Cardiac Tamponade: A Late and Rare Finding of Hypothyroidism.

"Myxedema heart" is a rare syndrome that results from severe untreated hypothyroidism. It is characterized by relative bradycardia, low-voltage electrocardiogram (EKG), cardiomyopathy, and pericardial effusion. Here, we present a case of cardiac tamponade in untreated hypothyroidism. A 49-year-old male with no prior medical or psychiatric history presented to the Emergency Department for cognitive slowing, weakness, and inappropriate behavior for several weeks. Vital signs were significant for bradycardia with normal blood pressure. Examination revealed that the patient was disheveled and alert but forgetful with slow speech, along with ataxia and muscle wasting. The EKG showed low-voltage sinus bradycardia. Laboratory workup was notable for an elevated thyroid-stimulating hormone (TSH) level of more than 100 mcIU/mL, with low free T4 and T3. Anti-thyroid peroxidase (TPO) and thyroglobulin antibodies were elevated, confirming a diagnosis of Hashimoto's thyroiditis. Treatment with intravenous levothyroxine, triiodothyronine, and hydrocortisone was started. An echocardiogram revealed a large circumferential pericardial effusion with evidence of tamponade. A pericardial drain was placed, and it drained 980 mL of sanguineous fluid. Serial echocardiograms showed a stable posterior effusion with no recurrence of the anterior pericardial effusion. Gradually, the patient's mentation, hemodynamics, and electrolyte levels improved. He was discharged on oral levothyroxine. TSH values showed sequential improvement. A large pericardial effusion with tamponade is a rare, life-threatening complication of untreated hypothyroidism. Clinicians must promptly identify myxedema and replace thyroid hormone to prevent the progression of pericardial effusion to tamponade and reverse its pathophysiology, maintaining a high level of suspicion in those at risk of poor healthcare access or inadequate health literacy.