parameter and pathology of neuropathic and myopathic disease. Amplitude is measured as maximal peak to peak voltage. It determined by muscle fibers within 0.5mm from the electrode, i. e. a few fibers in normal subjects. Reduced amplitude means atrophy of muscle fibers, decreased numbers of the muscle fibers just near the electrode, excessive jitter and bocking. Incresed amplitude means focal grouping (reinnervation with sprouting, regeneration of split fibers), hypertrophy of muscle fibers. Duraion is the time between the starting-point and end-point of the slow component of the MUAP and related to number of muscle fibers within radius of 5mm. Reduced duration means loss of muscle fibers and increased duration indicates increased number of muscle fibers, e. g. collateral sprouting. Increased number of phases means increased slow conduction in terminal axons, and/or increased variability of muscle fiber diameter. Pathological changes in acute denervation are the appearance of non-functional motor unit, muscle fiber atrophy, and slow conduction in terminal axon branch; then polyphasic but not high amplitude and long duration MUAPs are detected. In chronic denervation, grouping and increased numbers of muscle fibers was occurred by reinnervation with sprouting are appeared; then high amplitude and long duration MUAPs are detected. In myopathy, atrophy and/or loss of muscle fibers and variation of muscle fiber diameters (compensatory hypertrophy) are the main pathological changes; then MUAPs in myopathy are low ampulitude (high amplitude MUAPs are also detected near the hypertrophic muscle fibers), short duration, and polyphasic. Evaluation of interference pattern is also very important. Loss of motor units is the main pathologial change in neuropathy even in the acute and chronic neurologenic changes. Early recruitment or pathological interference is chracteristic in myopathy. Evaluation of interference pattern is also very important. Loss of motor units is the main pathological change in neuropathy even in the acute and chronic neurologenic changes. Early recruitment or pathological interference is chracteristic in myopathy.
