False-positive findings on (131)I whole-body scans because of posttraumatic superficial scabs.

UNLABELLED

Nonspecific (131)I uptake may affect both the specificity and the accuracy of whole-body scanning (WBS) performed after (131)I administration in the follow-up of thyroid carcinoma after thyroidectomy. 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 (131)I.

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 radioiodine concentration in the scab was shown by the disappearance 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 (131)I doses, although providing increased sensitivity, may also increase the number of false-positive results.