Updated: Jul 24, 2019
The terms "with long sleep" and "without long sleep" never did adequately describe the two forms of Idiopathic Hypersomnia. However did the ICSD3 (International Classification of Sleep Disorders, third edition) get it right by simply combining the two into one? Not according to the thorough cluster analysis produced by Karel Šonka, Marek Šusta and Michel Billiard, Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis. This analysis supports the findings of previous studies that suggest Polysymptomatic Hypersomnia/complete Idiopathic Hypersomnia (previously referred to as with long sleep) is, in fact, distinct and unique and is, therefore, an independent sleep disorder of Monosymptomatic Hypersomnia/incomplete Idiopathic Hypersomnia (previously referred to as without long sleep). The research also showed, which has been the long-held belief of many researchers, that the clinical features of Monosymptomatic Hypersomnia are more closely related to those found in Narcolepsy without cataplexy (Type 2 Narcolepsy) and that those two disorders should be merged into one single condition.
Highlights from the study:
Hierarchical cluster analysis reviewed the classification of central hypersomnias.
Narcolepsy with cataplexy and idiopathic hypersomnia with long sleep time constituted independent clusters.
Narcolepsy without cataplexy and idiopathic hypersomnia without long sleep time entered into the same cluster.
Narcolepsy without cataplexy and idiopathic hypersomnia without long sleep time should merge into a single condition.
In an interview with Neurologia, Karel Šonka said that the ICSD3 new combined Idiopathic Hypersomnia "seems to be defined negatively against narcolepsy and secondary and comorbid hypersomnias and encompasses perhaps a variety of different diseases." He explained that it was "this step back in the definition of idiopathic hypersomnia" that led him and Billiard to perform the cluster analysis that determined Polysymptomatic Hypersomnia/complete Idiopathic Hypersomnia is not the same disorder as Monosymptomatic Hypersomnia/incomplete Idiopathic Hypersomnia. This analysis correlates very well with previous studies as well as the differences that we see in people's symptoms. While there is still some work to go in defining these disorders the three clusters in this study better represent the different forms of Narcolepsy and Idiopathic Hypersomnia than those that have been included in the ICSD3.
It should be noted that it is acknowledged in the analysis that the terms “with long sleep time” and “without long sleep time” are inappropriate as patients with both disorders can experience long sleep. There are other symptoms that have been determined that distinctly separate Polysymptomatic (complete) & Monosymptomatic (incomplete) Idiopathic Hypersomnia. These names, therefore, do not simply replace "with and without long sleep". The analysis needs to be read in full to get a complete understanding of how Polysymptomatic (complete) differs from Monosymptomatic (incomplete) Hypersomnia. *This post was originally shared on Hypersomnolence Australia website in 2015 I have since written a thorough review of the historical and current diagnostic conundrum of Idiopathic Hypersomnia and narcolepsy. The Idiopathic Hypersomnia Comprehensive Review was used as a reference by Prof Karel Šonka during the Idiopathic Hypersomnia Symposium at the World Sleep Congress 2017 in Prague. This comprehensive review follows how we have gone from the identification of Idiopathic Hypersomnia to where we are now. Drawn from 54 references, including over 40 peer-reviewed papers and book chapters on Idiopathic Hypersomnia and Narcolepsy that span more than 6 decades as well as numerous personal conversations with the world's leading Idiopathic Hypersomnia researchers. This review is also relevant if you are treating patients with Narcolepsy Type 2 (without cataplexy) or are a patient yourself.