Association between thyroid function and comorbid anxiety in first-episode and drug naïve patients with major depressive disorder.

Objective: Existing studies have shown that thyroid dysfunction is associated with depression. However, its role in major depressive disorder (MDD) with comorbid anxiety remains unclear. The main purpose of this study was to compare thyroid function in a large sample of first episode drug naïve (FEDN) MDD patients with and without anxiety.

Methods: This cross-sectional study examined 1718 outpatients who were drug-naïve and diagnosed as MDD at first episode. Socio-demographic and clinical data, as well as thyroid function-related parameters, including free thyroxine (FT4), free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin (TGAb), were evaluated. The Hamilton Depression Rating Scale (HAMD), Hamilton Anxiety Rating Scale (HAMA) and the positive subscale of the Positive and Negative Syndrome Scale (PANSS) were used to evaluate depressive, anxiety and psychotic symptoms, respectively.

Results: Compared to MDD patients without anxiety, MDD patients with anxiety were more likely to have more suicide attempts and psychotic symptoms, as well as higher serum levels of TSH, TPOAb and TGAb (all p < 0.001). Among patients with abnormally elevated serum TSH, TPOAb, and TGAb, 83.5% (872/1044), 89.3% (391/438) and 89.6% (266/297) had comorbid anxiety disorders, respectively. The odds ratio between patients with comorbid and without comorbid anxiety was 1.657 (95% CI 1.304-2.105) for elevated TSH levels, 1.943 (95% CI 1.444-2.613) for elevated TGAb levels, and 2.448 (95% CI 1.760-3.403) for elevated TPOAb levels. Furthermore, multivariable linear analysis showed that elevated TSH and TGAb were significant predictors of anxiety in MDD patients.

Conclusions: Our results suggest that comorbid anxiety in FEDN MDD patients is positively associated with elevated TSH and TGAb levels, which may be promising biomarkers of comorbid anxiety in MDD patients. Clinical treatment of impaired thyroid function may be useful for comorbid anxiety in MDD patients.