MON-370 - The Silent Heart of Hypothyroidism: From Massive Pericardial Effusion to Delayed Cardiac Tamponade Requiring Pericardial Window

Introduction
Pericardial effusion is a known complication of multiple conditions, including thyroid disease. It is observed in up to 80% of severe hypothyroidism cases. Pathophysiology involves increased pericardial permeability and impaired lymphatic drainage, allowing fluid accumulation as the pericardium stretches. We present a rare case of a 37-year-old male with massive pericardial effusion secondary to undiagnosed hypothyroidism, later developing tamponade due to medication non-adherence. This case emphasizes the potentially life-threatening consequences of a common endocrine disorder.
Case presentation
A 37-year-old healthy male presented with one month of fatigue and bilateral leg swelling. Vitals were normal, with distant heart sounds and 2+ lower extremity edema on physical exam. ECG showed low-voltage QRS complexes. Labs revealed TSH >46 µIU/mL, FT4 < 0.5 ng/dL, and FT3 < 150 pg/dL. Imaging confirmed a large pericardial effusion without tamponade. He underwent pericardiocentesis with drainage of 2.5 L of fluid and started on intravenous thyroid hormone replacement. Once FT3 and FT4 became detectable, he was switched to oral levothyroxine and discharged with follow-up care but was lost to follow-up due to financial constraints.
One year later, he returned with worsening edema, dyspnea, and chest pain. He was hemodynamically unstable; myxedema and muffled heart sounds were noted. Labs showed similar findings to the first presentation, indicating uncontrolled hypothyroidism. TTE revealed a large pericardial effusion with tamponade physiology and right ventricular collapse. He received IV thyroid hormone and underwent a pericardial window after unsuccessful pericardiocentesis. Once stabilized, he was transitioned to oral levothyroxine 250 mcg daily and discharged with counseling on medication adherence and follow-up.
Discussion
The case highlights the importance of early recognition of hypothyroidism as an underlying cause of pericardial effusion and tamponade. This is particularly crucial in cases of unexplained effusion or when classic tamponade signs are absent. Thyroid hormone replacement alone can resolve effusions and, in some cases, avoid invasive procedures. However, when tamponade with hemodynamic instability is present, pericardiocentesis or surgery remains essential. Due to the lack of standardized guidelines, treatment should be individualized, and further research is needed to refine protocols. Long-term success requires patient education, adherence, and support to ensure continuity of care.

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