筋緊張性ジストロフィー症における睡眠時呼吸病態

Myotonic dystrophy is a gentic disorder inherited as an autosomal dominant trait. It is known to be associated with endocrine dysfunction, polar cataracts, cardiac abnormalities and other conditions. Respiratory distress constituts the principal problem in myotonic dystropy. The author investigated postural change of respiratory function in 12 patients with myotonic dystrophy (MYD), and 7 patients with limb-girdle dystrophy (LG) and overnight polysomnography was performed on 10 patients with MYD and 5 patients with LG.<br>The respiratory function in seated posture showed no significant difference between LG and MYD, but in patients with MYD, the vital capacity and the expiratory reserve volume in a supine posture was reduced in comparison to that during seated poture. However, the respiratory function in patients with LG was not significantly different in seated and supine postures.<br>Also, in patients with MYD, there was a significant decrease in arteiral PO₂ from the seated posture to the supine posture, without a significant change in the arterial PCO₂. However, in patients with LG, there was no significant change in arterial blood gas analysis parameters.<br>It was speculated that these findings concerning respiratory function and blood gas analysis in patients with MYD were caused by the involvement of the diaphragm. In the supine posture, the diaphragm shifted to the cranial position because of the abdominal contents rising into thorax, therefore the lung volume was reduced and the ventilation-perfusion ratio deteriorated. The changes of respiratory function parameters and PaO₂ were partly responsible for the hypoxemia observed during sleep in patients with MYD.<br>Overnight polysomnography showed that 9 of the 10 patients with MYD and 1 of the 5 patients with LG presented apneas during sleep, particularly during REM, stage 1 and stage 2. Almost all apneas were central type, with a low percentage of obstructive apneas and the apnea index was 19.0/h (mean) in MYD, 6.5/h in one case of LG. These result strongly suggest that sleep apnea is of central origin, but the distinction between a central and an obstructive etiology is dificult in neuromuscular disease and particularly when a disorder of central ventilatory responsiveness is suspected.<br>The respiratory function of MYD and LG in seated and supine postures was studied and overnight polysomnograpy performed. It was emphasized that it was important for the respiratory care of neuromuscular disease to consider the influence of postural changes in the respiratory function. The present series of studies revealed central sleep apnea in the patients with myotonic dystrophy. These findings explained susceptibility to respiratory failure in myotonic dystrophy.