Oral Levothyroxine Treatment in Lithium Intoxication- Induced Myxedema Coma: A Case Report

Lithium intoxication-induced myxedema coma, a rare but dangerous condition of severe hypothyroidism, can be easily misdiagnosed in patients without history of hypothyroidism. The objective of this case report is to describe a lithium-treated patient who presented to emergency department with obtundation and moderate hypothermia and was diagnosed with myxedema coma and lithium toxicity. A 64-year-old female presented to the emergency department with obtundation and hypothermia. The patient had the past history of stage-III chronic kidney disease, bipolar-type schizoaffective disorder, hypertension, and hyperlipidemia, and she had received long-term lithium therapy for the schizoaffective disorder. Bradycardia with hypotension developed after a few hours of admission and thyroid function revealed thyroid-stimulating hormone 53.1 nIU/mL and free T4 (FT4) 0.11 ng/dL, and the serum lithium level was 2.54 mmol/L. Therefore, diagnosis of lithium intoxication-induced myxedema coma was made, and the patient was managed with oral form of levothyroxine (LT4) (loading dose of 400 mcg followed by 100 mcg per day), intensive fluid therapy, empirical antibiotics, mechanical ventilation, and inotropic agents; lithium had been discontinued since admission. The patient weaned from the mechanical ventilation and inotropic support at day 4 of admission and by day 6, the patient's consciousness had fully recovered; on day 9, the serum lithium level was 0.37 mmol/L. The patient's FT4 recovered to the normal range (0.96 ng/dL) on day 15. In patients with no history of hypothyroidism or neck surgery and radiation therapy, lithium intoxication can be the single contributor to myxedema coma, which can be treated with oral form of LT4 as thyroid replacement therapy with instant and intensive supportive care. However, further study is needed to compare the outcomes of the patients with myxedema coma treated by oral and intravenous LT4.