Radioiodine uptake in inactive pulmonary tuberculosis

Radioiodine may accumulate at sites of inflammation or infection. We have s een such accumulation in six thyroid cancer patients with a history of prev iously treated pulmonary tuberculosis. We also review the causes of false-p ositive radioiodine uptake in lung infection/inflammation. Eight foci of ra dioiodine uptake were seen on six iodine-123 diagnostic scans. In three foc i, the uptake was focal and indistinguishable from thyroid cancer pulmonary metastases from thyroid cancer. In the remaining foci, the uptake appeared nonsegmental, linear or lobar, suggesting a false-positive finding. The up take was unchanged, variable in appearance or non-persistent on follow-up s cans and less extensive than the fibrocystic changes seen on chest radiogra phs. In the two patients studied, thyroid hormone level did not affect the radioiodine lung uptake and there was congruent gallium-67 uptake. None of the patients had any evidence of thyroid cancer recurrence or of reactivati on of tuberculosis and only two patients had chronic intermittent chest sym ptoms. Severe bronchiectasis, active tuberculosis, acute bronchitis, respir atory bronchiolitis, rheumatoid arthritis-associated lung disease and funga l infection such as Allescheria boydii and aspergillosis can lead to differ ent patterns of radioiodine chest uptake mimicking pulmonary metastases. Pu lmonary scarring secondary to tuberculosis may predispose to localized radi oiodine accumulation even in the absence of clinically evident active infec tion. False-positive radioiodine uptake due to pulmonary infection/inflamma tion should be considered in thyroid cancer patients prior to the diagnosis of pulmonary metastases.