TSH SUPPRESSION BY OCTREOTIDE IN DIFFERENTIATED THYROID-CARCINOMA

OBJECTIVE This study evaluates the addition of octreotide and L-thyrox ine to shorten the period of exposure to unduly elevated TSH levels in patients with differentiated thyroid carcinoma undergoing total body scan with I-131. DESIGN Fourteen thyroidectomized patients were studie d after total body scan and the restarting of different doses of thyro xine. After one year a second total body scan and a schedule of the sa me dose of thyroxine combined with octreotide were performed in each s ubject. PATIENTS Patients were divided into four groups according to t he treatment: seven patients received initially 100 mu g of L-thyroxin e (Group 1) and after 1 year 100 mu g of L-thyroxine plus 300 mu g of octreotide/day (Group 3); the other seven received initially 150 mu g of L-thyroxine (Group 2) and then 150 mu g of L-thyroxine plus 300 mu g of octreotide/day (Group 4). MEASUREMENTS Serum TSH, T3 and T4 were measured on the day of radioiodine administration (day 0) and after 14 , 21, 30, 45, 60 and 90 days. RESULTS Mean basal TSH levels were eleva ted in all four groups ranging from 104 to 91 mU/l without significant differences. The patterns of TSH inhibition were however different in the four groups studied. TSH remained very elevated for a long time i n Group 1 patients: at day 90 the TSH value was still 2.1 +/- 2 mU/l ( mean +/- SEM). Patients in Groups 2 and 3 showed a similar pattern: TS H was suppressed in 45 days. The most rapid TSH inhibition was observe d in Group 4 patients with a mean decrease of 88% in 14 days and compl ete suppression in 30 days. CONCLUSIONS TSH suppression by L-thyroxine is very slow and it can be significantly enhanced by combined octreot ide administration. Combined therapy is safe and offers an alternative choice when high dosages of L-thyroxine are inappropriate or in condi tions of advanced illness.