A total of 4678 patients had lithium levels available for analysis; they were compared to the 689,228 patients who did not. After accounting for other variables that could have an impact on the results such as age, sex, and the presence of diabetes, the use of lithium was associated with an increased risk of hypothyroidism, but not of hyperthyroidism. Most problems appeared to occur early during the treatment and among those who had higher blood lithium levels. Younger women (<60 years old) were the most commonly affected.
The strength of this study is the use of a large database form a single health system going back 20 years. The weakness of the study is that there were no available data regarding dose, compliance or the use of other medications that could also independently affect thyroid function.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The conclusion of this study is that the use of lithium is associated with an increased risk of developing hypothyroidism, especially in younger women. This is important for patients because mood disorders are relatively common and lithium is still widely used to treat them. The authors suggest that patients, especially young women, should be monitored for thyroid function problems when they are managed with lithium. Although this is not a recommendation stated in the current guidelines of the American Thyroid Association, consideration might be given to certain patients who are at a higher risk, such as those who have a strong family history or who have a goiter prior to start treatment.
— Jessie Block-Galarza, MD
ATA THYROID BROCHURE LINKS
Thyroid Function Tests: http://www.thyroid.org/thyroid-function-tests/