Changes of cortico-spinal excitability in obstructive sleep apnea

Motor cortical excitability is depressed during non-REM sleep in normal subjects. We have used single pulse transcranial magnetic stimulation in 5 patients with obstructive sleep apnoea syndrome (OSAS), to assess the relaxed threshold, silent period and the modification in amplitude of a test stimulus in wake, non-REM sleep and non-REM sleep during apnoea. Threshold was normal (52.6% +/- 3.6), the lasting of the silent period was increased (252 +/- 16 msec). During non-REM sleep the amplitude of the test motor evoked potential was reduced (52% of control; +/- 7.2) if compared with an awake condition, we observed a further decreased in amplitude (14% of control; +/- 6.5) when the same stimulus was given within apnoea. This transient modification of the cortical excitability may somehow relate to the intrinsic mechanisms of the OSAS pathophysiology.