Power spectrum analysis and conventional electromyogram in Duchenne muscular dystrophy

A comparative study of automatic electromyogram analysis (power spectral analysis) and manual measurements of the individual motor units potentials parameters in normal and Duchenne muscular dystrophy patients was performed to assess the diagnostic yield of both methods.

The analysis of 20 motor unit potentials elicited at weak effort manually by visual assessment and by power spectrum analysis at 1400 Hz Haning window were performed with concentric needle electrode in the biceps brachii and tibialis anterior. The study includes 18 healthy controls and 32 Duchenne muscular dystrophy patients. The primary diagnosis of the patients was based on the clinical criteria, family history and serum creatin kinase activity estimation. Seventeen patients were biopsied for further histological and histochemical examination.

The conventional electromyogram of the patient group characterized by condensed, low mean amplitude of the recruited pattern and an increase in the percentage of polyphasic potentials of short duration and low amplitude in comparison to the normal subjects. About 74% of the patients were identified as myopathic patients with this method. Power spectrum analysis showed significant increase (P<0.0005) in the mean power frequently and the relative power at 1400 Hz and a significant decrease (P<0.0005) in accumulated power. About 95% of the patients were identified as being myopathic patients by this method. Statistical correlation analysis revealed no relationship between the power spectrum analysis and motor unit potentials parameters.

The electromyogram power spectra was shifted to the higher frequencies in the Duchenne muscular dystrophy patients as compared to the control. The diagnostic yield of the electromyogram power spectrum analysis was higher than the measurement of the motor unit potential parameters. The best parameter of the electromyogram power spectrum is the relative power at 1400 Hz than the other two parameters. The net result of this study is that the electromyogram power spectrum has diagnostic possibilities in the muscles, which showed normal, or few motor unit potential changes.