Increased thalamic N-acetylaspartate in male patients with familial bipolar I disorder

N-Acetylaspartate (NAA) in the anterior and mediodorsal thalamic regions was measured using proton magnetic resonance spectroscopic imaging (1H-MRSI) in 15 euthymic male patients with familial bipolar I disorder and compared to values in 15 male control subjects to determine if there was evidence for altered neuronal/axonal integrity. MRI tissue segmentation methods were also utilized to obtain tissue-contribution estimates for each MRSI voxel. Relative to the comparison group, the patients with bipolar I disorder demonstrated significantly higher NAA and creatine in both the right and left thalamus. NAA was also significantly higher in the left thalamus compared to the right in both bipolar I patients and controls. There were no group or lateralized differences in the percentages of different tissue types within the MRSI voxels, suggesting that the thalamic NAA and creatine alterations were not an artifact of variations in tissue type percentages in the MRSI voxels. There was also no significant association between NAA or creatine and illness duration. The findings of increased thalamic NAA bilaterally may represent neuronal hypertrophy or hyperplasia, reduced glial cell density, or abnormal synaptic and dendritic pruning. Increased thalamic creatine bilaterally may represent altered cellular energy metabolism and is consistent with prior studies demonstrating changes in thalamic metabolism in mood disorders.