RESUMO
A 70-year-old woman was hospitalized for diarrhea, vomiting, loss of appetite, fatigue, and dyspnea on exertion for the past 3 weeks and treated with intravenous fluid for dehydration. She was receiving prednisolone for polymyositis. She did not have a history of thyroid disease. On day 4 of hospitalization, the patient was diagnosed with congestive heart failure and tachycardiac atrial fibrillation, and treatment with a diuretic agent was initiated. On day 7 of hospitalization, a clinical laboratory evaluation revealed that the level of free thyroxine was 9.95 ng/dL, free triiodothyronine was >30 pg/mL, and thyroid-stimulating hormone was <0.01 µU/mL, and the patient was initially diagnosed with thyrotoxicosis because of Graves' disease. She showed restlessness and had a fever of 39 °C, tachycardia of ≥140 beats/min, pulmonary edema, and frequent diarrhea, all of which were consistent with the symptoms of thyroid storm. Her general condition gradually improved with comprehensive treatment of thyroid storm comprising thiamazole, potassium iodide, hydrocortisone, and landiolol. A reassessment revealed that the patient had already had thyrotoxicosis and thyroid storm on admission. Thyroid storm is a potentially fatal disease that must be urgently addressed; however, its symptoms are difficult to distinguish from those caused by other diseases. Furthermore, elderly individuals may not exhibit typical symptoms of thyroid storm, so the diagnosis is difficult. In this case, the diagnosis was delayed because of the absence of typical symptoms of thyroid storm and the influence of a pre-existing medical condition and medication.