EFFECTS OF LITHIUM TREATMENT ON HYPOTHALAMIC-PITUITARY-THYROID AXIS -A LONGITUDINAL-STUDY

Lithium carbonate, widely used in the treatment of bipolar patients, i s 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 thy roid function and absence of thyroid antibodies. Nine of the 12 patien ts were further studied on the 15th month, 5 of these 9 on the 18th mo nth and 4 of the last-mentioned 5 on the 24th month. The mean basal an d TRH-stimulated TSH values during lithium therapy were significantly higher as compared to those at the beginning of the treatment. More pa rticularly, during lithium therapy, a significant increase of basal TS H 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 imp airment of the hypothalamic-pituitary-thyroid (HPT) axis was transitor y in the majority of cases. Two patients developed a nodular goiter du ring the treatment. Plasma T3, T4, FT3 and FT4 levels did not change d uring the treatment. Thyroid antibodies remained undetectable. The con clusions of the study are twofold: 1) Subclinical hypothyroidism durin g 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 ri sk of a subsequent goiter.