RESUMEN
Background: Graves' disease results in various clinical cardio-pulmonary manifestations such as tachycardia, atrial fibrillation, and pulmonary edema. Clinical Case: A 62-year-old woman presented with palpitations and dyspnea. Laboratory and radiologic examination revealed markedly elevated free T4 (4.79 ng/dL), T3 (4.42 ng/mL), lowered TSH (0.01 uIU/mL), atrial fibrillation and multifocal lung haziness. She was initially diagnosed with atrial fibrillation with pulmonary edema, which subsequently changed to pulmonary alveolar proteinosis by further evaluations such as computed tomography and bronchoscopic biopsy. Conclusion: Pulmonary alveolar proteinosis is a rare lung disease. Clinicians should carefully assess lung lesions in thyrotoxicosis patients as they can be easily mistaken for pulmonary edema in clinical practice.