Apathetic thyrotoxicosis due to hemorrhage into a hyperfunctioning thyroid nodule after excessive anticoagulation.

Hyperfunctioning thyroid nodule was diagnosed in a 72-year-old woman. When the nodule reached a diameter of 3.5 cm, overt thyrotoxicosis of the apathetic type was precipitated by hemorrhage into the nodule during a period of excessive anticoagulation. All abnormal physical signs and symptoms as well as laboratory findings returned to normal within a month, without any specific treatment. It was possible to follow this process by repeated B-mode sonographic examinations and thyroid scans.