Discriminating neurological from psychiatric hypersomnia using the forced awakening test.

INTRODUCTION: Sleep inertia refers to the inability to attain full alertness following awakening from sleep and is a major component of hypersomnia. As event-related potentials (ERPs) are correlated to the degree of consciousness, they allow exploring information processing in transitional states of vigilance. Their modifications during forced awakening (FA) context have been shown to reflect sleep inertia. OBJECTIVES: To assess the diagnostic value of a FA test using an oddball stimulation protocol during a nap in a representative sample of patients with excessive daytime sleepiness (EDS). METHODS: One hundred and seventy three patients [30 narcolepsy, 62 idiopathic hypersomnia, 33 sleep apnoea syndrome, and 48 other (mainly psychiatric) hypersomnia] performed an auditory target detection stimulation task during pre-, post-nap wakefulness, and during two successive intra-nap FA while the EEG was simultaneously recorded. Both the accuracy of target detection and the ERPs were evaluated. ERPs during forced awakening test were considered to reflect sleep inertia if they presented with a P300 delay and/or sleep negativities (N350/N550). RESULTS: Pre-nap behavior and ERPs were normal in all patients. Behavioral results were significantly worse during FA than during wakefulness for all groups of patients. P300 latencies were significantly delayed on FA conditions in each group of patients except the psychiatric group. Sensitivity and specificity for detection of sleep inertia were 64% and 94%, respectively, with predictive values of 96% (positive) and 50% (negative). CONCLUSIONS: Our results suggest that the FA test could be helpful as a diagnostic procedure for discriminating neurological from psychiatric hypersomnia.