Abstract
<title>Abstract</title> <p>Background Obsessive-compulsive symptoms (OCS) frequently co-occur with bipolar disorder and may exacerbate depressive symptoms and worsen prognosis. However, the neurobiological mechanisms underlying OCS in adolescents with bipolar II disorder (BD-II) remain poorly understood. This study compared neurometabolic profiles of the ventromedial prefrontal cortex (vmPFC) between BD-II adolescents with and without OCS, and examined their correlations with clinical features. Methods A total of 84 participants were included in this study, comprising 28 patients with a BD-II depressive episode accompanied by OCS (BD-II-OCS), 30 patients with a BD-II depressive episode without OCS (BD-II-non-OCS), and 26 healthy controls (HC). Clinical symptoms were assessed using the 24-item Hamilton Depression Rating Scale (HDRS-24), the Young Manic Rating Scale (YMRS) and the Child Yale-Brown Obsessive-Compulsive Scale (CY-BOCS), while ¹H-magnetic resonance spectroscopy (¹H-MRS) was used to measure the ratios of N-acetylaspartate/creatine (NAA/Cr), choline/creatine (Cho/Cr), inositol/creatine (mI/Cr) and glutamate + glutamine/creatine (Glx/Cr) in the vmPFC. Results Compared with the HC group, the NAA/Cr ratio was significantly lower in both BD-II groups, with the BD-II-OCS group showing a lower value than the BD-II-non-OCS group. The Glx/Cr ratio in the BD-II-OCS group was also significantly lower than that in the BD-II-non-OCS group and the HC group. Furthermore, patients in the BD-II-OCS group had a longer disease duration than those in the BD-II-non-OCS group. Within the BD-II-non-OCS group, the Glx/Cr ratio was negatively correlated with HDRS scores. Receiver operating characteristic (ROC) analysis indicated that the NAA/Cr ratio demonstrated good discriminatory power in distinguishing the BD-II-OCS group from both the HC group and the BD-II-non-OCS group. Conclusion Adolescents with BD-II depressive episodes accompanied by OCS exhibit more pronounced impairment in vmPFC neuronal integrity and reduced glutamatergic metabolism. The NAA/Cr ratio shows some potential for distinguishing this subtype; neurometabolic markers may serve as an auxiliary reference for distinguishing adolescent bipolar disorder with OCS from those without OCS, although their value requires further validation in studies with larger sample sizes.</p>