Objective: This study compared brain energy metabolism, as measured by cerebral concentrations of glutamate (Glu), glutamine (Gln), and N-acetyl aspartate (NAA), in older age bipolar depression (OABD) to that of psychiatrically healthy comparison subjects using proton (1H) magnetic resonance spectroscopy imaging at 4-Tesla. Metabolite levels were assessed in OABD subjects before and after 8 weeks of lamotrigine therapy with the goal of determining relationships between cerebral energy metabolism, depression symptom severity, and changes in depression symptom response.
Methods: Individuals (n = 21, mean age: 62.0 ± 5.9 years) with bipolar disorder, current episode depressed, and a healthy comparison group (n = 14, mean age: 67.5 ± 8.8 years) were selected. Participants with bipolar disorder, current episode depressed, were treated in open label fashion with lamotrigine monotherapy for 8 weeks. All subjects were scanned with 1H magnetic resonance spectroscopy at 4T at baseline and again after 8 weeks to assess levels of cerebral metabolites in the anterior cingulate cortex and parieto-occipital cortex. Metabolite levels were examined as ratios relative to creatine (Cr). Response to 8 weeks of lamotrigine treatment in the bipolar disorder, current episode depressed group, was assessed as a continuous measure on the Montgomery-Asberg Depression Rating Scale.
Results: NAA/Cr ratio in OABD was significantly lower by 14% (95% confidence interval: [1%, 26%]) than in comparison subjects at baseline. However, there were no associations between NAA/Cr, Glu/Cr, or Gln/Cr and either depression severity or lamotrigine treatment.
Conclusion: Group differences in NAA suggest evidence for a deficit in cerebral energy metabolism in OABD.
Keywords: Geriatric; NAA (N-acetyl aspartate); bipolar depression; lamotrigine; proton magnetic resonance spectroscopy.
Copyright © 2019. Published by Elsevier Inc.