Low T₃ syndrome in psychiatric depression

Abstract

In euthyroid sick syndrome [non-thyroidal illness (NTI)], a number of investigators have described TSH and serum thyroid hormone abnormalities, low T₃, low T₃ and T₄, increased T₄, low TSH, etc. Those cases of NTI where there is only T₃ decrease [and normal serum T₄, free T₄ (FT₄), and TSH levels] are specifically referred to as low T₃ syndrome. However, the information in regard to low T₃ syndrome in psychiatric subjects who are clinically euthyroid and do not have any other systemic illness is scanty. In our facility, since thyroid function is routinely assessed in psychiatric patients at admission, this provided the opportunity to study low T₃ syndrome in a large group of psychiatric patients. Out of 250 subjects with major psychiatric depression, 6.4% exhibited low T₃ syndrome (mean serum T₃ concentration 0.94 nmol/l vs normal mean serum concentration of 1.77 nmol/l). The low T₃ levels could not be ascribed to malnutrition or any other illness and the metabolic parameters were all normal. Possible mechanisms contributing to low T₃ are discussed. The depression might constitute an illness having the same relation to low T₃ as found in the low T₃ syndrome previously described in euthyroid sick subjects. The present findings, besides describing low T₃ syndrome in psychiatric patients without systemic illnesses, suggest the possibility of subgrouping in clinical psychiatric depression which may have a broader clinical significance.