Study data published in Sleep Medicine support the existence of distinct subtypes of hypersomnolence disorder distinguished by the presence or absence of psychiatric illness.

Jessica Cook, PhD, Meredith E. Rumble, PhD, and David Plant, MD, PhD, conducted the study at the sleep laboratory and clinic of the University of Wisconsin-Madison. Patients undergoing polysomnography and multiple sleep latency test at the clinic were recruited, and those with hypersomnolence without an explanatory diagnosis were eligible for inclusion.

Clustering analyses produced 2 clusters of patients: (1) cluster A (n=32) and cluster B (n=30). Compared with cluster B, patients in cluster A described greater subjective daytime sleepiness (=.001), difficulty with sleep inertia (<.0001 hypersomnia severity>P =.0004), and functional impairment related to sleep (=.0006), as well as worse depressive symptomatology (<.0001 patients in cluster a also reported worse overall sleep quality>P =.0002), and were more often taking psychotropic medications (=.04) compared with those in cluster B.

The small sample size limited the strength of these conclusions, and the uneven gender distribution of participants may also affect data generalizability. Nonetheless, these results demonstrate the existence of 2 potential subclassifications of hypersomnolence disorder distinguished by the presence and severity of psychiatric symptoms as well as by sleep characteristics.