Electrically-elicited surface mechanomyogram in myotonic dystrophy

The surface oscillation of the muscle during electrical stimulation is detectable by an accelerometer as a surface mechanomyogram (MMG). The aim of this study was to evaluate whether MMG properties reflect the mechanical muscle changes induced by myotonic dystrophy (MyD). To this end, the tibialis anterior of seven MyD patients and seven age- and sex-matched controls (C) was supramaximally stimulated at 1 (single twitches), 5, 10, 15, 20 Hz for 3 s at the most proximal motor point.ResultsSingle twitches: The MMG amplitude was 67% less, the duration 37% longer, the electromechanical delay 64% longer, and the spectrum mean frequency 44% lower in the MyD patients than in controls.Repetitive stimulation At each stimulation frequency, the average MMG peak-to-peak was less in the MyD patients than in C.Conclusion The differences between the MMGs of MyD patients and C support the hypothesis that, together with the well-known changes in sarcolemmal excitability, an alteration in electromechanical coupling and a failure in contractile machinery may coexist in MyD.SommarioL'oscillazione presente alla superficie di un muscolo durante stimolazione elettrica può essere rilevata grazie ad un accelerometro come meccanomiogramma di superficie (MMG). Questo studio ha lo scopo di valutare se le caratteristiche del MMG riflettono i cambiamenti indotti dalla distrofia miotonica (DM) nella meccanica muscolare. Per questo motivo il tibiale anteriore di 7 pazienti DM e di 7 soggetti di controllo (C) è stato stimolato con ampiezza sopramassimale al punto motore più prossimale per 3 s a 1 (scossa singola), 5, 10, 15 e 20 Hz.RisultatiScossa singola IN DM, rispetto ai controlli, l'MMG ha presentato: ampiezza 67% inferiore, durata 37% superiore, ritardo elettromeccanico 64% superiore, frequenza media dello spettro 44% più bassa.Stimolazioni ripetute Ad ogni frequenza l'ampiezza del MMG è risultata inferiore in DM rispetto ai C.Conclusione I nostri risultati supportano l'ipotesi che nella DM, insieme alle già note alterazioni dell'eccitabilità sarcolemmale, può coesistere una alterazione dell'accoppiamento elettromeccanico ed una insufficienza dell'apparato contrattile della fibra muscolare. Quanto sopra à riflesso nelle differenze tra oscillazione meccanica di superficie dei soggetti DM e C.

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