A 52-year-old woman with severe restrictive lung disease and dilated cardiomyopathy secondary to nemaline myopathy1 was referred to the Sleep Unit for night choking and snoring. She presented dyspnea on minimal exertion and in the supine position. A conventional polysomnography (PSG-C) with percutaneous capnography was performed.
The study showed moderate obstructive sleep apnoea, premature ventricular contractions and an increase in PtCO2 from 39 to 51mmHg. We observed cyclic activations in the chin electromyogram (EMG) and a simultaneous artifact in the electroencephalogram (EEG) and electrooculogram (EOG) derivations (Fig. 1).
The cyclic muscle activity in the EMG/EEG/EOG channels corresponds to the contraction of the sternocleiodmastoid muscle in a patient with severe restrictive lung disease who needs to use accessory respiratory muscles. The sternocleidomastoid muscle has an insertion in the mastoid process, thus near the location of the referential electrode (M1) in a PSG-C.2 Its excessive activation in this patient is the reason why the contraction becomes visible in the EEG and EOG derivations that were also referred to the same electrode.
Conflict of interestThe authors declare to have no conflict of interest.
