Severe Menorrhagia as the Initial Presentation of Myxedema Coma With Pericardial Effusion.

Myxedema coma is a rare but serious complication of severe hypothyroidism, often presenting without coma, complicating diagnosis. Cardiovascular and hematologic abnormalities can predominate, including pericardial effusion and bleeding diathesis. We describe a 38-year-old woman with no thyroid history who presented with significant menorrhagia and acute anemia. She had fatigue, cold intolerance, and intermittent bradycardia but no hypothermia or altered mental status. Evaluation revealed a prolonged activated partial thromboplastin time and a large pericardial effusion with early tamponade, requiring pericardiocentesis. Thyroid testing showed profound hypothyroidism. Her presentation suggested myxedema coma despite preserved consciousness. She was treated with intravenous levothyroxine, hydrocortisone, red blood cell transfusion, and progestin therapy, resulting in complete resolution of the effusion and stabilization of hemoglobin. She remained asymptomatic on oral levothyroxine at 2-month follow-up. This case highlights an unusual presentation of new-onset hypothyroidism manifesting as menorrhagia with coagulopathy and pericardial effusion. The reversible nature of both the hematologic and cardiovascular findings underscores the importance of early recognition and treatment. Clinicians should consider thyroid dysfunction in unexplained heavy menstrual bleeding or severe anemia, particularly when systemic features suggest endocrine involvement.