Background: We tested for differences in temporal lobe volume in bipolar disorder and the relationship between these volumes and psychotropic medication use.
Methods: 125 subjects with bipolar disorder and 87 comparison subjects with no psychiatric illness completed clinical interviews and 1.5T MRI brain scans. Temporal lobe volumes were manually traced and segmented into gray matter and white matter volumes using an automated process. General linear models examined the relationship between these volumes and diagnosis as the primary predictor with age, sex, education, and race as copredictors. Secondary analyses incorporated the use of psychotropic medication into the linear models, and parsimonious models developed through backwards regression.
Results: In initial models, subjects with bipolar disorder exhibited larger temporal lobe white matter bilaterally (left: F(1,211)=2.86, p=0.0047; right: F(1,211)=3.25, p=0.0014). Current antipsychotic use was significantly associated with larger bilateral temporal lobe white matter volumes (left: F(2,211)=9.45, p=0.0001; right: F(2,211)=10.79, p<0.0001), wherein bipolar subjects taking antipsychotics had larger volumes than bipolar subjects not taking antipsychotics or healthy comparison subjects. Temporal lobe gray matter volume was not significantly associated with diagnosis or medication use.
Limitations: Excluding subjects with substance use disorders may limit the study's generalizability.
Conclusions: These findings indicate that differences in temporal lobe white matter are associated with bipolar disorder and use of antipsychotic medications.