Diffuse Iodine-131 lung uptake in bronchiectasis: a potential pitfall in the follow up of differentiated thyroid carcinoma.

Background. I-131 total body scintigraphy is a commonly used post thyroidectomy imaging procedure in the management of differentiated thyroid cancer, in particular in patients with intermediate or high risk of persistent or recurrent disease, in combination with serum thyroglobulin determinations and ultrasound of the neck. It can show the persistence of residual thyroid tissue after thyroidectomy and local and distant metastases. Although this is a highly sensitive method for detecting normal and pathologic thyroid tissue, especially when performed after a radio-ablative dose, false-positive scans (i.e. uptake in the absence of residual thyroid tissue or metastases) can occur in different situations. Patient Findings. We report a case of a 42-yr-old woman with recurrent chest infections and bronchiectasis, who had a total thyroidectomy and I-131 treatment because of a papillary thyroid carcinoma. She presented with marked bilateral I-131 uptake in the lungs mimicking metastatic involvement of the lungs by thyroid cancer but interpreted as nonspecific bilateral uptake by her bronchiectatic bronchial tree. Summary. Our case, as well as others reported in the literature, calls attention to the fact that radioiodine lung uptake may be related to chronic inflammatory lung disease, thus representing a potential diagnostic pitfall in patients with differentiated thyroid cancer. Conclusions. I-131 uptake should be interpreted on the bases of clinical context, imaging and laboratory findings (serum Tg). Recognition of potential false-positive I-131 scans is critical to avoid unnecessary exposure to further radiation from repeated therapeutic doses of radioactive iodine with possible side effects and even worsening of lung disease itself.