Study data published in Sleep Medicine support the existence of distinct subtypes of hypersomnolence disorder distinguished by the presence or absence of psychiatric illness. The findings offer a potential nosological solution for a diagnosis plagued by heterogeneity.

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.

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Self-report total sleep time, Epworth Sleepiness Scale score, and Sleep Inertia Questionnaire score were captured at baseline. These variables were used in Ward D hierarchic clustering analyses to develop distinct symptom clusters, which were assessed for differences in patient characteristics.  

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In total, 62 individuals (mean age, 31.2±10.2 years; 90.3% women) were included in analyses. Nearly half (46.8%) of patients reported taking psychotropic medication.

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 (P =.001), difficulty with sleep inertia (P <.0001), hypersomnia severity (P =.0004), and functional impairment related to sleep (P =.0006), as well as worse depressive symptomatology (P <.0001). Patients in cluster A also reported worse overall sleep quality (P =.0002), and were more often taking psychotropic medications (P =.04) compared with those in cluster B.

In polysomnography tests, those in cluster A demonstrated longer time in bed (P =.006), total sleep time (P =.0002), N2 sleep time (P =.007), and rapid eye movement sleep time (P =.04), as well as better sleep efficiency (P =.003) and less time waking after sleep onset (P =.01). However, both clusters demonstrated similar multiple sleep latency test results.

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.

“Future research is necessary to solidify the conceptualization and characterization of unexplained hypersomnolence presenting with-and-without psychiatric illness,” the investigators wrote.

Disclosure: Two study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures


Cook JD, Rumble ME, Plante DT. Identifying subtypes of hypersomnolence disorder: a clustering analysis. Sleep Med. 2019;64:71-76.