Furosemide increases thyroid uptake of radioiodine in an anuric patient: first observation.

To the Editor: Earlier studies demonstrated unexpected decrease of radioiodine (131I) renal excretion in patients adherent to low-iodine diet before 131I treatment while receiving furosemide [1,2]. This effects seems specific for humans, since it was not confirmed in a study on mice treated with low-iodine diet [3]. Other researchers [4-7] observed increase of 131I uptake to thyroid tissue or thyroid remnants, in patients receiving either furosemide or other diuretics after 131I. However, this increase in 131I uptake could be either due to increased radioctivity in blood, probably a simple diffusion of radioactivity from blood to thyroid, or to increased transport of 131I accross thyroid cell membrane, stimulated by diuretics [8, 9]. Observations on a patient as described below suggested a clue to the above mechanism of increased 131I thyroid uptake. This was a male patient, 34 years old, anuric, suffering from terminal renal failure and hemodialized thrice weekly for four hours per session, from June 2010 till today, November 2011. He was diagnosed as having papillary thyroid cancer metastatic to local and regional lymph nodes (pT3N1aMx). After total thyroidectomy, the patient was submitted to whole-body scintigraphy with 111MBq of 131I (using γ-camera e.cam, dual-head, variable angle, Siemens Medical Solutions, USA), which showed an area of radioiodine accumulation at the left side of thyroid bed (2.4% of the administered 131I was fixed to this area at 24h). In order to achieve complete thyroid ablation, 1.95GBq of 131I were given to the patient after being for 15-days on a low-iodine diet and having plasma TSH 45mIU/L. The patient’s consent for the whole procedure was obtained. With an aim to remove unbound 131I from the patient’s body, the patient was hemodialized twice, 24h and 48h after the administration of 131I with separate and controled collection of radioactive waste solutions. Thus, 73% of the administered 131I dose was eliminated, as calculated after measurements of radioactivity of the dialysis waste solution and in blood and by a survey-meter at 2-meters distance from the patient. Seventy-two hours after administration of 131I, whole-body scintigraphy was made using the same gamma camera. One zone of intense 131I accumulation was found in the thyroid bed, at the projection of right thyroid lobe. About 18h from the radioiodine administration the patient experienced an episode of high blood pressure (160/100mmHg), and was given by accident (considering his anuric state) an intravenous injection of 20mg furosemide, the drug which is routinely used for treatment of hypertensive emergencies, due to its direct vasodilating and diuretic effect [10, 11]. Although the patient’s blood pressure dropped to 130/80mmHg, and no deterioration of patient’s health was noted, this event was reported to the hospital Quality Assurance Committee. In order to follow effects of furosemide on 131I, after obtaining consent from the patient nine 2mL samples of venous blood were drawn from the cubital vein at 15min intervals, till nine samples were collected and simultaneously radioactivity in the neck region was measured by a survey meter with pancake probe, leaning on the thyroid region. Obtained values of radioactivity were expressed as percentage of initial radioactivity of blood and thyroid region, recorded before administration of furosemide (Table 1 and Fig. 1). As early as 15min after the administration of furosemide the drop of radioactivity was recorded in the blood and increase of radioactivity was noted in the thyroid region. All remaining 7 measurements of blood and thyroid region radioactivity showed gradual decrease in blood radioactivity and increase in thyroid region (Table 1 and Fig. 1). Using Pearson’s test, we found high reverse correlation (r=-0.968) radioactivity in between changes in blood and in the thyroid region, with high statistical significance (P<0.001).