Lithium: Thyroid effects and altered renal handling

Background: Lithium is frequently used in the treatment of bipolar affectiv e disorder, and is widely known to affect thyroid function, most commonly r esulting in hypothyroidism and goiter, Less well-known is the association b etween lithium therapy and hyperthyroidism and the potential for lithium to moderate the effects of thyroxine at a cellular level. Lithium excretion r elates principally to glomerular filtration rate and proximal tubule functi on. Thyroxine, through its effects on tubular function, alters lithium clea rance such that thyroid disease may cause retention of lithium and subseque nt toxicity. Case Reports: We report 2 cases with Lithium toxicity, both of whom were later found to be hyperthyroid, One patient developed thyroid st orm following dialysis to remove lithium, The other received antithyroid me dication early. Both suffered a protracted multifactorial delirium requirin g intensive inpatient care, Conclusion: In addition to altering thyroid fun ction, lithium therapy may mask the signs of hyperthyroidism by inducing ce llular unresponsiveness. In some lithium-treated patients with biochemical hyperthyroidism, early antithyroid treatment may be appropriate. Altered re nal tubular function induced by hyperthyroidism may result in retention of lithium and systemic toxicity. We propose induction of the proximal tubule sodium hydrogen antiporter as the relevant mechanism.