Disability and survival in Duchenne muscular dystrophy

Background: Duchenne muscular dystrophy (DMD) leads to progressive impairment of muscle function, respiratory failure and premature death. Longitudinal data on the course of physical disability and respiratory function are sparse. Objectives: To assess prospectively physical impairment and disability, respiratory function and survival in patients with DMD over several years to describe the course of the disease with current care. Methods: In 43 patients with DMD, aged 5-35 years, yearly assessments of physical disability by the Duchenne muscular dystrophy physical Impairment and Dependence on care (DID) score, ranging from 9 (no disability) to 80 (complete dependence), and forced vital capacity (FVC), were obtained over a mean time interval of 5.4 (SD 2.1) years. Results: DID scores were correlated with age according to a hyperbolic function (f = 85.36age/(10.05+age), R = 0.62, p<0.0001). FVC declined exponentially with age (f = 139.1xexp(-0.08xage), R = 0.52, p<0.0001). Mean age at which patients lost their ambulation was 9.4 (SD 2.4) years and they became dependent on an electric wheelchair at 14.6 (4.0) years. Age at the beginning of assisted ventilation was 19.8 (3.9) years, Three patients died during the observation period. The estimated probability of survival to age 30 years was 85% (median survival was 35 years). Conclusions: Our detailed observations of the progression of physical disability, dependence on care and respiratory impairment in patients with DMD from childhood to adult life is valuable for predicting the clinical course with current medical care. Compared with historical data, survival has improved considerably.