Elevated choline in dorsolateral prefrontal cortex of lithium responders with bipolar I disorder

Response to lithium maintenance varies widely across patients with bipolar disorder (BD). The studies on neurochemical correlates of long-term lithium response in BD remain scant.

To assess the neurochemical profile in DLPFC based on lithium response status among subjects with bipolar I disorder (BD-I) using in vivo MRS.

This was an observational study of 40 right-handed, euthymic adult participants with DSM-5 BD-I on long-term lithium maintenance with no psychiatric comorbidities (MINI 7.0). Using Alda Lithium Response Scale (LRS), a cut-off ≥ 7 for excellent lithium response, the sample was grouped into study group I for responders and group II for non-responders. All participants were assessed using NIMH Life Chart Method and IGSLI typical/atypical features scale. ¹H-MRS was carried out on a 3 T MR scanner (Achieva, Phillips) using a 32-channel head coil, with a voxel placed at the left DLPFC. LC model was used to measure absolute concentrations of neurochemicals and their ratios in relation to creatine.

Group I (n = 20) was comparable to Group II (n = 20) with respect to demographic and illness profile. The GPC/Cr+PCr ratio was significantly higher (p = 0.028) among excellent lithium responders (0.32 ± 0.20 mmol/l) compared to sub-optimal responders (0.25 ± 0.05 mmol/l). Choline-containing compounds reflect alterations in cell membrane synthesis or myelin turnover, and are a marker of overall cell density. No significant alterations were detected in NAA, glutamate, glutamine, myo-inositol and creatine.

The lithium responders exhibited elevated choline (GPC) in the left DLPFC compared to non-responders.