Serum Thyrotropin and Thyroxine Concentrations in Patients Receiving Lithium Carbonate

Abstract

To determine the incidence of thyroid dysfunction in patients receiving therapy with lithium carbonate, serial determinations of serum thyrotropin (TSH) and thyroxine (T4) concentrations were made in 255 patients receiving lithium. The patients were followed for an average of 8 months and the longest period of lithium treatment was 65 months. The mean peak TSH level in the lithium treated patients was 3 times higher than in the control groups; elevated (>8 μU/ml) TSH levels occurred in 29.8% of the patients (76) at some time during treatment. At the time of final testing, 14.1% (36) of the patients had elevated serum TSH levels. The mean peak and final thyroxine concentrations in the lithium treated patients were only slightly lower than those in the control groups. In 15 patients whose final serum TSH levels were over 20 μU/ml, the mean thyroxine concentration was 2.9 μg/100 ml. A significantly higher incidence of positive anti-thyroglobulin antibody tests was found in these patients. Most were considered to have significant hypothyroidism and received thyroid treatment. In 27 patients pretreatment data were available. In these patients mean TSH levels significantly increased within the first 3 months of treatment and remained above pretreatment levels thereafter. Serum thyroxine levels did not change significantly. These results indicate that anti-thyroid effects of lithium, as manifested by elevated serum TSH levels, can be detected at some time in almost one-third of patients receiving it. With continued treatment, the anti-thyroid effect of lithium may either be lessened, with return of TSH levels to normal, or progress to the development of frank hypothyroidism.