Abstract Body (Do not enter title and authors here): Description of Case:
A 53 year old female with past medical history of autoimmune thyroid disease post-thyroidectomy (not on levothyroxine for over one year), chronic lower extremity edema, generalized anxiety disorder, hysterectomy, and cholecystectomy, presented with 2 day history of progressive bilateral leg swelling and right lower extremity erythema. She reported worsening exertional dyspnea and orthopnea over several months. She denied chest pain, syncope, fever, chills, nausea, or diaphoresis. Initial labs were notable for anemia with a hemoglobin of 8.3, potassium 3.3, elevated TSH 38.21, with a low free T3 1.8 and low free T4 0.25, normal BNP 36 and elevated D-dimer 1.32. Chest X-ray showed cardiomegaly with mild perihilar pulmonary congestion. EKG showed normal sinus rhythm and nonspecific findings of an old anterior myocardial infarction. Transthoracic echocardiogram (TTE) revealed a large pericardial effusion with right atrial and right ventricular collapse, consistent with cardiac tamponade. Urgent pericardiocentesis was performed under echocardiographic and fluoroscopic guidance, and 500 mL of straw-colored pericardial fluid was aspirated. Post-procedural TTE confirmed complete resolution of the effusion and normalization of cardiac chamber function without evidence of residual tamponade physiology.
The pericardial fluid was sent for diagnostic analysis which was exudate. A pericardial drain was left in place and removed after 24 hours. Plan is for repeat TTE in 2 weeks.

Discussion:
Hypothyroidism is a known but rare cause of large pericardial effusions and tamponade. This case underscores that while pericardial effusion is a relatively common finding in hypothyroidism, progression to tamponade is rare due to the typically slow accumulation of fluid. However, delayed recognition or additional stressors can tip a patient into hemodynamic compromise. Clinicians should maintain a high index of suspicion for pericardial effusion in patients with long-standing or untreated hypothyroidism presenting with dyspnea or hemodynamic instability. Prompt echocardiographic evaluation and thyroid hormone replacement are essential for optimal outcomes.