Increased uptake of iodine-131 in metastases of differentiated thyroid carcinoma associated with less severe hypothyroidism following total thyroidectomy.
BACKGROUND
In an attempt to determine possible factors affecting the efficacy of iodine-131 (I-131) treatment for metastatic thyroid carcinoma, the authors focused their efforts on thyroid functions after total thyroidectomy.


METHODS
Between 1980 and 1991, 47 patients with lung metastases of differentiated thyroid carcinoma were treated with I-131. Relationships of the images on post-therapy scans with various clinical features were studied.


RESULTS
Among them, 28 (59.6%) showed I-131 uptake in the metastases on post-therapy scans. Younger patients had lesions that concentrated more radioactive iodine than did those of older patients. The amount of I-131 concentrated in the metastatic lesions correlated with serum triiodothyronine (T3), thyroxine (T4), and thyroglobulin levels and inversely with serum thyroid-stimulating hormone (TSH) levels determined at the time of therapy. Serum T3 and T4 levels were significantly higher in 28 patients with positive scans than in 19 patients with negative scans. Most patients who had metastases with markedly increased radioactivity were euthyroid or mildly hypothyroid, suggesting that thyroid hormones produced by tumor masses compensated for severe hypothyroidism after total thyroidectomy, and showed favorable responses to the treatment. In three patients successfully treated, decreases in serum thyroglobulin levels and the size of metastatic lesions were accompanied by the development of severe hypothyroidism.


CONCLUSIONS
The presence of a large amount of metastatic functioning thyroid tissues responsive to I-131 treatment can be suspected in patients with less severe hypothyroidism after total thyroidectomy.
Kasagi
K
K
Department of Nuclear Medicine, Kyoto University, Japan.
Miyamoto
S
S
Endo
K
K
Sasayama
S
S
Takeuchi
R
R
Hidaka
A
A
Iida
Y
Y
Misaki
T
T
Hatabu
H
H
Konishi
J
J
D000230:Adenocarcinoma / Q000378:metabolism / Q000532:radiotherapy* / Q000601:surgery; D000293:Adolescent; D000328:Adult; D000368:Aged; D002291:Carcinoma, Papillary / Q000150:complications / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000150:complications*; D007457:Iodine Radioisotopes / Q000378:metabolism / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000378:metabolism / Q000556:secondary; D008297:Male; D008875:Middle Aged; D013964:Thyroid Neoplasms / Q000150:complications / Q000532:radiotherapy* / Q000601:surgery; D013965:Thyroidectomy
D007457:Iodine Radioisotopes