Effects of lithium treatment on hypothalamic-pituitary-thyroid axis: a longitudinal study

Lithium carbonate, widely used in the treatment of bipolar patients, is well known to induce thyroid alterations. In this longitudinal study the thyroid function was investigated during lithium treatment over a period of 12 months in 12 euthymic bipolar patients with a normal thyroid function and absence of thyroid antibodies. Nine of the 12 patients were further studied on the 15th month, 5 of these 9 on the 18th month and 4 of the last-mentioned 5 on the 24th month. The mean basal and TRH-stimulated TSH values during lithium therapy were significantly higher as compared to those at the beginning of the treatment. More particularly, during lithium therapy, a significant increase of basal TSH over the normal range was found in 10 out of the 12 patients. A rise of TRH-stimulated TSH was found in 11 out of the 12 patients. The impairment of the hypothalamic-pituitary-thyroid (HPT) axis was transitory in the majority of cases. Two patients developed a nodular goiter during the treatment. Plasma T3, T4, FT3 and FT4 levels did not change during the treatment. Thyroid antibodies remained undetectable. The conclusions of the study are twofold: 1) Subclinical hypothyroidism during lithium therapy is much more frequent than previous cross-sectional studies suggest; 2) Thyroxine replacement in lithium-treated patients is advisable in order to prevent subclinical hypothyroidism and the risk of a subsequent goiter.