Idiopathic Hypersomnia and Hypersomnolence Disorder: A Systematic Review of the Literature

Background: Hypersomnia is a common complaint in medical offices. Often patients are given psychiatric diagnoses, but a primary sleep disorder may be present. The new diagnosis of "hypersomnolence disorder" (HD) in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition is a primary sleep disorder most similar to the diagnosis "idiopathic hypersomnia" (IH) in sleep literature and can be missed in psychiatric settings.

Methods: A systematic review of the computerized databases PubMed, EMBASE, Web of Science, and Psychinfo using the search criteria "idiopathic AND (hypersomnolence OR hypersomnia)," as well as "hypersomnolence disorder was conducted." Articles were included if they were in English and included information regarding the epidemiology, diagnosis, pathophysiology, or treatment of IH or HD. Where relevant, weighted means and 95% CI were calculated based on the number of subjects in each study.

Results: A total of 143 articles discussed IH, whereas no articles were found regarding HD. Most articles were review articles, prospective studies, or studies of pathophysiology. IH is found in approximately 0.02%-0.010% of the general population, has a mean age of onset of 21.8 years, and is associated with several somatic symptoms. Alterations in histaminergic or dopaminergic signaling may be involved in IH. Treatment with modafinil or other stimulants appears moderately effective. IH can be differentiated from psychiatric hypersomnolence by formal polysomnography.

Conclusions: IH and HD are relatively uncommon disorders and little is known about them. However, they are distinct from psychiatric disorders and respond well to treatment once properly identified.