SAT475 Levothyroxine and Liothyronine Treated Myxedema Coma with Irreversible Cardiopulmonary Failure: A Rare Phenomenon

Disclosure: T. Menon: None. Y. Xie: None. A. Wang: None. Introduction: We describe a case of myxedema coma associated with irreversible cardiogenic shock and the challenges in optimal management. Case Presentation: A previously healthy 23-year-old man with a history of untreated hypothyroidism (TSH 100 uIU/mL six months prior) presented to the hospital for abdominal pain, shortness of breath, and cough. He soon had two cardiac arrests with successful resuscitation and was stabilized via mechanical ventilation and vasopressors. Physical exam showed peripheral and facial edema with mild jaundice. Laboratory results showed elevated creatinine 1.73 (0.5-1.30 mg/dL), AST 440 (10-40 U/L), ALT 353 (10-45 U/L), and total bilirubin 3.6 (0.2-1.2 mg/dL). Thyroid function tests showed TSH 857 (0.27-4.20 uIU/mL), FT4 <0.1 (0.9-1.8 ng/dL), and TT3 < 20 (80-200 ng/dL), and negative thyroglobulin and TPO antibodies. A thyroid ultrasound showed a small thyroid gland. Echocardiogram revealed severe bi-ventricular failure, with an ejection fraction of 10-15%, dilated chambers, pulmonary hypertension, and moderate pericardial effusion. The patient was initiated on VA-ECMO and treated medically for cardiogenic shock. Myxedema coma treatment was started with IV levothyroxine (LT4) 400 mcg, IV Liothyronine (LT3) 10 mcg, and IV hydrocortisone 100 mg every eight hours. The patient subsequently received IV LT4 100 mcg daily and IV LT3 10-30 mcg daily based on levels of daily FT4 and TT3. Hydrocortisone was tapered down as free cortisol levels prior to steroid administration were elevated at 4.6 (0.2-1.8 ug/dL). Despite significant improvements in TSH values (from 857 to 67 uIU/L), FT4 (from <0.1 to 1.2 ng/dL), and TT3 (from < 20 to 60 ng/dL), the patient’s cardiac function did not improve and he underwent successful orthotopic heart transplantation two weeks after initial presentation. A cardiac biopsy demonstrated cardiomegaly with left ventricular hypertrophy, subendocardial fibrosis, and patent arteries, without other etiologies of heart failure. The patient recovered and was discharged on oral LT4 137 mcg daily, LT3 5 mcg twice daily, and prednisone per cardiac transplantation protocol. Discussion: Several cases describe myxedema coma with reversible heart failure in 4 to 5 days with appropriate hypothyroidism treatment. This case, however, describes irreversible cardiomyopathy despite optimal medical therapy, eventually requiring heart transplantation. Because the cardiac myocyte is dependent on plasma T3 due to lack of intracellular deiodinase, T3 administration may improve cardiac function in myxedema coma induced heart failure. Consensus regarding the use, optimal dose, and duration of LT3 in these situations requires further investigation. Conclusion: We report an unusual case of irreversible cardiomyopathy due to myxedema coma in a young, healthy patient, highlighting the need for rapid correction of hypothyroidism with both IV LT4 and LT3. Presentation Date: Saturday, June 17, 2023