Pretreatment with recombinant human TSH changes the regional distribution of radioiodine on thyroid scintigrams of nodular goiters

In a recent study, we demonstrated that pretreatment with a single, low dos e of recombinant human TSH (rhTSH) doubles 24-h thyroid radioactive iodine uptake in patients with nodular goiter. The purpose of the present study wa s to investigate whether rhTSH pretreatment induces changes in the regional distribution of radioiodine as visualized on thyroid scintigrams in these patients. Anterior planar thyroid I-123 scintigrams were obtained in 26 patients with a nodular goiter (23 women and 3 men; age, 62 +/- 9 yr, mean SD; thyroid w eight, 165 +/- 72 g) 24 h after administration of a diagnostic dose of radi oiodine. All patients were studied twice: first, without rhTSH pretreatment (baseline study), and second, after an im injection of 0.01 mg (n = 10) or 0.03 mg rhTSH (n = 16), given 24 h before radioiodine administration (rhTS H study). For quantification of regional differences in radioiodine uptake, a region of interest method was used. Upon visual inspection, baseline scintigrams showed a heterogeneous uptake of radioiodine. In general, rhTSH scintigrams also showed heterogeneous rad ioiodine uptake. In some patients, the distribution of radioiodine in the r hTSH scintigram was considerably more homogeneous than in the baseline scin tigram. In a few patients, originally "cold" areas had changed into "hot" o nes, whereas originally hot areas had changed into cold ones. Quantificatio n of regional radioiodine uptake showed that pretreatment with rhTSH caused a larger increase in radioiodine uptake in relatively cold areas and a sma ller increase in radioiodine uptake in relatively hot areas, compared with the increase in radioiodine uptake in the entire thyroid. In patients with a baseline serum TSH level of 0.5 mU/liter or lower, the increase in radioi odine uptake in relatively cold areas was significantly larger than in pati ents with a baseline serum TSH level higher than 0.5 mU/liter. In conclusion, a single, low dose of rhTSH not only doubled 24-h radioactiv e iodine uptake but also caused a more homogeneous distribution of radioiod ine within the thyroid gland in patients with a nodular goiter by stimulati ng radioiodine uptake in relatively cold areas more than in relatively hot areas. This was most marked in patients with a low baseline serum TSH level . Our data suggest that pretreatment with rhTSH may improve the efficacy of radioiodine treatment for volume reduction of nodular goiters, especially in patients with a low baseline serum TSH level.