Sarcolemmal excitability in myotonic dystrophy: assessment through surface EMG

A motor point stimulation protocol was carried out on the tibialis anterior of myotonic dystrophy (MyD) patients. The surface myoelectric signal was monitored to record average rectified value (ARV), median frequency of power spectrum (MDF), and conduction velocity (CV) parameters. The ARV curve showed a decreasing trend that reveals a reduction in the M-wave amplitude during stimulation. MDF presented a significant decrement in the first seconds of sustained contraction, probably caused by abnormal lengthening of the depolarization zone. CV was significantly lower in patients, suggesting reduced mean fiber size.