Association between Lithium and thyroid function: a retrospective study

IntroductionBipolar Disorder (BD) is associated with thyroid dysfunction, and literature on the clinical impact of Lithium on thyroid function in BD patients remains inconsistent. Thus, we aimed to systematically estimate the prevalence of thyroid dysfunction in Lithium treated BD patients, explore the clinical factors associated with the development of hypothyroidism and time to detection of thyroid dysfunction after Lithium initiation. MethodsA retrospective review of BD patients with a follow-up between Jan to Dec 2019 was conducted. Patients with no pre-existing thyroid dysfunction and at least six months of cumulative exposure to Lithium were included. For the included 444 patients, sociodemographic, clinical variables and laboratory assessment values were charted systematically. Patients with TSH > 5 mIU/L were classified as hypothyroid. Results27.7% (n=123) developed thyroid dysfunction; 27.3% (n=121) developed hypothyroidism after Lithium exposure. The median duration of detection of hypothyroidism was 33.6 months for females and 38.4 months for males, with no significant difference across genders (p=.52). A significantly higher proportion of females (49.5%) developed hypothyroidism as opposed to males (23.7%). Hypothyroid females differed significantly with respect to comorbid diabetes mellitus and hypertension; from euthyroid females. First-episode depression was associated with hypothyroidism in males. However, multivariate analyses did not detect any associations. DiscussionOne-fourth of Lithium-treated patients developed hypothyroidism. This risk was higher in female patients, with onset close to 33 months, indicating the need for closer monitoring for long durations. The impact of hypothyroidism on prognosis and response to treatment needs further exploration.