CARDIAC TAMPONADE DUE TO SEVERE MYXEDEMA. J. Blonsky 1 , V. Shivaswamy 1 , K. Hoskison 1 , R. Sekhar 1 , D. Perry 1 ; 1 University of Oklahoma, Tulsa, OK (Tracking  ID #75122) LEARNING OBJECTIVES: Recognize hypothyroidism as cause for cardiac tamponade. Diagnosis of cardiac tamponade secondary to hypothyroidism. Treatment of cardiac tamponade caused by severe tamponade. CASE INFORMATION: We report a 53-year-old male with an enlarging right testicle, progressive dyspnea, severe dependent edema, and cold intolerance. Physical examination revealed faint heart sounds, ascites, ankle jerks with delayed relaxation, and an enlargement of the right scrotum consistent with a hydrocele, and a clinical diagnosis of cardiac effusion with tamponade was entertained. Further evaluations revealed low voltage complexes on the EKG, and marked cardiomegaly on a Chest Roentgenogram with bilateral pleural effusions. An echocardiogram showed a large pericardial effusion with signs of early tamponade, and a pericardial paracentesis drained 1400ml of exudate. Pericardiocentesis led to significant clinical improvement. To confirm a unifying diagnosis thyroid functions were diagnosed of profound hypothyroidism with a TSH of 52.5 iu/ml. The patient responded well to thyroid hormone replacement therapy, and demonstrated continued recovery at clinic follow-up visits. The scrotal swelling was confirmed as a hydrocele by ultrasound. Hypothyroid effusions involving the pleural, pericardial, and peritoneal cavities have been described, but uncommon clinically. Pericardial effusions tend to be large, and asymptomatic, as the slow temporal progression permits compensation due to pericardial stretching. The clinical presentation suggests chronic cardiac failure and constrictive pericarditis with pleural effusion, ascites, and anasarca. EKG findings include bradycardia and microvoltage complexes. Treatment with thyroid hormone replacement is nearly always followed by steady regression of the effusion. Pericardiocentesis is indicated for tamponade, after a confirmatory echocardiogram. This presentation illustrates the importance of detecting hypothyroidism as cause for cardiac tamponade. Prompt diagnosis is vital to prevent cardiogenic shock, and includes early suspicion on the basis of a detailed physical examination, and rapid diagnosis by thyroid functions and echocardiography. Evacuation of the pericardial fluid, and thyroid replacement therapy leads to complete regression and resolution of the condition. IMPLICATIONS/DISCUSSION: Hypothyroidism may lead to cardiac tamponade. Prompt diagnosis is vital to prevent cardiogenic shock. Complete resolution of pericardial fluid following evacuation and thyroid replacement therapy.