Basal thyrotropin and major depression: relation to clinical variables and treatment outcome

There is a current argument in thyroidology about whether the normal range for basal thyrotropin (TSH) is too broad. Some groups suggest that a TSH of less than 2.5 mIU/L is a better cut-off for euthyroidism. Because major depression is associated with changes in thyroid hormone status and thyroid hormones may be an effective treatment for major depression, we examined whether TSH levels above or below 2.5 mIU/L were related to clinical variables or treatment outcome in euthyroid patients with major depression.

Outpatients with major depression (n =166) were assigned to high-normal and low-normal TSH groups based on their basal TSH levels. The 2 groups were compared along clinical variables and treatment outcome.

The low-normal TSH group was significantly more depressed, as measured by Hamilton Depression Rating Scale scores, and had more anxiety symptoms and suicidal tendencies than the high-normal group. There was no difference in treatment response between the groups.

A comparison of low-normal and high-normal basal TSH groups with major depression revealed significant differences in severity and symptoms of depression but no difference in treatment outcome. These data are preliminary and require replication in a larger sample.