Association between autoimmune thyroiditis and depressive disorder in psychiatric outpatients

Thyroid diseases are often associated with psychiatric disorders. The prevalence of autoimmune thyroiditis in the general population is estimated to be at about 5-14 %. A clinical study was conducted to evaluate the association between autoimmune thyroiditis and depression in psychiatric outpatients. Fifty-two patients with depression and nineteen patients with schizophrenia (serving as control group), attending a psychiatric outpatient unit, were included. In addition to the measurement of thyroid-stimulating hormone (TSH), free triiodothyronine, free thyroxine, antithyroid peroxidase (anti-TPO) antibodies, and anti-thyroglobulin antibodies, ultrasound examination of the thyroid gland was performed. The proportion of pathologically increased anti-TPO levels in patients with depression was high. Furthermore, the distribution of pathologically increased anti-TPO levels was significantly (χ (2) = 5.5; p = 0.019) different between patients with depression (32.7 %) and patients with schizophrenia (5.3 %). In a gender- and age-adjusted logistic regression, the odds ratio of uni- or bipolar patients with depression for an autoimmune thyroiditis was ten times higher (95 % CI = 1.2-85.3) when compared with schizophrenia patients. TSH basal level did not differ between patients with depression and patients with schizophrenia. Our study demonstrates a strong association between anti-TPO levels, which are considered to be of diagnostic value for autoimmune thyroiditis (in combination with a hypoechoic thyroid in ultrasonography) with uni- or bipolar depression. It should be noted that the routinely measured TSH level is not sufficient in itself to diagnose this relevant autoimmune comorbidity.