Administration of a single low dose of recombinant human thyrotropin significantly enhances thyroid radioiodide uptake in nontoxic nodular goiter

Radioiodine (I-131) is increasingly used as treatment for volume reduction of nontoxic, nodular goiter. A high dose of I-131 is often needed because o f low thyroid radioiodide uptake (RAIU). We investigated whether pretreatme nt with a single, low dose of recombinant human TSH (rhTSH; Thyrogen, Genzy me Transgenics Corp.) enhances RAIU in 15 patients with nontoxic, nodular g oiter (14 women and 1 man; aged 61 +/- 11 yr). Four patients were studied t wice, and 1 patient was studied 3 times. RAIU was measured both under basal conditions and after pretreatment (im) with rhTSH, given either 2 h (0.01 mg; n = 7) or 24 h [0.01 mg (n = 7) or 0.03 mg (n = 7)] before 131I adminis tration (20-40 mu Ci). Serum levels of TSH, free T-4 (FT4), and total T-3 w ere measured at 2, 5, 8, 24, 48, 72, 96, and 192 h after rhTSH administrati on. After administration of 0.01 mg rhTSH, serum TSH rose from 0.7 +/- 0.5 to a peak level of 4.4 +/- 1.1 mU/L (P < 0.0001), FT4 rose from 16.0 +/- 2.6 to 18.5 +/- 3.7 pmol/L (P < 0.0001), and T-3 rose from 2.10 +/- 0.41 to 2.63 +/- 0.66 nmol/L (P < 0.0001). After administration of 0.03 mg rhTSH, TSH ro se from 0.6 +/- 0.4 to 15.8 +/- 2.3 mU/L (P < 0.0001), FT4 rose from 15.2 /- 1.5 to 21.7 +/- 2.9 pmol/L (P < 0.0001), and T-3 rose from 1.90 +/- 0.43 to 3.19 +/- 0.61 nmol/L (P < 0.0001). Peak TSH levels were reached at 5-8 h and peak FT4 and T-3 levels at 8-96 h after rhTSH administration. Administration of 0.01 mg rhTSH 2 h before I-131 increased 24-h RAIU from 3 0 +/- 11% to 42 +/- 10% (P < 0.02), 0.01 mg rhTSH administered 24 h before I-131 increased 24-h RAIU from 29 +/- 10% to 51 +/- 10% (P < 0.0001), and 0 .03 mg rhTSH administered 24 h before I-131 increased 24-h RAIU from 33 +/- 11% to 63 +/- 9% (P < 0.0001). After administration of 0.01 mg rhTSH 2 h b efore I-131, 24-h RAIU did not increase in 1 patient, whereas the increase in 24-h RAIU was less than 10% in 2 other patients. In contrast, administra tion of rhTSH 24 h before I-131 increased 24-h RAIU by more than 10% in all 14 patients (by >20% in 10 and by >30% in 6). In conclusion, pretreatment with a single, low dose of rhTSH in patients wi th nontoxic, nodular goiter increased RAIU considerably. Our observations h old promise that administration of rhTSH before 131I therapy for nontoxic, nodular goiter will allow treatment with lower doses of I-131 in these pati ents.