Diagnosing Idiopathic Hypersomnia
The pathogenesis (the mechanism that causes a disease) of IH is not well understood, therefore a diagnosis of IH can sometimes take many years. During this time patients can be misdiagnosed and incorrectly treated or ignored altogether and dismissed as being lazy. Many other conditions produce excessive daytime sleepiness and must be ruled out as a cause for the excessive sleepiness before a diagnosis of IH can be considered. These include sleep disordered breathing syndromes (eg: sleep apnea), periodic limb movements, insufficient sleep, psychiatric disorders, medication effects, circadian rhythm disorders and medical illness. Other tests including blood tests are necessary to exclude medical conditions such as hypothyroidism.
The diagnosis of IH is based on clinical features, exclusion (excluding all other possible causes of a patients excessive daytime sleepiness - EDS), and a combined polysomnography (sometimes referred to as an “overnight sleep study”)/Multiple Sleep Latency Test (MSLT). This procedure allows sleep apnea, upper airway resistance syndrome, narcolepsy, periodic leg movements, and sleep fragmentation to be ruled out as causes of a patient's EDS.
There are various diagnostic manuals used throughout the world to diagnose Idiopathic Hypersomnia including the The Diagnostic and Statistical Manual of Mental Disorders (currently the DSM5) and the International Classification of Sleep Disorders (currently the ICSD3). In Australia diagnosing IH does not rely on fitting particular diagnostic criteria from such manuals. Australian Sleep Specialists follow guidelines written by the ASA (Australian Sleep Association) and the TSANZ (Thoracic Society of Australia and New Zealand) – “Guidelines for Sleep Studies in Adults (2014)”. "All Australian sleep study reports should be consistent with the ASA guidelines and the AASM (American Academy of Sleep Medicine) Manual for the Scoring of Sleep and Associated events as qualified by the ASTA (Australian Sleep Technologists Association)/ASA Commentary (2010)" - Standard for Sleep Disorders Services ASA June 2012.
ASA & TSANZ Guidelines for Sleep Studies in Adults 2014.
ASA Standard for Sleep Disorders Services June 2012.
ASTA/ASA Commentary on AASM Manual for the Scoring of Sleep and Associated Events December 2010