Different mechanism may underlie respiratory failure of myotonic and Duchenne muscular dystrophies--a pulseoxymetric and spirometric study

Respiratory failure is an important cause of death in many neuromuscular diseases. We studied the relationship between nocturnal hypoxemia and respiratory muscle weakness by nocturnal pulseoxymetry and spirometry in two major hereditary myopathies, myotonic and Duchenne muscular dystrophies (MD and DMD respectively). In DMD significant nocturnal periodic hypoxemia appears only in cases with vital capacity lower than 20% of its expected value, suggesting that % vital capacity is a useful index of early respiratory failure. In contrast there was no correlation between vital capacity and severity of hypoxemia in MD patients. Therefore, we conclude respiratory muscle weakness is a single important factor which determines the severity of respiratory failure in DMD, while another/other factor (s), such as disturbance of respiratory control or myotonia, may play an important role in MD.