Differences in hypothyroidism between lithium-free and -treated patients with bipolar disorders

The majority of the previous studies of thyroid abnormalities in bipolar patients was conducted in populations containing various proportions of lithium-treated subjects. In the present study, we sought to determine whether there exist differences in hypothyroid profile between lithium-free and -treated bipolar patients. Bipolar patients never treated with lithium and carbamazepine (n=78) and those currently in lithium therapy (n=53) were included in this study. Serum concentrations of total thyroxine (T(4)), total triiodothyronine (T(3)), and thyroid-stimulating hormone (TSH) were compared between lithium-free and -treated patients. The rate of hypothyroidism in lithium-free patients was significantly lower than those treated with lithium (6.3%-10.8% vs. 28.0%-32.1%). Significant changes in the three thyroid indices indicative of hypothyroidism were consistently associated with longer illness duration in lithium-free manic patients, but with greater severity of mania and more mood episodes in their lithium-treated counterparts. In lithium-free depressed patients, more episodes were associated with lower T(4) levels; whereas in their lithium-treated counterparts, longer illness duration was associated with higher TSH levels and females with lower T(3) levels. These results suggest that bipolar patients with and without lithium exposure differ in prevalence and association of hypothyroidism and may have different response to thyroid hormone therapy.