Predictors of respiratory failure and survival in myotonic dystrophy type 1

IntroductionMyotonic dystrophy type 1 (DM1) is characterized by a lifelong progressive muscular weakness associated with life-threatening events such as chronic respiratory failure (CRF). Early identification of patients at risk remains challenging.ObjectiveTo identify clinical and biological markers predictive of CRF onset and survival in a large DM1 cohort.MethodsWe conducted a retrospective cohort study of 126 DM1 adult patients followed from 2000 to 2024 at Rouen University Hospital. The primary outcome was the first forced vital capacity (FVC) ≤ 70% of predicted value. Prognostic factors were analyzed using Cox proportional hazards models with the start of follow-up at the time of diagnosis of DM1 and were followed until the outcome occurred, or death (censorship according to Kalbfleisch & Prentice approach to competing risks).ResultsDuring a median follow-up of 12.5 years, 45 patients developed FVC ≤ 70%. Muscular impairment rating scale (MIRS) (HR: 1.85, 95%CI:1.30-2.63) and conduction/rhythm disorders (HR: 3.13, 95%CI: 1.37-7.31) at diagnosis were independent predictors of FVC ≤ 70% adjusted on age, female sex (HR: 1.54, 95%CI: 0.82-2.91) and cataract at diagnosis (HR: 0.50, 95%CI: 0.22-1.16). CTG repeats ≥400 was associated with a doubled risk of respiratory decline but did not reach statistical significance. The 20-year mortality rate was 32%. MIRS (HR: 2.34, 95%CI:1.22- 4.51), male sex and older age at diagnosis significantly predicted death.ConclusionsMuscular impairment and cardiac rhythm/conduction disorders at diagnosis were strong predictors of respiratory complications. MIRS, male sex and older age at diagnosis were predictors of mortality in DM1. These prognostic markers should inform clinical management strategies to improve survival in DM1 patients.