Bidirectionality between sleep symptoms and core depressive symptoms and their long-term course in major depression

Objective: To investigate the bidirectional dynamic relationship between sleep symptoms and core depressive symptoms and to identify subgroups differing with respect to their course. 

Methods: The weekly state of depressive symptoms in depressed primary care patients (N = 267) was assessed retrospectively every 3 months for 3 consecutive years. The bidirectional relationship between sleep and core symptoms was estimated by means of manifest Markov modeling. Data-driven subgroups were estimated with parallel processes-latent class growth analyses to identify differences in courses of sleep and core symptoms. 

Results: In total, core symptoms were associated with next-week development (odds = 1.42; 95% confidence interval [CI] = 1.20-1.67; p < .001) and remission of sleep symptoms (odds = 0.86; 95% CI 0.75 to 0.99, p = .033). Evidence was also found for a reverse pathway such that sleep symptoms were associated with the development (odds = 1.26; 95% CI = 1.05-1.50; p = .012) and remission of core symptoms (odds = 0.87; 95% CI = 0.76-0.99; p = .038). Three classes with different 3-year courses were derived. In class 1, the likelihood that core symptoms remitted was reduced if sleep symptoms were present, and symptoms remained present over 3 years. In class 2, symptoms were bidirectionally related and remitted over 3 years. In class 3, symptoms were not associated, and sleep symptoms declined less steeply than core depressive symptoms. 

Conclusions: The results suggest that sleep symptoms should be treated alongside core depressive symptoms in patients with an asynchronic decrease of sleep and core symptoms and in patients that do not respond to treatment to increase the chance of complete remission.