Incidental detection of hyperthyroidism during a perfusion lung scan for suspected pulmonary emboli

Striking thyroidal uptake of Tc-99m pertechnetate was observed during the course of a perfusion lung scan performed with Tc-99m MAA to rule out pulmonary embolism in a 49-year-old man. There was no evidence of gastric pertechnetate activity. Radiochemical purity analysis of the Tc-MAA by chromatography in normal saline revealed 98.8% tagging, with 1.2% free pertechnetate. We estimate that a maximum of 60 microCi (2.2 MBq) of pertechnetate was available for thyroid trapping. This amount, given to a euthyroid volunteer studied with conventional gamma camera lung perfusion settings, failed to visualize the thyroid. A follow-up radioiodine thyroid uptake of the patient was markedly elevated, as was his thyroid function tests (T3,T7,T7). When diffuse intense thyroid gland radioactivity is seen during scintigraphy with a technetium radiopharmaceutical (e.g., bone and lung scans), consideration should be given to the possibility of hyperthyroidism. If gastric activity is not concomitantly seen, hyperthyroidism secondary to diffuse hyperplasia of the gland is probably present.