False-Positive Findings on 131I Whole-Body Scans Because of Posttraumatic Superficial Scabs

Nonspecific 131I uptake may affect both the specificity and the accuracy of whole-body scanning (WBS) performed after 131I administration in the follow-up of thyroid carcinoma after thy-roidectomy. We report a newly identified cause of false-positive WBS findings: posttraumatic superficial scabs. Methods: Four patients who underwent thyroidectomy for differentiated thyroid carcinoma were studied after therapeutic administration of 3,700 MBq 131I. Results: WBS revealed an area of uptake in the lower limbs, in a site corresponding to a slight abrasion of the skin that had incidentally occurred between a few hours before and 24 h after radioiodine administration. In 2 patients, a radio-iodine concentration in the scab was shown by the disappear-ance of the radioactivity in the leg after removal of the scab and by detection of radioactivity in the collected material. Conclusion: Posttraumatic superficial scabs may be a cause of false-positive WBS findings. High 131I doses, although providing increased sensitivity, may also increase the number of false-positive results. Key Words: thyroid carcinoma; 131I; whole-body scan; false-positive; sca