A 67-year-old woman was admitted with signs and symptoms of Graves
thyrotoxicosis. Biochemistry results were as follows: TSH was undetectable; FT4 was >6.99 ng/dL (0.7-1.8); FT3 was 18 pg/mL (3-5); TSI was 658% (0-139). Thyroid uptake and scan showed diffusely increased tracer uptake in the thyroid gland. The patient was started on
methimazole 40 mg BID, but her LFTs elevated precipitously with features of
fulminant hepatitis.
Methimazole was determined to be the cause and was stopped. After weighing pros and cons,
lithium was initiated to treat her persistent
thyrotoxicosis.
Lithium 300 mg was given daily with a goal to maintain between 0.4 and 0.6. High dose
Hydrocortisone and
propranolol were also administered concomitantly. Free
thyroid hormone levels decreased and the patient reached a biochemical and clinical euthyroid state in about 8 days. Though definitive RAI was planned, the patient has been maintained on
lithium for more than a month to control her
hyperthyroidism. Trial removal of
lithium results in reemergence of
thyrotoxicosis within 24 hours. Patient was maintained on low dose
lithium treatment with
lithium level just below therapeutic range which was sufficient to maintain euthyroid state for more than a month. There were no signs of
lithium toxicity within this time period. Conclusion.
Lithium has a unique physiologic profile and can be used to treat
thyrotoxicosis when thionamides cannot be used while awaiting elective radioablation.
Lithium levels need to be monitored; however, levels even at subtherapeutic range may be sufficient to treat
thyrotoxicosis.