Possible clinical implications of slow wave sleep in major depressive disorder: a mini-review

INTRODUCTION: Major Depressive Disorder (MDD), a psychiatric disorder affecting around 3.8% of the global population, is characterized by several sleep disturbances. Alterations in slow wave sleep (SWS), a deep non-REM sleep phase, are significant for cognitive functioning and emotional memory consolidation, and its alterations are a subject of interest in MDD research.EVIDENCE ACQUISITION: A literature search, following PRISMA guidelines, was conducted on PubMed for studies published before November 2023. Twelve studies, encompassing 1375 MDD patients and 1327 healthy controls (HC), met the inclusion criteria. These studies used polysomnography to investigate sleep architecture and employed various clinical scales for depression assessment.EVIDENCE SYNTHESIS: The data show that SWS reductions are not uniformly observed in MDD patients, as only three studies reported lower SWS across the whole sample of MDD patients compared to HC. Notably, specific MDD subsets, such as patients with pronounced suicidal ideation and age- and sex-specific groups, displayed more consistent SWS reductions, suggesting developmental and hormonal influences.CONCLUSIONS: These findings indicate that SWS variations might not serve as reliable diagnostic markers for MDD due to the disorder’s heterogeneity and external factors influencing sleep patterns. However, SWS could potentially be a prognostic marker, especially for assessing disease severity and treatment response. Future research should focus on longitudinal studies with standardized methodologies to better understand SWS variations in MDD, which could lead to improved therapeutic strategies and patient outcomes in this disorder.