SUN-358 - Severe Hypothyroidism Presenting as Cardiac Tamponade: A Reversible but life-threatening Endocrine Emergency

Background: Severe hypothyroidism can lead to pericardial effusion through increased capillary permeability and impaired lymphatic drainage. While effusions are typically indolent, progression to cardiac tamponade is rare but life-threatening, requiring emergent intervention. Prompt recognition is critical, as thyroid hormone replacement is definitive therapy and prevents recurrence.

Case Presentation: A 61-year-old woman with longstanding uncontrolled hypothyroidism presented with progressive dyspnea. Her TSH had remained elevated for years due to reported adverse effects from levothyroxine, resulting in medication nonadherence. Laboratory evaluation revealed TSH 69.8 mIU/L and free T4 < 0.07 ng/dL. Echocardiography demonstrated a large pericardial effusion with right ventricular diastolic collapse, consistent with tamponade physiology.

The patient underwent an emergent subxiphoid pericardial window with drainage of 500 mL serous fluid, resulting in rapid symptomatic improvement. On postoperative day 1, the patient developed hypotension requiring fluid and norepinephrine support. Repeat echocardiography showed improvement in the effusion with residual pericardial thickening. Intravenous levothyroxine was initiated. By postoperative day 3, pericardial drain output had significantly decreased with hemodynamic improvement, allowing discontinuation of vasopressors and brief use of oral midodrine. By postoperative day 5, the patient was ambulating with resolution of respiratory symptoms. She was discharged on oral levothyroxine with strict counseling on adherence and outpatient endocrinology follow-up.

Discussion: Although pericardial effusion is a recognized complication of hypothyroidism, tamponade remains uncommon due to gradual fluid accumulation. This case highlights the importance of recognizing hypothyroidism as an underlying cause, particularly in patients with large effusions and unclear etiology. Definitive management requires both emergent drainage and prompt thyroid hormone replacement.

Conclusion: Cardiac tamponade is a rare but reversible manifestation of severe hypothyroidism. Early diagnosis and timely initiation of thyroid hormone replacement are essential to optimize outcomes and prevent recurrence.

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