The aim of this study is to report a rare case of massive pericardial effusion as initial manifestation of hypothyroidism. A previously healthy 21-year-old female patient suddenly began presenting dyspnea at rest and lower limb edema. Routine laboratory tests performed at admission showed hypothyroidism (TSH 146.14 mUI/L) and echocardiography showed significant pericardial effusion. Therapy was instituted with levothyroxine, resulting in clinical improvement without pericardiocentesis. The patient was followed up for 1 year, with total remission of dyspnea and edema. However, she developed typical symptoms of hypothyroidism, and remained with asthenia, dyslipidemia, weight gain, and mild pericardial effusion at the end of one year, even with the optimization of the levothyroxine dose. This case highlights the need for early investigation of hypothyroidism in patients with pericardial effusion.
