Electromyographic pattern in Duchenne and Becker muscular dystrophy. Part I: Electromyographic pattern in subsequent stages of muscle lesion in Duchenne muscular dystrophy.

Background: The study was aimed to evaluate the EMG pattern in myopathy, in the muscles with early, slight abnormalities and in the muscles severely affected, and to analyze the sequence of abnormalities appearing with the progress of the impairment.

Material And Method: Fifty one boys with Duchenne muscular dystrophy were studied. Ninety nine proximal muscles (biceps brachii and rectus femoris) were examined. According to clinical criteria (defective force, atrophy) the muscles were assigned to the group of slight changes (group AB: 50 muscles) and to the group of severe abnormalities (group CD: 49 muscles). An own method of Functional-QEMG was applied in the CNEMG examination.

Results And Conclusions: The sensitivity of the method applied allowed the detection of myogenic changes even at the subclinical, oligosymptomatic (group AB) stage of impairment. The earliest EMG abnormality detected was an increased percentage of the polyphasic potentials, even if other MUAPs parameters remained normal. However at this stage already a decrease appeared of amplitude, area and MUAPs duration, along with the decrease of IP amplitude and amplitude size. An increase of IP density and a slight increase of number of stable-shaped potentials (simple, but more often polyphasic) was also seen which we believed to reflect the compensatory process. At the further stage, when compensating mechanisms were no longer possible, a dramatic decrease appeared of the IP amplitude, amplitude size and density and, sometimes, also a decrease in the number of stable-shaped potentials. The structural changes such as decrease of amplitude, area and MUAPs duration also progressed. These findings reflect in our study the sequence of EMG abnormalities in the successive stages of myogenic lesion.