Single 0.9-mg intramuscular rhTSH dose achieves target TSH levels in differentiated thyroid carcinoma

Differentiated thyroid carcinoma (DTC) is the most common thyroid malignancy, with incidences increasing globally. Radioisotopic therapy with iodine-131 (RAI) is recommended after total thyroidectomy for patients at intermediate/high risk. A new approach that involves the use of recombinant human TSH (rhTSH) to stimulate iodine-131 uptake during RAI has long been approved. In the standard protocol, 0.9 mg of rhTSH is administered intramuscularly on two consecutive days, followed by a therapeutic dose of iodine-131 on day 3. Unlike the traditional method of levothyroxine (LT4) withdrawal, this protocol allows the continuation of LT4, avoiding the symptoms and metabolic consequences of profound hypothyroidism. However, its high cost remains an important limitation in our setting. Therefore, this study evaluated whether a single intramuscular dose (0.9 mg) of rhTSH, instead of the currently recommended two doses, is sufficient to achieve the target thyroid-stimulating hormone (TSH) level (> 30 mIU/L) currently recommended for RAI.

This prospective, cross-sectional study included 88 patients. The TSH level on day 1 (TSH D1), defined as the primary outcome, was evaluated in relation to sex, age, body weight, recurrence risk (ATA 2025), baseline TSH values, and the interval between TSH measurements.

A single rhTSH dose substantially increased TSH levels to > 30 mIU/L in all patients. Age and body weight were independently associated with TSH D1.

These preliminary results support the potential of single-dose rhTSH as a cost-effective and clinically feasible alternative in selected patients with DTC to achieve TSH levels > 30 mIU/L. Future comparative clinical trials should assess iodine uptake, therapeutic response, and long-term oncologic outcomes.