The influence of distant metastases on serum TSH elevation after L-T₄ withdrawal in differentiated thyroid cancer

Objective: To investigate the influence of distant metastases on the increase rate (v_x) of serum TSH and its change rate (R_a) in patients with DTC after thyroid hormone withdrawal (THW). Methods: Three times or more serum TSH measurements were performed before and after THW in 97 patients (38 males, 59 females) who had underwent successful ¹³¹I ablation from January 2014 to July 2014. v₁(early period v_x), v₂( later period v_x) and change rate of v_x and v₂(R_a) were calculated and compared between M₀ group (without distant metastases, n = 67) and M₁ group (with distant metastases, n = 30). Two-sample t test and rank-sum test were used for statistical analysis. Results: v₁ in males was significantly higher than that in females ((3.58 ± 2.13) vs (2.63 ± 1.54) mU·L^-1·d^-1; t = 2.549, F = 0.012). v₂ in M₀ group was significantly higher than that in M₁ group ((7.67 ± 3.66) vs (3.68 ± 4.33) mU·L^-1·d^-1; t = 3.613, P = 0.001). The difference of R_a between M₀ group and M₁ group was statistically significant (z = -4.17, P < 0.05). Conclusions: Distant metastases may affect the increase rate and its change pattern of serum TSH after THW. Serum TSH showed a slow elevation over time or even decline in patients with distant metastasis. Meanwhile TSH increased much higher over the THW time in most of the patients in M₀ group. It was suggested that attention should be paid to the variation of serum TSH in DTC patients with distant metastases to avoid decrease of TSH during longer THW. (authors)