To split or to lump? Classifying the central disorders of hypersomnolence

Abstract

The classification of the central disorders of hypersomnolence has undergone multiple iterations in an attempt to capture biologically meaningful disease entities in the absence of known pathophysiology. Accumulating data suggests that further refinements may be necessary. At the 7th International Symposium on Narcolepsy, a group of clinician-scientists evaluated data in support of keeping or changing classifications, and as a result suggest several changes. First, idiopathic hypersomnia with long sleep durations appears to be an identifiable and meaningful disease subtype. Second, idiopathic hypersomnia without long sleep time and narcolepsy without cataplexy share substantial phenotypic overlap and cannot reliably be distinguished with current testing, and so combining them into a single disease entity seems warranted at present. Moving forward, it is critical to phenotype patients across a wide variety of clinical and biological features, to aid in future refinements of disease classification.

Keywords: classification; hypersomnolence; idiopathic hypersomnia; narcolepsy.

Figure 1.

Protocols for measuring sleep time in idiopathic hypersomnia. Several protocols are currently in use for measurement of sleep time in people with idiopathic hypersomnia. Gray bars indicate periods where participants are asked or allowed to sleep, with the size of the bars indicating relative duration (see text for details).

Figure 2.

Current International Classification of Sleep Disorders, third edition, versus proposed grouping. The ICSD-3 lists eight central disorders of hypersomnolence, including narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia (top row). Based on current data, the authors propose combining those with narcolepsy type 2 and those with idiopathic hypersomnia without long sleep time into a single, new diagnosis called “Narcolepsy spectrum disorder” (bottom row).