THE RESPIRATORY MUSCLES IN MULTICORE MYOPATHY

Multicore myopathy is a rare congenital myopathy that can cause progre ssive weakness, but it has not been recognized previously to have resp iratory consequences. This study describes two patients who developed respiratory failure because of respiratory muscle weakness. Both patie nts had low vital capacities without evidence of airway obstruction, a nd CO2 retention. Physical examination found that neck accessory muscl es and abdominal muscles were very weak. In inspiration the abdomen ex panded, but the rib cage contracted. Detailed studies were done in one patient with magnetometers, esophageal and gastric pressures, flow an d volume, and electromyograms of abdominal and neck accessory muscles. Peak static inspiratory and expiratory pressures were 28 and 30 cm H2 O, respectively, and maximal transdiaphragmatic pressure was 28 cm H2O . Vital capacity was reduced to 44% of predicted. Lung compliance was normal. In spontaneous breathing while supine, rib-cage diameters decr eased while gastric pressure increased in inspiration, suggesting the weak diaphragm was the main muscle of respiration. EMG recordings show ed no evidence of recruitment of the wasted neck accessory muscles (st ernocleidomastoid and scalene), whereas electromyograph plus mechanics measurements gave evidence of abdominal muscle use in the sitting but not the supine posture. More limited studies in the second patient ga ve similar results. Multicore disease in these two patients thus cause d marked weakness of all respiratory muscles, affected the intercostal -accessory group more than the diaphragm, and led to respiratory failu re.