Unravelling the sleepy brain: A neuroimaging study in central hypersomnolence disorders

Central disorders of hypersomnolence are mainly characterised by excessive daytime sleepiness despite normal timing of nocturnal sleep. All disorders greatly impair daily functioning. Three subtypes of central disorders of hypersomnolence are being distinguished: narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia. While narcolepsy type 1 originates from a selective loss of hypothalamic hypocretin-producing neurons, the pathophysiology underlying narcolepsy type 2 and idiopathic hypersomnia remains to be fully elucidated. It is probable that different causes may lead to these phenotypes.

The underlying brain circuit abnormalities of only narcolepsy type 1 have so far been identified using small sample groups, but their correspondence with other hypersomnolence disorders has yet to be investigated. As distinctive features between narcolepsy type 2 and idiopathic hypersomnia have not clearly been defined and given the clinical similarities between narcolepsy type 2 and idiopathic hypersomnia, the question arises whether the current third edition of the International Classification of Sleep Disorders (ICSD-3) classification addresses two separate entities or arbitrarily splits a heterogeneous group of patients. This is further emphasised by > 50% diagnosis crossover of NT2 and IH after repetition of diagnostic testing. In the future, the neural signatures of different central disorders of hypersomnolence could reveal transdiagnostic disease dimensions and help to improve classification of central disorders of hypersomnolence and potentially treatment options.

We expect brain structure and functioning to be different in the hypothalamus, thalamus, brainstem, amygdala, medial prefrontal cortex, cingulate cortex, pre- and postcentral cortex, basal ganglia and visual cortex in patients as compared to controls. We also hypothesize narcolepsy type 2 and idiopathic hypersomnia to show similar brain structure and activation.

Study will start with one week of actigraphy and a sleep diary. After this week MRI acquisition will be performed. Healthy controls will undergo the protocol twice, once well-rested and once with a night of partial sleep deprivation in the night before MRI acquisition.

NA