Hypothyroidism in patients with bipolar I disorder treated primarily with lithium

Aims - This study evaluated the frequency and clinical significance of abnormal Thyroid Stimulating Hormone (TSH) and Free Thyroxine Index (FTI) in patients with bipolar I disorder treated primarily with lithium. Method - We evaluated the medical records of 143 participants in the Pittsburgh study of Maintenance Therapies in Bipolar Disorder who did not have a thyroid abnormality at entry. Results - Thirty-six percent of the 143 patients developed abnormal TSH and/or FTI values. Thirty-eight percent of the 135 patients who received lithium developed abnormal TSH and/or FTI, spent significantly longer time in the acute treatment phase (t = -3.6, df = 133, p = .0004), and had significantly higher mean Hamilton Scale for Depression scores over the course of the maintenance phase (t = -2.3, df = 71.6, p = .03). Time on lithium and development of abnormal TSH and/or FTI were positively correlated (r = .25, p = .004). Conclusions - Thyroid dysfunction can be frequent in patients exposed to lithium treatment for bipolar I disorder; it also appears to be correlated with a slower response to acute treatment, and may be related to poorer quality of long-term remission. A prospective study is needed to confirm our findings and determine whether more aggressive thyroid replacement can optimize thyroid function to facilitate clinical recovery.