We studied data on seizures, vacant spells and breathing dysrhythmia from the British Rett Survey and 150 electroencephalographic records from 78 classic cases, including 23 with prolonged synchronous recordings of EEG, respiration and movement. In young girls the EEG abnormality increased in sleep but decreased during episodic hyperventilation and breath-holding. Epileptogenic activity was commonly present without clinical seizures. Eleven vacant spells were monitored and were not epileptic but related to the breathing abnormality.
Full monitoring is essential when supposed seizures are intractable.
The intermittent EEG abnormality and behavioural changes indicate abnormal fluctuating arousal possibly of midbrain or brainstem origin.