SUN-268 - Severe Hypothyroidism Presenting with Massive Pericardial Effusion and Impending Cardiac Tamponade: A Rare but Critical Manifestation

Case presentation and findings:
A 69-year-old male with a past medical history of laryngeal lymphoma of the vocal cord, status post radiation one year prior and currently in remission, presented with progressively worsening dyspnea over one month, associated with orthopnea, bilateral lower extremity edema, weight gain, and fatigue. He was hemodynamically stable on presentation, with relatively low blood pressure. Physical examination revealed muffled heart sounds and 3+ lower extremity edema. Chest X-ray showed bilateral pleural effusions and cardiomegaly. An echocardiogram demonstrated a large pericardial effusion with evidence of cardiac tamponade, including diastolic right ventricular collapse.
The patient was managed in the critical care unit, where he underwent placement of a subxiphoid pericardial window for cardiac tamponade, along with bilateral chest tube placement for pleural effusions. A total of 600 cc of serous fluid was drained from the pericardial space. Additionally, 1.3 L of serous fluid was drained from the right pleural space and 1.6 L from the left pleural space. No blood pressure changes were noted during the procedure. Fluid samples were sent for analysis.

A CT scan of the chest, abdomen, and pelvis with contrast showed multiple bulky lymphadenopathies in the chest, abdomen, and pelvis, consistent with lymphoma. Pericardial fluid analysis revealed an exudative effusion while cytopathology was unremarkable.
Laboratory investigation showed elevated TSH of 75.100 uIU/ml, along with low T4 of 0.29 ng/dl and low total T3 of 0.41ng/ml. The patient was started on levothyroxine and was followed up in the endocrinology clinic.

Results/Follow-up:
At one month's follow up visit, the patient reported significant improvement in shortness of breath. His TSH was back to normal and the patient was doing well clinically.This findings suggested that his pleural and pericardial effusions were likely secondary to uncontrolled and undiagnosed hypothyroidism.

Conclusion:
Hypothyroidism-induced pericardial effusion progressing to tamponade is a rare but entirely reversible complication of untreated disease. In patients with prior head and neck radiation such as this individual treated for vocal cord lymphoma thyroid dysfunction should be considered early in the evaluation of unexplained pericardial or pleural effusions, even when malignancy is a leading concern on imaging. Because the condition is readily treatable, a simple TSH level can be diagnostic and life saving. Once hypothyroidism is identified, prompt initiation of levothyroxine and achievement of euthyroidism are essential to prevent recurrence of pericardial effusion or tamponade. This case serves as a reminder that, despite a complex oncologic history, the most straightforward endocrine explanation may be the correct one.

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