Management of cancer thyroid: Is there a role for carbimazole?

Objectives Thyroglobulin (Tg) levels and the uptake of 131I (RAIU)on a whole body scan (WBS) in follow-up of differentiated thyroid carcinoma (DTC) depend on TSH stimulation, which in thyroidectomized patients (pts) can be obtained either by withdrawal of thyroxine (T4) or by administration of recombinant human TSH (rhTSH). As rhTSH is expensive and not available in our hospital we investigated whether carbimazole can be used to increase TSH level in pts with DTC with low TSH inspite of T4 withdrawal.

Methods It is a prospective study included 15 DTC pts with TSH failed to rise to >30 mIU/L at the time of I-131 WBS due to large residual seen in U/S or functioning metastasis and surgery cannot be done. All pts had low TSH less than 30 mIU/ after T4 withdrawal for 4 w. All pts received 2 tablets Carbimazole 5 mg 2x3 daily for 2 w and then check TSH level, if it is >30 mIU/L proceed for I-131 WBS if not continue with higher Carbimazole dose (3x3) for 1 or 2 more w and then check TSH. We reviewed the I-131 WBS of those pts with successful elevation of TSH to assess RAIU. The end point of this is TSH level is >30 mIU/L or maximum 4 w of Carbimazole intake. Paired samples t-test used to compare between TSH levels before and after Carbimazole.

Results TSH elevated to >30 mIU/L in 7 pts received 2x3 Carbimazole for 2 w. The other 7 pts increased Carbimazole dose to 3 x 3 daily for additional 1 or 2 w. 4 of these 7 pts showed TSH of >30 mIU/L. In 11 pts out of 15 (73.3%) TSH increased to >30 mIU/L and their I-131 WBS showed significant RAIU in residual thyroid tissue/ tumor in the thyroid bed and four of them showed distant metastasis. The mean TSH level before Carbimazole is 9.957±5.9 mIU/L and 25.8± 14.6 mIU/L after Carbimazole with significant statistical difference and P < 0.0001.

Conclusions In thyroid cancer pts with large residual thyroid tissue/tumor or functioning metastasis and low TSH level inspite of thyroxin withdrawal and rhTSH is not available, Carbimazole can be used to enhance TSH level to allow diagnosis and treatment with radioactive iodine.