Objective sleep markers to differentiate unipolar and bipolar depression: A systematic review and meta-analysis

Differentiate between unipolar and bipolar depression through studies investigating objective sleep markers using polysomnography and actigraphy.

Studies comparing unipolar and bipolar depression using objective markers often lack power and present heterogeneous results. However, in a recent actigraphy study (Leseur et al., 2024), which included 66 patients with unipolar depression and 24 with bipolar depression, notable and encouraging variations in sleep markers were found between the two disorders. Specifically, a decrease in sleep duration and efficiency was observed in people diagnosed with depression compared to those diagnosed with bipolar depression.

Currently, there is a major challenge in distinguishing between unipolar and bipolar major depressive episodes. A significant body of research has been dedicated to identifying biomarkers that can aid in this differentiation due to its crucial implications, particularly for therapeutic and prognostic purposes. Among the biomarkers of interest, markers related to sleep and circadian rhythms show promise and could potentially aid in making this distinction. A few studies have evaluated these markers objectively, but they often lack power, or the results stay highly heterogeneous. We conducted a systematic review and meta-analysis of published studies comparing sleep disorders between unipolar or bipolar depression using PubMed, Cochrane Library, and Web of Science databases. Actigraphy, polysomnography, and nocturnal Electroencephalography (EEG) were considered. The qualitative analysis retained 11 original studies, including 666 participants (355 patients diagnosed with bipolar depression and 311 with unipolar depression) and 8 studies were included for the meta-analysis. Depression in unipolar disorder was associated with a shorter total sleep time (SMD -0.3539, [CI: -0.5486 to -0.1592]; p < 0.001; MD: -27.9592; I² = 0 %) and a poorer sleep efficiency (SMD -0.3105, [95 % CI: -0.5207 to -0.1003]; p = 0.004; MD: -0.3105; I² = 0 %) than patients diagnosed with bipolar depression. There were no significant differences between the two groups in sleep onset latency, REM latency and REM % during the night. In summary, when examining objective sleep markers through polysomnography or actigraphy to distinguish between the two disorders, it appears that unipolar depressive disorder is associated with a reduced total sleep time and a poorer sleep efficiency than bipolar depressive disorder. These findings have substantial implications for identifying individuals with either unipolar or bipolar disorder using objective sleep markers, as well as for crafting tailored and effective therapeutic approaches.