Background: Magnetic resonance spectroscopy studies (MRS) reported abnormally low levels of N-acetylaspartate (NAA, a marker of neuronal integrity) in dorsolateral prefrontal cortex (DLPFC) of adult bipolar patients, suggesting possible neuronal dysfunction. Furthermore, recent MRS reports suggested possible lithium-induced increase in NAA levels in bipolar patients. We examined with in vivo (1)H MRS NAA levels in the DLPFC of adult bipolar patients.
Methods: Ten DSM-IV bipolar disorder patients (6 lithium-treated, 4 drug-free) and 32 healthy controls underwent a short echo-time 1H MRS session, which localized an 8 cm3 single-voxel in the left DLPFC using a STEAM sequence.
Results: No significant differences between the two groups were found for NAA, choline-containing molecules (GPC+PC), or phosphocreatine plus creatine (PCr+Cr) (Student t-test, p > 0.05). Nonetheless, NAA/PCr+Cr ratios were significantly increased in lithium-treated bipolar subjects compared to unmedicated patients and healthy controls (Mann-Whitney U-test, p < 0.05).
Limitations: Relatively small sample size may have reduced the statistical power of our analyses and the utilization of a single-voxel approach did not allow for the examination of other cortical brain areas.
Conclusions: This study did not find abnormally reduced levels of NAA in left DLPFC of adult bipolar patients, in a sample of patients who were mostly on medications. However, elevated NAA/PCr+Cr ratios were shown in lithium-treated bipolar patients. Longitudinal 1H MRS studies should further examine NAA levels in prefrontal cortex regions in untreated bipolar patients before and after mood stabilizing treatment.