Sleep changes in the disorder of insomnia: a meta-analysis of polysomnographic studies

Insomnia is a highly prevalent health problem worldwide. Primary insomnia (PI), i.e., insomnia not due to another disorder or substance use, represents a model to elucidate the pathophysiology of sleep. However, prior research in patients with PI has failed to demonstrate consistent abnormalities in the state-of-the-art assessment of sleep (polysomnography). The aim of this meta-analysis was to clarify whether there are identifiable polysomnographic sleep changes that correspond to the subjective complaints of patients with PI. Medline and PsycInfo databases were searched from 1994 to 2012. Effects were calculated as standardized mean differences. Studies were pooled with the random-effects metaanalytic model. Twenty-three studies met inclusion criteria. In total, 582 patients with PI and 485 good sleeper controls (GSC) were evaluated. The results showed that patients with PI present a disruption of sleep continuity and a significant reduction of slow wave sleep (SWS) and rapid eye movement (REM) sleep compared to GSC. The observed changes in sleep architecture, i.e., reductions in SWS and REM sleep, hitherto did not count among the typical polysomnographic findings in patients with PI. An advanced knowledge of the polysomnographic changes in PI may add to foster the understanding of the pathophysiology of sleep and its bi-directional relationships with somatic and mental disorders.