Background: Recombinant human TSH (rhTSH) is available for monitoring differentiated thyroid carcinoma. rhTSH testing modifies the guidelines for this disease.
Methods: A 2-year experience with rhTSH on 27 consecutive patients with papillary cancer is reported. The aim of the study was to evaluate the sensitivity and specificity of thyroglobulin (Tg) after rhTSH in detecting residual thyroid cancer after primary therapies. Sensitivity and specificity of rhTSH testing were also compared with neck ultrasound (US) and whole-body scan (WBS). Favourable results were regarded as: Tg levels <1 microg/L after rhTSH, no US image indicative of thyroid tissue or suspect neck nodes, and negative WBS after (131)I and (99m)Tc-MIBI.
Results: Side effects were mild. Unfavourable baseline Tg levels were noted in 15% of patients with local or metastatic disease. After rhTSH testing, unfavourable Tg levels were noted in a further 17% of patients. After 12-24 months, Tg levels on rhTSH re-testing were favourable in 14 out of 17 patients evaluated and indicative of no disease progression in 1; in 2, they were still indicative of an unsatisfactory effect of further radioiodine therapy. No significant increase in a subunit (alphaSU) was noted after rhTSH administration. Sera from patients with hypothyroidism or collected on the day of TSH peak after rhTSH, showed isoform profiles of TSH (and alphaSU) similar to those found after focusing rhTSH. Agreement between rhTSH testing and neck US was found in 85% of patients. Agreement among rhTSH, neck US and (131)I and (99m)Tc-MIBI WBS was found in 46% of subjects. The specificity of rhTSH testing, neck US, (131)I and (99m)Tc-MIBI WBS was 95%, 84%, 89% and 53%, while sensitivity was 100%, 87%, 40% and 71%, respectively.
Conclusions: Our data show that full bioactivity of TSH after rhTSH is indirectly suggested by the negligible increase in alphaSU after rhTSH and the similar pattern of TSH isoforms after rhTSH and hypothyroidism. Neck US is the most sensitive imaging technique in detecting local or neck node recurrence of the disease, while (99m)Tc-MIBI WBS is the least specific. After primary treatments for papillary thyroid carcinoma, rhTSH testing under L-T4 therapy and neck US may be regarded as first-line evaluations. Under L-T4 regimen, Tg levels lower than 1 microg/L after rhTSH testing seem to be the best index of normality on follow-up in patients with a history of thyroid papillary carcinoma. In these patients, diagnostic (131)I WBS seems to be unnecessary.