Thyroid function and psychiatric morbidity in patients with manic disorderreceiving lithium therapy

Euthyroid hyperthyroxinemia as a result of a transient increase in thyroid- stimulating hormone (TSH) levels may contribute to the development of manic disorder. Lithium has a potent short-term antithyroidal effect that may ac count for its antimanic action. The thyroid function and psychiatric morbid ity of 46 adult patients with manic disorder were assessed prospectively be fore and 1 and 6 months-after Lithium treatment. At baseline, the free thyr oxine level (FT4, 16.23 +/- 3.11 pmol/L) was at the high end of the normal range, whereas the free triiodothyronine (FT3, 4.24 +/- 0.65 pmol/L) and TS H (1.47 +/- 0.73 mIU/L) levels mere within the normal range. AU patients me re clinically euthyroid, but five of them (11%) had elevated FT4 levels. Ba seline FT3 and FT4 levels mere positively correlated with past psychiatric morbidity. The FT4 level at baseline and after 1 month of treatment mas pos itively correlated with scores on the Brief Psychiatric Rating Scale (p < 0 .02) and negatively correlated with scores on the Global Assessment Scale ( p < 0.005). During the first month of treatment, the reduction of FT3 and F T4 levels was significantly correlated with a decrease in psychiatric sympt oms. By 6 months, the FT3 level was no longer significantly different from that at the baseline, but FT4 levels remained significantly lower. The TSH level increased progressively from baseline to 6 months. Multilevel models showed that FT4 and serum lithium levels mere positively and negatively ass ociated with psychiatric symptoms, respectively. The findings of the study lend support to the notion that euthyroid hyperthyroxinemia contributes to acute mania and suggest that Lithium's short-term antimanic action may be m ediated by its antithyroid effect.