Echocardiographic evaluation of pericardial effusion in myxedema. Incidence and biochemical and clinical correlations.

Pericardial effusion is a recognized consequences of myxedema. Its incidence is unknown, primarily because of past difficulties in establishing the diagnosis. We studied 33 hypothyroid patients by echocardiography. Ten of the 33 patients (30%) had positive echoes for pericardial effusion. Seven of these ten patients had enlarged hearts on chest X-ray. Five patients had cardiac enlargement but no echo evidence of pericardial effusion. Serum concentrations of thyroxine, 1.8+/-0.3 vs 1.5+/-0.1 mcg/dl and of thyroid stimulating hormone, 34+/-4 vs 38+/-5 muU/ml did not differ in the groups with and without pericardial effusion, respectively. However, the pericardial effusion group had significantly slower heart rates on ECG than those without pericardial effusion: 53+/-8 vs 68+/-2 beats/min, P less than 0.05. Low voltage was present in five of the ten patients with pericardial effusion and five of the 23 nonpericardial effusion patients. None of the patients with pericardial effusion developed tamponade. Seven patients with pericardial effusion were restudied after periods of thyroxine replacement therapy ranging from six months to two years. All were euthyroid and had negative echoes on follow-up, but two still showed cardiomegaly on chest X-ray (both had associated coronary artery disease). We conclude that pericardial effusion occurs frequently in patients with myxedema. Tamponade is uncommon and the effusions disappear with thyroid replacement therapy. Cardiomegaly on chest X-ray and low voltage on ECG are not reliable indicators of pericardial effusion.