The influence of chronic inflammation on the illnesscourse of bipolar disorder: A longitudinal study

C-reactive protein (CRP) is a systemic inflammatory marker, which indicates systemic inflammatory processes It is involved in different inflammatory processes of the body and is a reliable marker for the general inflammatory state of the body. High sensitive CRP seems to play a key role as a state and trait marker of bipolar disorder (BD). In the current study, we tried to determine the long-term effect of CRP levels on clinical symptoms and illness course of bipolar disorder.

For the current study, we examined 106 patients with BD for a period of four years. Participants underwent a clinical screening for depressive and manic episodes with the Hamilton Depression Scale (HAMD) and the Young Mania Rating Score (YMRS) and a serological diagnostic for inflammatory parameters every six months, thus leading to 8 measurement times in total. Patients with the presence of severe medical or neurological comorbidities such as active cancer, chronic obstructive lung disease, rheumatoid arthritis, systemic lupus erythematosus, Alzheimer's disease, Parkinson's disease, Huntington's disease or multiple sclerosis and acute infections were not included in the study.

In our sample, 26% showed a mean hsCRP above 5 mg/dl. Those patients showed a significantly higher mean YMRS score than those with a mean hsCRP under 5 mg/dl during our observation period. Regarding HAMD there was no significant difference in hsCRP values. The existence of lithium treatment showed no significant influence on mean hsCRP levels between the start and endpoint.

Individuals who were exposed to a higher level of inflammation over time suffered from more manic symptoms in this period. These findings underline the hypothesis that inflammatory processes have an accumulative influence on the illness course of BD, especially concerning manic symptoms and episodes.