MON-439 Hypothyroidism-Related Pericardial Effusion: Challenges and Consequences of Medication Non-adherence

Abstract Disclosure: A. Ghimire: None. E. Shrestha: None. S. Albert: None. Hypothyroidism-related pericardial effusion accumulates slowly and rarely causes cardiac tamponade. We present a case of hypothyroidism resulting in recurrent pericardial effusions with impending cardiac tamponade. Prolonged undertreated hypothyroidism due to medication non-adherence contributed to life-threatening cardiac dysfunction. A 52-year-old woman with a history of Graves' disease, treated with radioactive iodine ablation 14 years previously with subsequent hypothyroidism presented with constant chest/back pain and dyspnea on exertion. She had documented hypothyroidism for greater than one year and was not taking her thyroid or cardiovascular medications during that time. On x-ray evaluation, she was found to have a large pericardial effusion, which was confirmed by an echocardiogram. The patient was vitally stable. TSH was 115uIU/ ml, and free T4 <0.1ng/dl. The patient was repeatedly encouraged to take her thyroid hormone supplements. She was re-admitted several times with similar presentations. Echocardiograms on each admission showed large pericardial effusions with features suggestive of tamponade physiology (right ventricular diastolic collapse). Pericardiocentesis was performed due to impending cardiac tamponade, removing 1.5 to 2.2L of pericardial fluid during each episode. Pericardial windows were performed twice. The work-up for recurrent pericardial effusions showed that the pericardial fluid analysis and culture were negative for bacterial, tubercular and fungal infections. Cytology was negative for malignancy. Serum Quantiferon-TB and tests for autoimmune diseases were negative. Pericardial biopsy showed mesothelial-lined fibrous tissue without further histopathologic abnormalities. TSH levels were persistently elevated on each admission and were in the range of 43 uIU/ml -115uIU/mL and free T4 <0.1ng/dl to 0.7ng/dl. Thyroid hormone replacement was started at levothyroxine 50 mcg and increased incrementally to 112mcg orally daily with improvement in TSH to 3.7uIU/mL and free T4 of 0.9ng/dL. Symptomatic improvement correlated with thyroid function normalization for the first time in years. Upon discharge repeated echocardiograms continued to show effusions with pericardial sac dilation and she is scheduled for partial pericardiectomy. Conclusion: This case emphasizes the severity of longstanding untreated hypothyroidism and the critical role of medication adherence in managing hypothyroidism. While hypothyroidism-related pericardial effusion is typically reversible with thyroid hormone replacement, the inability of this patient to take medications resulted in recurrent effusion with impending cardiac tamponade and the need for invasive interventions. It underscores the need for vigilant assessment of hypothyroid management to prevent life-threatening complications. Presentation: Monday, July 14, 2025