Neurodevelopmental factors play key role in cognitive deficits in bipolar patients
Cognitive deficits in bipolar disorder are neurodevelopmental rather than neurodegenerative in nature, a recent study has reported. Furthermore, cognitive impairment in bipolar patients appears to be stable, in the majority at least.
Researchers performed a systematic review and meta-analysis of 22 studies reporting longitudinal neurocognitive data in bipolar disorder with a minimum follow-up duration of 1 year. They weighted effect sizes using the random-effects inverse variance method, assessed homogeneity using the I2 test, and estimated publication bias using funnel plot asymmetry with Egger’s test.
Pooled data from 643 patients with bipolar disorder showed no change in cognition over time in the short-term (median duration, 1.5 years) and long-term (median duration, 5.5 years) follow-up. On the contrary, there was evidence for modest task performance improvements in memory and working memory.
Further analysis of cognitive changes in bipolar patients vs healthy controls (459 bipolar vs 367 healthy controls) and schizophrenia (172 bipolar vs 168 schizophrenia) revealed a similar trajectory of cognitive functioning between bipolar patients and healthy controls and schizophrenic patients.
Researchers noted that the lack of evidence of cognitive deterioration at follow-up in bipolar patients, with improvements even observed in task performance in some cognitive domains, does not support the notion of progressive cognitive deficits occurring in bipolar disorder.
The distribution of effect sizes was significantly homogeneous for all cognitive measures with the exception of executive functions. Additionally, there was no evidence of publication bias for any cognitive measure.
Bipolar disorder has been associated with cognitive deficits in a number of domains such as executive functions, processing speed, attention, memory and social cognition. The cognitive impairment in bipolar disorder is reported to be less severe compared with deficits observed in schizophrenia, although both disorders have similar cognitive profile. [Medicine 2008;38:771–785; Psychological Medicine 2017;47:1030–1040; Schizophrenia Research 2005;80:137–149]