Sleep disturbances and depression severity in patients with Parkinson's disease

Objectives: Parkinson's disease (PD) is a multisystem movement disorder associated with sleep disturbance and depression. Sleep disturbances and depression severity share a bidirectional association. This association may be greater in individuals who are more vulnerable to the deleterious consequences of sleep disturbance and depression severity. We investigated whether the association between sleep disturbances and depression severity is greater in patients with PD than in matched controls (MC). Materials and Methods: The study sample (N = 98) included 50 patients with idiopathic PD and 48 age-, race-, sex-, and education-matched controls. Sleep disturbances were assessed using self-reported total sleep time (TST) on the Pittsburgh Sleep Quality Index, the sleep item on the Beck Depression Inventory, 2nd ed. (BDI-II), and the Insomnia Severity Index total score. Depression severity was assessed using the BDI-II total score, excluding the sleep item. Spearman's correlations, chi-squared tests, and multiple regression were used to assess associations between sleep disturbances and depression severity in PD and MC. Fisher's Z transformation was used to test whether the association between sleep disturbances and depression severity was stronger in patients with PD. Results: Shorter TST, sleeping less than usual, and insomnia severity were associated with depression severity in the total sample, r(s)(94) = -0.35, p = .001; r(s)(71) = 0.51, p < .001; r(s)(78) = -0.47, p < .001; r(s)(98) = 0.46, p < .001, respectively. The association between shorter TST and depression severity was greater in patients with PD than it was in MC, p < .05. Conclusion: Short TST may be an important marker, predictor, or consequence of depression severity in patients with Parkinson's disease.