Pericardial effusion. Unusual complication in thyroid cancer.

A case in which a prolonged hypothyroid state resulted in development of a pericardial effusion is presented. The compensatory mechanism for protein homeostasis is lost in severe hypothyroidism. Iodine is transported to the pericardial space, which is filled with a high-protein content fluid and remains trapped. The mechanism for the accumulation of the fluid in the pericardial space is discussed. To prevent this unusual but dangerous complication, the authors recommend close monitoring of the patient's clinical status and serum thyroid stimulating hormone. The use of a short acting thyroxine substitute for at least 2 weeks can decrease occurrence of this complication and will shorten the time the patient needs to be hypothyroid.