“Hot Shoes” from Radioactive Iodine Treatment

Dear Editor:

Thyroid remnant ablation with I-131 is the standard of care in management of patients with thyroid cancer after total thyroidectomy. A posttherapy scan is usually acquired about 2 weeks after the treatment to look for additional metastatic disease. Radioactive iodine is excreted physiologically in the urine, sweat, and saliva, and various patterns of accumulation of I-131 activity have been reported (1 –3). We report for the first time intense uptake in the feet and shoes seen on whole-body I-131 scan images of a 74-year-old Caucasian man with history of papillary thyroid cancer and posttotal thyroidectomy. Figure 1A and B shows the anterior and posterior whole-body image acquired 14 days after remnant ablation with 150 mCi of I-131, with the patients' shoes on. Focal uptake is seen in the thyroid remnant and intense symmetric uptake is seen in both feet and shoes. Counts per pixel in the feet and shoes on the whole-body scan averaged about five times higher than the background (thighs). Additional images of the feet (without the shoes on) and images of the shoes alone were also acquired. Anterior and posterior spot views of the feet (Fig. 2A and B) acquired after removing the shoes and cleaning the feet with soap and water show persistent uptake in the plantar aspect, bilaterally. Dorsal and plantar spot views of the shoes alone (Fig. 2C and D) show intense activity in the medial aspect. Clinical examination did not show any lesions on the feet. On questioning, patient said that his feet do not sweat excessively and he keeps good personal hygiene. We attribute this unique pattern of increased activity in bilateral feet and shoes to I-131 excretion in the sweat and progressive accumulation in the shoes. This finding may be missed, as the patients are often not scanned below the knees. Postthyroidectomy, patients who are prepared by thyroid hormone withdrawal and sweat excessively may be advised to wash palms and soles regularly, and change and launder socks daily for up to about 2 weeks (>10 effective half-lives of I-131) after I-131 therapy.

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FIG. 1.

Whole-body anterior (A) and posterior (B) image acquired with the shoes on.

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FIG. 2.

(A) and (B) show anterior and posterior spot views, respectively, of both feet (without shoes) acquired after cleaning the feet with soap and water. (C) and (D) show dorsal and plantar image, respectively, of the patient's shoes.