National Sleep Foundation

Chapter 5: Circadian Rhythm Sleep Disorders


What is the prevalence of Irregular Sleep Wake Type (IST)?

The prevalence of IST is unknown, but estimates suggest it is rare.41

IST is most frequently observed as a co-morbidity with neurological dysfunction, such as in patients with Alzheimer’s disease or other forms of dementia.42


41.  Yamadera H, Takahashi K, Okawa M: A multicenter study of sleep-wake rhythm disorders: Clinical features of sleep-wake rhythm disorders. Psychiatry ClinNeurosci. 1996;50:195-201.

42.  Reid KJ and Zee PC. “Circadian disorders of the sleep-wake cycle,” in Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, pages 470-482.