Body position changes and periodic movements in sleep

What triggers episodes of periodic movements in sleep (PMS) remains unknown. Despite the uncertainties, there is no doubt of the widespread prevalence of PMS, particularly in elderly populations. This study explored possible consistent temporal relationships between body position and PMS episodes. Eleven subjects, monitored by polygraph and videotape, averaged 299 leg jerks in nine episodes, and 13 body position changes of greater than or equal to 90 degrees. Leg jerk episodes had a significant tendency to terminate soon before body position changes, and likewise there was a trend for leg jerk episodes to begin soon after position changes. It is hypothesized that adverse body positioning, via an influence upon the spinal cord or peripheral tissue perfusion, triggers PMS episodes, which persist until the adverse positions are changed. In this small sample, "adverse" positions could not be elucidated.