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Fatigue trends in and the diagnosis of myasthenia gravis by frequency analysis of EMG interference patterns
Author(s) -
Yaar Israel,
Mitz Andrew R.,
Pottala Erik W.
Publication year - 1985
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880080410
Subject(s) - myasthenia gravis , isometric exercise , electromyography , biceps , frequency analysis , medicine , muscular fatigue , cardiology , psychology , physical medicine and rehabilitation , mathematics , statistics
Twenty patients with myasthenia gravis were studied. Needle interference patterns at maximal isometric contractions were recorded from the biceps brachii muscles. Each recording lasted for 30 seconds and induced som fatigue. The EMG signals were transformed into power spectra and were analyzed for differences between control and myasthenic fatigue trends and were tested for the power of the frequency variables to classify unknown subjects. Both groups showed a similar averaged spectra for the first 5 seconds. Thereafter, the controls manifested continuous increase in power, and a power peak frequency shift toward low frequencies. The myasthenics showed an initial increase throughout the frequency ranges; however, later, there was a marked decrease in power and their peak frequency shifted toward the lower frequencies. These fatigue trends differed significantly from one another. Discriminant analysis correctly classified 83% of the subjects. This technique may be helpful in the diagnosis of myasthenia gravis.