A prospective study confirms the detrimental effect of subthreshold depressive symptoms on the outcomes of patients with bipolar disorder.
The findings, published in the Journal of Affective Disorders, also suggest that the effect is partly mediated by cognitive impairment.
Researcher Anabel Martínez-Arán (University of Barcelona, Spain) and colleagues say that most studies have been cross-sectional, whereas they followed up 111 patients for 1 year. The patients were aged an average of 40 years and 78.4% had bipolar I disorder; all were euthymic at inclusion.
The team assessed verbal memory (using the California Verbal Learning Test), because impairment in this neurocognitive function is thought to be a core feature of bipolar disorder. Along with subsyndromal depressive symptoms (≤8 on the Hamilton Depression Rating Scale), patients’ composite verbal memory score explained 19% of the variance in their baseline scores on the Functioning Assessment Short Test (FAST).
Subthreshold depressive symptoms and verbal memory were associated with each other, such that patients with more depressive symptoms had larger memory impairments. They were also individually associated with baseline functional status.
“Thus in bipolar disorder, depressive symptoms are not only negatively associated with the outcome, but also affect verbal memory performance,” say the researchers.
Verbal memory had a significant indirect effect on outcome, partly mediating the relationship between depressive symptoms and functional status.
During 1 year of follow-up, patients’ functional status remained fairly stable overall, with average FAST scores of 29 at baseline and 27 at follow-up. Baseline functional status explained 44% of the variance in 1-year functional outcomes.
As baseline functional status was, in turn, partly dependent on depressive symptoms and verbal memory, these variables therefore contribute to follow-up functional outcomes, explain Martínez-Arán et al.
The researchers note, however, that the study only assessed verbal memory, and impairments in this domain could be partly caused by other neurocognitive deficits.
“The identification of mediators in the prediction of functional outcome may help to disentangle the complex network of variables that contribute to functional outcome, since many variables with direct and indirect effects might be involved,” they conclude.
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