Isolated diaphragmatic tremor: is there a spectrum in "respiratory myoclonus"?

BACKGROUND

Respiratory myoclonus or diaphragmatic flutter is an unusual movement disorder with abnormal diaphragmatic activity, which may be associated with respiratory symptoms. The effects of distracting maneuvers on diaphragmatic activity have not been investigated.

METHODS

Two patients with nondisabling abdominal movements of suspected diaphragmatic origin were studied with surface and needle electromyography (EMG).

RESULTS

The abdominal movements resulted from isolated, rhythmic diaphragmatic contractions with variable EMG burst duration, suppressibility with breath-holding and distracting maneuvers, and other attributes of volitional control.

CONCLUSION

"Respiratory myoclonus" may be a heterogeneous disorder ranging from synchronous movements of the diaphragm and other respiratory muscles associated with respiratory compromise, to diaphragmatic movements under at least some volitional control with no respiratory or functional disability. The latter group could be designated phenomenologically as "isolated diaphragmatic tremor."