Is It Possible to Establish Thresholds for Depressive Symptom Severity Associated With Cognitive Impairments in...

Individuals with bipolar disorders (BDs) with depressive symptoms exhibit poorer cognitive performance and are often excluded from procognitive interventions and cognitive research. Threshold values on depression severity scales, based on cutoffs defining depressive episodes, have traditionally been used to exclude patients suspected of having depression-associated cognitive impairment. Identifying a threshold value for depression-associated cognitive impairment on these scales could help guide patient selection and treatment. We assessed neuropsychological performance in outpatients with BD with varying levels of depressive symptom severity measured by the Montgomery-Åsberg Depression Rating Scale (MADRS). The sample was divided based on the total MADRS score or subscores in MADRS theoretical domains. We then compared average cognitive performance between groups while adjusting for relevant covariates to determine a MADRS score above which cognition is significantly impaired. We included 2532 individuals with BD. The composite cognitive score was significantly lower in individuals with a MADRS score ≥ 12 than in those with a score ≤ 1 but did not differ from that of individuals with scores between 2 and 11. Symptoms of detachment and sadness were more strongly associated with cognitive impairment than other symptoms. Individuals with type I BD with MADRS detachment subscores higher than 4 and individuals with type II BD with nonzero sadness subscores had significant cognitive impairment compared to individuals with lower subscores. Excluding individuals with BD whose cognition may be affected by depressive symptoms would require omitting those with MADRS detachment subscores higher than 4 or nonzero sadness subscores. Our findings question the existence of a total depression severity threshold for cognitive impairment, as specific depressive symptoms seem more strongly associated with cognitive impairment than total symptom severity.