The hypothalamic-pituitary-thyroid axis in major depression.

We investigated the capacity of several thyroid-axis measures to distinguish between depressed and control subjects and determined whether these variables were related to antidepressant treatment response. We studied 105 subjects who fulfilled the DSM-III-R criteria for a current major depressive episode and 41 volunteers with no current mental disorder. The following thyroid-axis variables were measured: difference between T4 levels at 09.00 hours and 13.00 hours; baseline TSH; maximal TSH response to 400 micrograms TRH (delta max TSH); and presence of a blunted delta max TSH. The T4 difference variable alone distinguished between depressed and control subjects. In multivariate analyses, T4 difference and delta max TSH were independently related to antidepressant-treatment outcome, and predicted a modest proportion (14%) of the variance in outcome. The relationship between these two variables and treatment outcome was particularly strong in depressed male subjects who were receiving desipramine, for whom they accounted for 36% of the variance in treatment outcome. The T4 difference variable both distinguished between depressed and control subjects and was related to treatment outcome. Although this finding requires replication, it is consistent with other reports of the usefulness of thyroid-axis indices measured at different times of day in depressed patients.