[Serial observations of respiratory function in disabled patients with myotonic dystrophy]

Serial assessments of respiratory function were performed over 1 to 8 years in 12 patients with myotonic dystrophy. Respiratory parameters included vital capacity (percentage of predicted value; %VC) and one-second forced expiratory volume (percentage of predicted value; FEV1.0%) on spirogram and arterial blood gases at rest. The patients who had no primary respiratory disease were ranged in age from 31 to 61 years, with an average age of 47 years, and their mean duration of illness was 20 years. All the subjects were severely disabled; only two patients were able to walk with assistance, but other ten patients were confined to a wheelchair. During the observation period, five patients died; 4 due to respiratory failure and one cardiac and respiratory failure. The following results were obtained: (1) almost all the patients showed a reduction in %VC, the severity of which was gradually progressed with advancing age. A significant negative correlation was observed between %VC and duration of illness. (2) PaCO2 was negatively correlated with %VC, while the relationship between PaO2 and %VC appeared to be a significant positive correlation. Chronic alveolar hypoventilation (hypercapnia and hypoxemia) was particularly likely when vital capacity (VC) was less than 40% of the predicted value in the patients. This study indicates that a reduction of VC plays an important role in development of respiratory failure in myotonic dystrophy and serial measurements of VC and arterial blood gases are useful in the detection of it.