Co-activation of rhythms during alpha band oscillations as an interictal biomarker of exploding head syndrome.

BACKGROUND: Exploding head syndrome is a rarely reported benign sensory parasomnia that may nonetheless have significant impact on patients' quality of life and their perceived well-being. To date, the mechanisms underlying attacks, characterised by a painless perception of abrupt, loud noises at transitional sleep-wake or wake-sleep states, are by and large unclear. METHODS AND RESULTS: In order to address the current gap in the knowledge of potential underlying pathophysiology, a retrospective case-control study of polysomnographic recordings of patients presenting to a tertiary sleep disorders clinic with exploding head syndrome was conducted. Interictal (non-attack associated) electroencephalographic biomarkers were investigated by performing macrostructural and event-related dynamic spectral analyses of the whole-night EEG. In patients with exploding head syndrome, additional oscillatory activity was recorded during wakefulness and at sleep/wake periods. This activity differed in its frequency, topography and source from the alpha rhythm that it accompanied. CONCLUSION: Based on these preliminary findings, we hypothesise that at times of sleep-wake transition in patients with exploding head syndrome, aberrant attentional processing may lead to amplification and modulation of external sensory stimuli.

Posttraumatic narcolepsy--two case reports and a mini review.

STUDY OBJECTIVES: Hypersomnia following head injury is quite common, but the diagnosis of posttraumatic narcolepsy has tended to court controversy to the extent that the existence of this disorder has been questioned. The recent discovery of the hypocretins (orexins) and the subsequent confirmation that their deficiency causes narcolepsy have shed light on the pathophysiology of narcolepsy. Damage to or dysfunction of the hypothalamic cells that produce hypocretin (orexin), from whatever cause, can give rise to narcolepsy. We have conducted a review of the literature on the subject and have included only those cases that have been confirmed by polysomnography. There are approximately 20 polysomnography-confirmed cases of posttraumatic narcolepsy published in the literature, to which we add a further 2 cases. The results suggest that patients with posttraumatic narcolepsy are a heterogeneous group with respect to clinical presentation, nature and severity of injury, time from index event to symptom onset, and HLA type. There is some evidence that this type of narcolepsy may follow a progressive course, suggesting that the index event sets off a cascade sequence that may involve the hypocretin system. Further research in this area is required to answer these hypotheses.