Avaliação não invasiva da taxa máxima de relaxamento dos músculos inspiratórios na distrofia miotônica

Abstract

INTRODUCTION: Myotonic dystrophy (DM) is a neuromuscular disease characterized by unstable expansion of CTG triplet on chromosome 19. It has two forms: type 1 (DM1 or Steinert's disease); and type 2 (DM2), being the former the most frequent and showing systemic manifestations, such as myotonia (muscle relaxation difficulty), cataracts, arrhythmias, muscle weakness and atrophy, among others, respiratory failure being one of the main factors predictive of mortality and a leading cause of death. OBJECTIVES: To evaluate the sensitivity / specificity of the maximum relaxation rate of the inspiratory muscles (MRR), the surface electromyography (sEMG) of the sternocleidomastoid (SCM), scalene (SCA), parasternal (2ICS), rectus abdominis (RA) and lung function/respiratory muscle strength in patients with DM1 and healthy subjects. METHODS: We invited 74 subjects to participate in the study, 44 patients with DM1 and 30 controls. The study included 31 subjects (18 DM1 and 13 controls). After exclusions, the final sample was of 27 subjects, 16 patients with DM1 and 11 healthy subjects. All of them were assessed for MRR of inspiratory muscles, for sEMG of the respiratory muscles, muscle and lung function. RESULTS: 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 of 0.87 (95% CI, 0.74 to 1.01, p=0.001). DM1 group showed lower PImax (p=0.0006), PEmax (p=0.0002), SNIP (p=0.0014), CVF%pred (p=0.0018) and FEV1%pred. (p=0.0004) and higher sEMG activity of the SCM (p=0.0022) and ESC muscles (p=0.004) at rest; of 2EIC (p=0.003) during PEmax and of SCM (p=0.02) and ESC muscles (p= 0.03) during the sniff test. CONCLUSIONS: The MRR is sensitive and specific to identify delayed relaxation of the respiratory muscles and respiratory muscle function is altered in patients with DM1.