respiratory dysfunction in myotonic dystrophy type 1 (DM1).

DM1 is a multisystem disease that causes muscle weakness and myotonia, as well as cognitive, cardiac conduction, gastrointestinal, and respiratory abnormalities. It affects 1 in 8000, and respiratory complications are the most common cause of death. The natural history of respiratory decline in DM1 is poorly characterized with few identified predictors of respiratory dysfunction progression.

Electronic medical records from 110 adult patients diagnosed with DM1 and seen at the Ohio State University Wexner Medical Center between 2009 and 2019 were reviewed. Respiratory symptom and pulmonary function data were obtained from routine evaluation with respiratory therapists. 

At baseline, 70.9% had restrictive respiratory impairment. Greater CTG repeat size, higher MIRS rating, and longer disease duration were all correlated with lower baseline FVC (r= -0.4819, p= <0.000; r= -0.5098, p= <0.0001; r= -0.3528, p= 0.0027). Longer disease duration was associated with greater annual VC decline (r= -0.663, p= 0.013). Annual rates of change of EtCO2, FVC, VC, and number of respiratory symptoms were not significantly different when stratified by CTG repeat size, MIRS, age at symptom onset, change in PFT severity, or baseline PFT severity.

Our data confirmed a high prevalence of restrictive respiratory impairment and identified characteristics associated with respiratory dysfunction and decline in DM1 patients. Longer disease duration was associated with greater annual decline in VC, suggesting that with disease progression restrictive respiratory impairments progressed at a faster rate. However, annual rate of change of EtCO2, FVC, and number of respiratory symptoms were not significantly different when stratified by CTG repeat size, MIRS, or age at symptom onset suggesting that factors contributing to respiratory decline in DM1 are complex and multifactorial due to individual variability in clinical phenotype.