Respiratory myoclonus. Report of a case with electromyographic study

A case of respiratory myoclonus in a 45 year-old male was studied by electromyography. He complained of anorexia, involuntary swinging movement of the thorax and trunk, and epigastric pulsation. Electromyographic studies showed synchronous rhythmic grouped discharges at the of 2 to 3 Hz from the bilateral 8th to 10th intercostal muscles, the right iliocostalis lumborum muscle, and the left hemidiaphragm only during the expiratory phase. They disappeared on inspiration and forced expiration. Anesthetic block of the left phrenic nerve abolished both the voluntary and myoclonic movements of the left hemidiaphragm. Abnormal excitation of the central nervous system and possible irritation of the afferent pathways were postulated.