Lithium-associated clinical hypothyroidism. Prevalence and risk factors.

BACKGROUND: Rates of, and risk factors for, lithium-associated clinical hypothyroidism are uncertain. AIMS: To determine prevalence of and risk factors for clinical hypothyroidism in patients treated with lithium carbonate.
METHOD: Retrospective case-note review of 718 patients who had undergone serum lithium estimation during a 15-month period. Patients on thyroxine had a more detailed review.
RESULTS: The prevalence of clinical hypothyroidism during lithium treatment was 10.4%. The main risk factor was female gender (women 14% v. men 4.5%). Women were at highest risk during the first two years of lithium treatment, and women starting lithium aged 40-59 years had the greatest prevalence (> 20%). No equivalent risk factors emerged in men, although, like women, their prevalence of hypothyroidism was substantially higher than community rates.
CONCLUSIONS: The high rates of clinical hypothyroidism identified may call for a review of the drug information given to women, particularly to those starting lithium in middle age. Consideration should be given to screening for thyroid antibodies before treatment in high-risk cases. Monitoring of thyroid function should take into account gender, age and stage of lithium treatment.