Large Pericardial Effusion Secondary to Generalized Myxedema from Undiagnosed Hashimoto's Thyroiditis.

BACKGROUND Pericardial effusions are considered to be present when accumulated fluid within the pericardial sac exceeds the small amount that is normally present, causing impairment in the diastolic filling of the right heart. This case demonstrates an uncommon presentation of a large pericardial effusion by showing its relationship to myxedema in a patient with untreated hypothyroidism. CASE REPORT A 42-year-old man with a past medical history of hypertension, diabetes mellitus, and opioid abuse presented to the emergency department due to altered mental status, for which he received Narcan without resolution of symptoms. Computed tomography (CT) of the brain was without any acute intracranial abnormalities to explain the patient's altered mental status. CT chest reported a pericardial effusion, with a subsequent transthoracic echocardiogram (TTE) showing a moderate-to-large circumferential effusion without right atrial/ventricular collapse and no cardiac tamponade physiology. On further investigation, he was found to have severe hypothyroidism with elevated thyroid peroxidase antibodies. Endocrinology was consulted to start IV levothyroxine and liothyronine to treat autoimmune Hashimoto's thyroiditis. Subsequent TTE after starting hypothyroidism treatment showed an ejection fraction (EF) of 45-50% with mildly reduced left ventricular systolic function and moderate-to-large pericardial effusion, with no evidence of tamponade physiology. After treatment of hypothyroidism, the thyroid panel, EF, and pericardial effusion improved significantly. CONCLUSIONS This case illustrates the potential for suffering a large pericardial effusion secondary to generalized myxedema in a patient with severe hypothyroidism from undiagnosed Hashimoto's thyroiditis. It is important to recognize this condition for appropriate therapy and prevention of worsening cardiac conditions.