Recombinant TSH is effective in providing exogenous TSH stimulation for patients with differentiated
thyroid cancer on
thyroid hormone-suppressive
therapy. It allows for detection of thyroid remnant and
metastases by radioiodine scan and by serum
thyroglobulin determination. The sensitivity and image quality of the WBS are similar after rTSH and after THSH withdrawal in the majority of patients. The equivalent 100% sensitivity of rTSH- and withdrawal-stimulated serum
thyroglobulin measurement alone in identifying patients with radioiodine uptake outside the thyroid bed [38] may eventually lead to more extensive use of serum
thyroglobulin testing after rTSH, with more selective application of radioiodine WBS [39]. Currently, a phase IV trial is in progress to evaluate the efficacy of rTSH-stimulated
thyroglobulin levels as the primary modality for long-term follow-up of low risk
thyroid cancer patients. The use of rTSH prevents the morbidity, metabolic impairment and the risk of
tumor progression associated with THST withdrawal, because of shorter exposure time to elevated TSH [38]. Furthermore, it decreases the radiation exposure of healthy tissues due to faster
iodine clearance in euthyroidism. rTSH is well tolerated, with transient
nausea in 10.5% and
headache in 7.3% of patients. No
antibodies specific to rTSH were documented, even after multiple courses of the
drug. Currently, rTSH is suggested for patients who do not respond to
hormone withdrawal or cannot tolerate
hypothyroidism. For patients with low risk of
tumor recurrence, rTSH-stimulated testing may be used at 6-12 months after postoperative I-131 ablation and with a repeat cycle of rTSH one year later, followed by testing every 3-5 years. In high risk patients, one set of negative I-131 scan and
thyroglobulin test results after
hormone withdrawal are recommended before using rTSH testing, because of a greater sensitivity of the withdrawal scan and because rTSH is not currently approved for subsequent I-131
therapy often indicated in these patients [24]. Subsequently, two cycles of rTSH testing are recommended at 6-12 month intervals, followed by testing every 1-3 years for at least the first decade after initial diagnosis. The cost of this commercially available form of rTSH has been considered a major impediment to its common use; however, this should be weighed against the loss of productivity of working hours related to withdrawal [40]. In the therapeutic setting, rTSH is the only acceptable option in a subgroup of patients with
hypopituitarism,
ischemic heart disease, a history of "
myxedema madness," debilitation due to advanced disease, or inability to elicit TSH elevation due to continued production of
thyroxine by thyroid remnant or metastatic
tumor [33,38]. In conclusion, recombinant TSH facilitates the management of patients with differentiated
thyroid carcinoma. It increases the sensitivity of
thyroglobulin testing during
thyroid hormone suppression
therapy and enables radioiodine uptake for whole-body scan and occasionally for radioiodine
therapy, without the need for prolonged THST withdrawal and its associated
hypothyroidism, reduced quality of life and risk of
tumor progression.