Lithium therapy duration not linked to thyroid effects

By Eleanor McDermid, Senior medwireNews Reporter

The risk of altered thyroid function does not increase with duration of lithium treatment in patients with bipolar disorder, research suggests.

Instead, female gender was the main factor associated with changes in thyroid function, in line with most previous studies, say Janusz Rybakowski (Poznan University of Medical Sciences, Poland) and study co-authors.

Their study, which involved 66 bipolar disorder patients who had been taking lithium for up to 44 years, found no differences in thyroid function between patients who had taken the medication for 10–20 years and those who had taken it for longer.

“It is likely that lithium-induced thyroid dysfunction requiring levothyroxine replacement may manifest itself during the early years of lithium treatment”, they therefore suggest in Bipolar Disorders.

After excluding seven women who were taking levothyroxine replacement therapy, the team found no overall differences in levels of thyroid-stimulating hormone (TSH), free triiodothyronine (fT4) and free thyroxine (fT3) between the 21 men and 38 women in the study.

However, three women had abnormally high TSH levels (≥4.9 μIU/mL), one had abnormally low fT4 (≤0.7 ng/dL) and one had abnormally low fT3 (≤1.71 pg/mL). None of the men had abnormal thyroid hormone levels unless the TSH cutoff was reduced to 3.0 μIU/mL, in which case four men and five women had elevated levels.

Anti-thyroid antibodies were common among the patients, with 45% having antibodies against thyroid peroxidase and 65% having antibodies against thyroglobulin. Again, antibody levels did not differ according to the duration of lithium treatment, but thyroglobulin antibody levels did significantly correlate with the duration of illness.

The researchers say this fits with a previous study that showed similar levels of thyroid antibodies in elderly patients taking and not taking lithium.

“Therefore, in view of a significant correlation between anti-[thyroglobulin] antibodies and duration of illness, it can be speculated that these immune disturbances may be connected with the illness itself and not directly with lithium therapy”, they conclude.

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