Hypothalamic–pituitary–thyroid-axis function in treatment resistant depression

Recently, there were some reports that the prevalence of various grades of hypothyroidism may be increased in patients with treatment resistant depression (TRD). The aim of the present study was to examine serum basal thyroid-stimulating hormone (TSH) and thyroxine (T4) levels in 36 major depressed subjects, of whom 27 had TRD and 15 were normal volunteers. There were no significant differences in serum basal TSH or T4 levels between major depressed subjects and normal controls, or between patients with TRD versus normal controls or subjects without TRD. There was a trend towards lower serum basal T4 concentrations in patients with TRD than in other depressed patients and normal controls. One patient with TRD had basal serum TSH levels in the hyperthyroid range. Two subjects, one with TRD and one normal control, had serum TSH values in the subclinical hypothyroid zone, but their serum T4 values were in the euthyroid range. There were no significant relationships between basal TSH or T4 and severity of illness, staging of depression based on prior treatment non-response, length of the depressive episode, duration of illness, or number of previous depressive episodes. In conclusion, the results of this study do not provide evidence that (subclinical) hypothyroidism occurs more than coincidentally in depressed patients with TRD.