Factors that predispose, prime and precipitate NREM parasomnias in adults: clinical and forensic implications.

Sleepwalking and related disorders are the result of factors that predispose, prime and precipitate episodes. In the absence of one or more of these factors sleepwalking is unlikely to occur. Predisposition to sleepwalking is based on genetic susceptibility and has a familial pattern. Priming factors include conditions and substances that increase slow wave sleep (SWS) or make arousal from sleep more difficult. These factors include sleep deprivation, alcohol, medications, situational stress and fever among others. The patient with a genetic predisposition to sleepwalking and with priming factors still requires a precipitating factor or trigger to set the sleepwalking episode in motion. Classical theories of sleepwalking were based primarily on case reports. Recently some of these theories have been tested in the sleep laboratory. Experimental sleep deprivation studies of sleepwalkers generally report an increase in complex behaviors during SWS, although one prominent study reported the opposite effect. However, the generally accepted theory that alcohol and medications can induce sleepwalking episodes remains entirely based on clinical and forensic case reports. Alleged cases of alcohol related sleepwalking often involve individuals lacking the generally accepted characteristics of sleepwalkers but with very high blood alcohol levels that could in and of itself account for complex behaviors noted without the presence of sleepwalking. Further, the effects of high levels of alcohol dramatically decrease SWS, a finding inconsistent with sleepwalking. Case reports of medication-related induction of apparent sleepwalking most often present a complex medical and psychiatric history associated with multiple medications. These patients often lack the clinical history and other criteria currently required for the diagnosis of sleepwalking. The medication-related behaviors may instead represent some other condition in an awake, but impaired patient. Sleep laboratory research has identified sleep disordered breathing, periodic leg movements, noise and touch among others as proximal triggers of sleepwalking episodes. Treatment of these triggers may result in resolution of sleepwalking without medication. Further sleep laboratory research is needed before experimental findings can be used for routine diagnostic and forensic purposes.