Prolongation of REM Sleep Latency in Nightmare Disorder May Indicate Subtle REM Sleep Fragmentation and Decreased REM Sleep Propensity

Abstract

Journal of Clinical Sleep Medicine, Vol. 14, No. 8 August 15, 2018 Creamer and colleagues1 have addressed the very important topic of the high prevalence of clinically significant nightmares (31.2% of 473 military personnel met criteria for nightmare disorder [NDO] and endorsed trouble falling asleep because of bad dreams on at least a weekly basis) among military personnel, with possibly only a minority receiving medical attention, as only 3.9% endorsed nightmares as their reason for visit. In their commentary on this research, Collen and colleagues2 have further emphasized that nightmares tend not to receive adequate clinical attention, with decreased reporting by patients being an important barrier to treatment. Both have stressed the importance of addressing nightmares, as they are associated with greater psychiatric comorbidity including a higher suicide risk.1,2 Creamer and colleagues examined the clinical and polysomnographic correlates of NDO: polysomnographically the only sleep physiologic parameters that were significantly different between NDO (n = 154) versus non-NDO (n = 339) groups were sleep onset latency (minutes) (16.6 ± 21.9 versus 12. ± 16.0, P = .016) and rapid eye movement (REM) sleep latency (minutes) (145 ± 74.3 versus 126 ± 63.2, P = .012), which were both relatively more prolonged in the NDO versus non-NDO groups respectively. There are several potential confounding factors in this study including greater psychiatric comorbidity (eg, posttraumatic stress disorder [PTSD], depression, anxiety) in the NDO-group and insufficient information on medications that can affect REM sleep.1,2 Nightmares have been associated with a disruption of “REM pressure” or a low REM sleep propensity3 and less resiliency of REM sleep as evidenced by a more extreme first night effect.3 This in turn can be associated with a relative prolongation of the REM sleep latency.3 REM sleep propensity is directly related to the percent of total sleep that is REM sleep which was not significantly different between the NDO and non-NDO groups.1 It is possible that the significantly prolonged REM sleep latency in the NDO group, in the absence of other markers such as a decrease in percent of total REM sleep, reflects early and subtle fragmentation of REM sleep in NDO (which can become more marked in disorders associated with more frequent and severe nightmares, eg, PTSD4). A relative prolongation of REM sleep latency in NDO may be an early marker of decreased REM sleep LETTERS TO THE EDITOR