Elevated C-reactive protein and cognitive deficits in individuals with bipolar disorder

Background: Some individuals with bipolar disorder have cognitive deficits even when euthymic. In previous studies, we found an association between elevated levels of C-reactive protein (CRP), a marker of inflammation, and reduced cognitive functioning in schizophrenia. This issue has not been examined in bipolar disorder.

Methods: We measured the levels of high sensitivity CRP in serum samples from 107 individuals with bipolar disorder. Cognitive functioning was measured with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Trail Making Test Part A and WAIS Information and Letter Number Sequencing. We estimated the odds of RBANS scores <=70 for participants whose CRP levels were above the 75th and the 90th percentile of the level of non-psychiatric controls. We also examined the association between cognitive scores and CRP levels. Covariates included demographic factors, mood symptom severity, cigarette smoking status, and body mass index.

Results: There was a significantly increased odds of low RBANS total score for individuals who had a CRP level higher than the 90th percentile (OR=4.32, p=.018) and the 75th percentile (OR=3.07, p=.04)) of the control group. There was an inverse relationship between CRP levels and performance on RBANS total (t=-2.48, p=.015); RBANS immediate memory (t=-2.16, p=.033); RBANS attention (t=-2.18, p=.032); RBANS language (t=-2.13, p=.036); Trail Making A (t=-2.39, p=.019).

Limitations: Factors which we did not measure such as diet, allergen exposure, and underlying autoimmune disorders may contribute to CRP levels.

Conclusions: Inflammation may play a major role in the cognitive deficits associated with bipolar disorder.