Little evidence for neurometabolite alterations in obsessive-compulsive disorder - A systematic review of magnetic resonance spectroscopy studies at 3 Tesla

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder that can affect individuals across the entire lifespan. Dysregulations of the cortico-striato-thalamo-cortical (CSTC) circuits may contribute to the pathophysiology of this disorder. Previous studies have used proton magnetic resonance spectroscopy (1H-MRS) to detect neurometabolic abnormalities in the CSTC circuits of OCD patients. In this study, we systematically reviewed studies that used 3 Tesla 1H-MRS to investigate neurometabolite concentrations in OCD patients versus healthy controls. We also reviewed associations between neurometabolite concentrations and symptom severity and the effect of treatment. Out of the 1161 articles that were identified by our literature search, 22 articles met our inclusion criteria for this review. Most studies did not demonstrate any neurometabolite abnormalities in OCD patients compared with controls, but some mixed results were found depending on the region of interest. The most consistent findings showed lower gamma aminobutyric acid (GABA) concentrations in the rostral anterior cingulate cortex (rACC) and higher choline concentrations in the thalamus of adult OCD patients compared to controls. Glutamate concentrations decreased after treatment in one study, but not in another. Some studies reported a correlation between neurometabolite concentrations and symptom severity, but the direction of this relation remains unclear and might be dependent on the brain region. These results do not provide strong evidence for OCD-related neurometabolite abnormalities. Because of the inconsistent results and the large heterogeneity between studies, more research is needed to investigate the exact role of neurochemistry in OCD and the utility of 1H-MRS to study it