Thyroid function was investigated in 100 manic-depressive patients.
Goiter was more common in patients treated with lithium for 1-5 years (44%)
or more than 10 years (50%) than in patients who never received lithium
(16%). Smoking contributed significantly to thyroid size and goiter. In
nonsmoking patients, ultrasonically determined thyroid volume was
significantly related to treatment duration. The mechanism behind this
increased thyroid volume is unclear, as most patients had normal serum
thyrotropin levels and no thyroid autoimmunity. Subclinical or overt
hypothyroidism was found in 4% and 21% of patients treated for 1-5 and more
than 10 years, respectively. Since few hypothyroid patients had
autoimmunity or goiter, lithium may affect the thyroid gland directly.