A Rare Case of Moderate Pericardial Effusion Uncovering Severe Hypothyroidism.

Severe hypothyroidism can manifest with various cardiovascular complications, including bradycardia, diastolic dysfunction, and, less commonly, pericardial effusion, due to thyroid hormone's regulatory effects on cardiac function. While small pericardial effusions may be seen in clinical practice, large effusions and tamponade are rare. We present a case of a 64-year-old female patient with obesity who was initially admitted for bilateral lower extremity cellulitis. During her hospitalization, clinical signs such as lethargy, puffy facies, and slow speech raised concern for hypothyroidism, prompting thyroid function testing, which revealed severe hypothyroidism (thyroid-stimulating hormone 58.3 mIU/L, free T4 0.51 ng/dL). A transthoracic echocardiogram, obtained as part of further evaluation, demonstrated a moderate circumferential pericardial effusion without tamponade physiology. She was managed conservatively with oral levothyroxine, and cardiology advised against pericardiocentesis due to hemodynamic stability. Pericardial effusion in hypothyroidism typically resolves with hormone-replacement therapy. This case underscores the importance of considering hypothyroidism in patients with nonspecific systemic symptoms and highlights its potential to cause clinically significant but reversible cardiovascular complications.