MON-440 Combination of Oral Levothyroxine and Liothyronine as Treatment for Severe Hypothyroidism With Cardiac Tamponade: A Case Report

Abstract Disclosure: A.M. Agurcia: None. A. Segovia-Palomo: None. M.A. Alvarez Castillo: None. F.C. Guillen Oviedo: None. C.E. Del Muro Baeza: None. INTRODUCTION: A decrease in the production of thyroid hormones is a key characteristic of the clinical condition known as hypothyroidism. Pleural and pericardial effusions are less common clinical manifestations resulting from increased vascular permeability to albumin, the extravasation of mucopolysaccharides, and inappropriate secretion of antidiuretic hormone. Pericardial effusion with tamponade is an even rarer complication of severe, uncontrolled hypothyroidism. CLINICAL CASE: A 67-year-old woman with a history of autoimmune primary hypothyroidism, type 2 diabetes, and arterial hypertension presented to the emergency department with dyspnea. The patient began treatment with levothyroxine three years ago; however, she had poor adherence. The physical examination showed an absence of the vesicular murmur in the left hemithorax, indicating a significant pleural effusion. The electrocardiogram revealed sinus bradycardia with low voltage, with no arrhythmias or signs of acute ischemia. 1.1 L of pleural fluid was drained, and the cytological analysis indicated transudate. A bedside echocardiogram was performed, revealing pericardial effusion. In light of this finding, a pericardial window was established, yielding serosanguinous fluid that showed negative cytology for malignancy and negative cultures, effectively ruling out infection. The thyroid function panel showed an elevated TSH of 72.3 mIU/L and low free T4 of 0.02 ng/dL (0.58-1.64 ng/dL). Given the severe uncontrolled hypothyroidism as a suggestive cause of pericardial effusion, an endocrinology consultation was requested, and treatment with oral levothyroxine in doses for 3 days (300 mcg/day) was started, with significant clinical improvement. TSH decreased to 55 mIU/L, and free T4 increased to 0.63 ng/dL. Control echocardiogram ruled out alteration of ventricular contraction. Subsequent treatment was started with levothyroxine 100 mcg and liothyronine 2.5 mcg. After 72 hours of this management, supplemental oxygen was discontinued, and the patient was discharged with a resolution of symptoms. CONCLUSION: The severity and duration of thyroid deficiency determine the magnitude of fluid accumulation. Treatment with levothyroxine reverses this condition and prevents hemodynamic complications. At the same time, liothyronine is useful when the conversion of T4 to T3 is decreased, so this addition can be considered the treatment of choice in patients without hemodynamic compromise. In cases of cardiac tamponade, pericardiocentesis is key. Rapid hormonal treatment improves the prognosis and accelerates recovery, especially with combined therapy. Presentation: Monday, July 14, 2025