Depressive episodes have no additional impact on cognition in patients early in the course of bipolar disorder, research suggests.
In common with previous findings, the researchers identified impaired cognition in 68 patients with first-episode mania relative to 38 controls, all of whom were participants of the Systematic Treatment Optimization Programme for Early Mania (STOP-EM).
However, cognition was not further impaired in patients with previous depressive episodes relative to those without and, moreover, it did not worsen more in patients who had a depressive episode during the following year than in those who did not.
“[I]t is possible that cognitive deficits in early bipolar disorder, immediately after recovery from a first manic episode, are likely determined by the first manic episode and not depressive episodes”, say study author Lakshmi Yatham (University of British Columbia, Vancouver, Canada) and co-workers.
All study participants undertook relevant subtests from the Cambridge Neuropsychological Test Automated Battery revealing the patients to have significantly impaired function, relative to the controls, in all domains tested (processing speed, attention, verbal and nonverbal memory, working memory and executive function).
However, the 33 patients with mania who had experienced at least one episode of depression (average of 2.2) did not have poorer cognitive function than the 35 patients without previous depression.
During 1 year of follow-up, 24 patients had no recurrent mood episodes and 15 had a depressive episode. The other patients either had both manic and depressive episodes or did not complete follow-up. During follow-up, cognitive function declined slightly, but no more among patients with than without recurrent depression.
However, patients with recurrent depression had significantly poorer verbal memory at the start of follow-up than those without, the team reports in the British Journal of Psychiatry. They also had higher scores on the Hamilton Rating Scale for Depression-29 at baseline, but the difference in verbal memory persisted after accounting for this, suggesting that it “may serve as a marker for increased susceptibility to depressive recurrence early in the course of bipolar disorder.”
The researchers note that this is consistent with the reported links between depression, memory and hippocampal functioning, and say this would be interesting to address in a neuroimaging study.
They also caution that their study does not “rule out the possibility that further depressive episodes may occur with illness progression and could contribute to more deficits in hippocampus functioning and cognitive decline subsequently”.
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