A longitudinal study of fronto-limbic brain structures in patients with bipolar I disorder during lithium treatment

In order to assess the association between therapeutic response to lithium treatment and fronto-limbic brain structures' volumes in bipolar I patients (BPI) 24 BPI and 11 healthy comparisons underwent MRI scans at baseline and 4 weeks later. The BPIs received lithium during the 4 week period with a goal of achieving therapeutic blood levels of >0.5 mEq/L (mean level 0.67 mEq/L). Mood symptoms were rated with the Hamilton Depression and the Young Mania Rating Scales at baseline and after 4 weeks, and response was defined as >50% decrease on either scale. Hippocampus, amygdala, prefrontal (PFC), dorsolateral prefrontal (DLPFC), and anterior cingulate cortex (ACC) volumes were obtained by Freesurfer image analysis suite. According to baseline symptoms and treatment response, patients were assigned to three groups: euthymics (n=6), responders (n=12) and non-responders (n=6). Taken over both time periods, non-responders had smaller right amygdala than healthy comparisons and euthymic BPI (p=0.035 and p=0.003, respectively). When baseline and after treatment volumes were compared, there was a significant enlargement in left PFC and left DLPFC in BPI who responded to treatment (p=0.002 and p=0.006, respectively). Left hippocampus and right ACC volumes decreased in non-responders (p=0.02 and p=0.0001, respectively). According to the findings decreased left hippocampus and right ACC volumes may be markers of non-response to lithium amongst BPI. Smaller right amygdala may reflect symptomatic remission and be a marker of treatment non-response. Increases in left PFC and left DLPFC as a result of lithium treatment may relate to lithium's neurotrophic effects.