Relationships between metastases of differentiated thyroid carcinoma and serum thyrotropin (TSH) levels

In a group of 113 patients who had undergone thyroid ablation for differentiated thyroid carcinoma, serum levels of TSH were measured 12 and 17 days after discontinuation of triiodothyronine (T ₃) treatment. On both occasions a wide scattering of TSH levels was found. In patients without metastases, TSH levels varied between 23 and 330 μU/ml (mean ± SD 142 ± 81 μU/ml) at day 12 and between 50 and 380 μU/ml (mean ± SD 212 ± 95 μU/ml) at day 17. In patients with metastases, TSH levels varied between 35 and 315 μU/ml (mean ± SD 145 ± 64 μU/ml) at day 12 and between 45 and 330 μU/ml (mean ± SD 179 ± 74 μU/ml) at day 17. No significant difference between TSH levels of patients with and without metastases was found at day 12, while the difference was significant at day 17. In both groups of patients the increase of TSH levels from day 12 to day 17 was statistically significant. In most patients the reduction or disappearance of metastases by ¹³¹I treatment was followed by a significant increase of serum TSH at day 12: before mean ± SD 113 ± 48 μU/ml, after mean ± SD 162 ± 62 μU/ml. On the other hand, only slight changes of TSH levels were found in a group of patients without metastases repeatedly studied during the same period (1st observation mean ± SD 148 ± 72 μU/ml, 2nd observation mean ± SD 149 ± 64 μU/ml). The results show that, even though hormone production by metastases may influence TSH secretion to some extent, TSH levels after withdrawal of the replacement therapy are mainly related to the individual pituitary response rather than to the presence or absence of metastases. However, an increase of TSH levels after ¹³¹I treatment may be used as a parameter to check the efficiency of ¹³¹I treatment itself.