Abstracts

Rationale: Trigger mechanisms of psychogenic non-epileptic seizures (PNES) are presumed to be multiple, as the range of neurobehavioral manifestations. The medical setting seems important, but debates over the clinical protocol of PNES induction have not addressed specific contributing factors. A retrospective study examined whether conversion of EEG recording from analog to digital altered the laboratory incidence of clinical non-epileptic events. Methods: A standard EEG of 20-30 minutes’ duration included hyperventilation and intermittent photic stimulation, unless contraindicated. The electroencephalograph was placed next to the patient without video monitoring. The laboratory procedures have not changed except that the electroencephalograph was converted from analog polygraphic to digital, beginning in 1995 and completing in 1999. The recording EEG technologist was to recognize clinical events, to notate clinical characteristics, and to confirm correspondence to the clinical history, when available. The requesting physician at times indicated clinical suspicion, but no specific protocol was applied to induce a clinical event. Results: A total of 12788 standard EEG records were reviewed by a single clinical electroencephalographer over a 19-year period (1990-2008). Clinical non-epileptic events were captured in 212 records (1.66%), declining from 1.87% for 5 analog years (1990-1994) to 1.16% for 9 digital years (2000-2008: p<0.05), separated by 5 transition years. Chloral hydrate was given to 3 patients in 1990 and 1991. Some patients met the physician but only after the clinical event. The majority of events were unrelated to EEG activation procedures. Conclusions: The moving paper and pens of analog EEG recording generate noises that are absent in digital recording. The recording paper is folded and adds low frequency periodic components, while the pen noise sensitively reflects the patient’s own movement. Suggestions of relaxation, drowsiness-sleep, hyperventilation, and photic stimulation have been incorporated in both EEG recording and hypnotic induction procedures. The literature of hypnosis and absorption-dissociation emphasizes factors affecting suggestibility, but the debate over PNES induction protocols has mostly concerned so-called secondary suggestibility. The investigation was preliminary and limited in scope, because clinical event characteristics were not scrutinized, but indicates that investigations of PNES can benefit from a broader neuropsychophysiological orientation.