SERUM THYROGLOBULIN AND I-131 WHOLE-BODY SCAN IN THE DIAGNOSIS AND ASSESSMENT OF TREATMENT FOR METASTATIC DIFFERENTIATED THYROID-CARCINOMA

Because of the limitations of periodic I-131 whole-body scans, includi ng suspension of substitution therapy, questionable sensitivity and lo w yield in detecting metastases in patients who have undergone thyroid ectomy, serum thyroglobulin and I-131 whole-body scans were evaluated for sensitivity in detecting local, regional or distant metastases in 261 patients with differentiated thyroid carcinoma after total thyroid ectomy and ablation. Methods: A noncompetitive immunoradiometric assay was used for serum thyroglobulin determination. An I-131 whole-body s can was obtained after replacement therapy had been suspended for 6 wk or when TSH reached levels higher than 50 mu U/ml. In patients who un derwent radiological procedures with iodinated contrast media, the wai ting period before the I-131 whole-body scan was no less than 10 wk. R esults: Of the 58 patients with proven metastases who were followed fo r 12 yr (mean 7 +/- 3.3 yr), 51 (88.4%) had high serum thyroglobulin a ssays performed while under full replacement therapy and 32 (55%) show ed clear I-131 whore-body scan localization. There were no instances o f positive whole-body scans and negative serum thyroglobulin. Conclusi on: In patients treated with I-131, serum thyroglobulin assay was an e xcellent method to assess treatment. Patients with metastatic disease and negative whole-body scans with or without serum thyroglobulin exhi bited a trend toward higher mortality. This trend may also indicate th at the lack of I-131 trapping and low thyroglobulin is a sign of metab olic dedifferentiation of otherwise histologically differentiated thyr oid tumors.