Noninvasive assessment of respiratory muscle strenght and activity in myotonic dystrophy

Abstract

We hypothesized that markers of myothonia can be found in patients with Myothonic Dystrophy by analyzing different parameters describing the strength, the relaxation and the electrical activity of respiratory muscle. We have considered MIP, MEP and SNIP as indexes of strength and MRR and sEMG as indexes of muscle relaxation and contraction.We invited 74 subjects to participate in the study, 44 patients with DM₁ and 30 controls. The study included 31 subjects, after exclusions, the final sample was 27 subjects (16 DM₁ group/11 control group(. The MRR of inspiratory muscles and sEMG of the respiratory muscles were assessed.The MRR was lower in patients with DM₁ vs. control (p = 0.001) and was considered sensitive and specific to identify the disease in DM₁ and discard it in the control group, ROC area was 0.87 (95% CI, 0.74 to 1.01, p=0.001). The contraction time of SCM/ESC were higher in DM₁ group vs.control respectively during PImax (p=0.023,p=0.017) and SNIP (p=0.015 and p=0.0004). The DM₁ group showed lower respiratory muscle strength PImax (p=0.0006), PEmax (p=0.0002), SNIP (p=0.001), and higher sEMG activity of the SCM (p=0.002) and ESC muscles (p=0.004) at rest; of 2^ndIS (p=0.003) during PEmax and of SCM (p=0.02) and ESC muscles (p=0.03) during the sniff test. The SNIP%, PImax% and PEmax% were considered sensitive and specific to identify the disease in DM₁ and discard it in the control group.Our results provide information that can contribute to a better understanding of myotonic dystrophy and its impact on the respiratory system (either in its functional or muscular aspect) and thus help in the development and use of evaluation methods that may be routinely used in clinical practice.