Objective: The neurophysiological basis of bipolar disorder in youths remains poorly understood. Neurofunctional and neuropathologic studies have implicated the amygdala as a primary brain structure involved in the regulation of emotion. Because one of the cardinal features of bipolar disorder is mood dysregulation, structural and functional amygdala abnormalities identified with neuroimaging may serve as useful disease and treatment response biomarker. Therefore, we conducted a meta-analysis summarizing the literature examining amygdala size obtained from magnetic resonance imaging in bipolar youths and adults.
Method: A literature search using the National Institutes of Health's PubMed was conducted to identify published peer-reviewed neuroimaging studies of amygdala size in children, adolescents, and adults with bipolar disorder. Eleven studies that met inclusion and exclusion criteria were identified.
Results: Smaller amygdala volumes were found in children and adolescents with bipolar disorder compared with the control children and adolescents (standardized mean difference -0.74; 95% confidence interval -1.36 to -0.15). Amygdala volumes in bipolar adults were not significantly different from the control adults (standardized mean difference 0.20; 95% confidence interval -0.31 to 0.73).
Conclusions: The results of this meta-analysis suggest that structural amygdala abnormalities are present in bipolar youths but that these structural differences do not seem to be present in bipolar adults. Future studies examining whether structural, functional, and neurochemical amygdala differences between bipolar and control youths may be useful as age-specific biomarkers of illness and treatment response are needed.