Free-thyroxine index in psychotic and neurotic depression.

The mean free-thyroxine index value of a group of 25 psychotic depressive patients was found to be significantly lower than that of an age- and sex-matched group of 20 neurotic depressives (P less than 0.01). These findings support the view that psychotic and neurotic depression are differentiated not only with respect to their clinical expression, but also on account of their biological substrate. Comparison of free-thyroxine index values of each group of patients with a group of 240 euthyroid subjects hospitalized for various somatic illnesses revealed a lower mean free-thyroxine index value in the group of psychotic depressives (P less than 0.001). The neurotic depressives were not differentiated from the group of euthyroid subjects. The decreased thyroid activity in psychotic depression might be interpreted in the light of recent findings implicating catecholamines in both the release of hypothalamic hormones and the neurochemical mechanism of the affective disorders.