Electromechanical delay components during skeletal muscle contraction and relaxation in patients with myotonic dystrophy type 1

Aim: The electromechanical delays during muscle contraction (DelayTOT) and relaxation (R-DelayTOT) can be partitioned into mainly electrochemical and mechanical components by an electromyographic (EMG), mechanomyographic (MMG), and force (F) combined approach. Their assessment could provide new insights on the alterations that characterize skeletal muscle dysfunction in patients with myotonic dystrophy type 1 (DM1). Methods: DelayTOT and R-DelayTOT components duration and reliability were investigated during muscle contraction and relaxation in thirteen DM1 (age: 38 ± 15 yrs; body mass: 75 ± 14 kg; stature: 1.78 ± 0.07 m; mean ± SD) and in thirteen age- and bodymatched healthy controls (HC) from tibialis anterior and vastus lateralis muscles during maximum voluntary and electrically-evoked isometric contractions. Possible correlations between DelayTOT and R-DelayTOT components and scores for clinical evaluation in DM1 patients (MRC, MIRS and Rivermead score) and their genetic characterization (number of CTG expansion) were also determined. Results: Force was lower in DM1 than in HC under both experimental conditions. DelayTOT and R-DelayTOT components were significantly longer in DM1 in both muscles, with a similar impairment of the electrochemical and mechanical components. Measurements reliability was very high (ICC from 0.82 to 0.97). DelayTOT and R-DelayTOT correlated with MRC, MIRS, Rivermead scores and CTG expansion (R2 from 0.439 to 0.975). Conclusions: The differences between DM1 and HC in DelayTOT and R-DelayTOT components, the high reliability and the strong correlations with the clinical scores and CTG expansions suggest that the EMG, MMG and F combined approach may represent a valid tool to assess the level of neuromuscular dysfunction. (118 EP P)