Thyroid dysfunction and lithium maintenance therapy in Bahraini out-patients

ABSTRACT

The definition, prevalence, etiology and clinical significance of lithium-associated subclinical hypothyroidism are uncertain. To determine the prevalence and risk factors for subclinical hypothyroidism among Bahraini patients on long-term lithium therapy. A retrospective study was conducted in all patients attending the out-patient clinic at the Bahrain Psychiatric Hospital who were diagnosed according to ICD-10 criteria as bipolar affective disorder, schizoaffective disorder or resistant depression, and were receiving maintenance lithium therapy for one year or longer. The age, gender, dosage of lithium, duration of lithium therapy, and duration of therapy until the development of thyroid dysfunction if it occurred, was the variables analyzed. Thyroid stimulating hormone [TSH; reference range 0.25 - 4.5 mU/L] and free thyroxine [T[4]; reference range 6.0 - 24.5 pmol/L] in serum were measured. In a sample of 32 patients 12 were female and 20 were male with a mean [ +/- SD] age 40.41 +/- 9.13 years. The age at onset of illness was 22.78 +/- 7.4 years, and lithium therapy was initiated at the age of 30.53 +/- 8.85 years. The dosage of lithium [mean +/- SD] was 812.5 +/- 282.6 mgs/day administered for a duration of 10.72 +/- 7.02 years. The level of TSH and thyroxine [mean +/- SD] were 3.45 +/- 3.1 mU/L and 15.5 +/- 3.14 pmol/L, respectively. Seven patients [21.9%] were considered to have had a subclinical hypothyroidism judged by a TSH level of >/= 4.5 mU/L; of these four were females. None of the patients had overt hypothyroidism or hyperthyroidism. Subclinical hypothyroidism is a relatively common adverse effect associated with lithium maintenance therapy. The duration of lithium therapy and female gender are important predictive factors. It is important to screen patients on lithium therapy for thyroid dysfunction for early detection and management