Clinical characteristics of thyroid structure and functional abnormalities in bipolar disorder and their association with mood symptoms: a retrospective cross-sectional study

Abstract Background This study aimed to investigate the association between thyroid abnormalities (both structural and functional) and bipolar disorder (BD), and to evaluate the relationship between thyroid parameters and mood symptom severity. Methods In this retrospective cross-sectional study of clinical records (January 2022 to December 2024), data from 593 participants (398 BD patients and 195 healthy controls) were reviewed. Thyroid structure was evaluated via ultrasound (nodules, size), and function was assessed by measuring nine serum parameters, including thyroid hormones and autoantibodies. Clinical symptoms were rated using standardized scales. Statistical analyses employed logistic regression to determine associations and Spearman correlation to assess links with symptom scores. Results Compared to controls, the BD group had a higher prevalence of structural abnormalities, lower TT3/TT4, elevated TSH, and higher rates of positive TgAb and TPOAb. Multivariate analysis indicated a protective effect of nodules, normal/elevated TT3/TT4/TG, and positive TgAb on outcomes, though some associations lost significance. Correlation analysis revealed no significant relationship between thyroid parameters and mood scale scores. Conclusions Thyroid structure and function abnormalities were associated with BD in this retrospective analysis, although several associations were attenuated after multivariable adjustment. However, no significant cross-sectional correlation with the severity of manic or depressive symptoms was found, underscoring the complexity of this relationship and the need for further mechanistic investigation. Clinical trial number Not applicable.