Objective: This study evaluates the addition of octreotide and L-thyroxine to shorten the period of exposure to unduly elevated TSH levels in patients with differentiated thyroid carcinoma undergoing total body scan with 131I.
Design: Fourteen thyroidectomized patients were studied after total body scan and the restarting of different doses of thyroxine. After one year a second total body scan and a schedule of the same dose of thyroxine combined with octreotide were performed in each subject.
Patients: Patients were divided into four groups according to the treatment: seven patients received initially 100 micrograms of L-thyroxine (Group 1) and after 1 year 100 micrograms of L-thyroxine plus 300 micrograms of octreotide/day (Group 3); the other seven received initially 150 micrograms of L-thyroxine (Group 2) and then 150 micrograms of L-thyroxine plus 300 micrograms 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 elevated in all four groups ranging from 104 to 91 mU/I without significant differences. The patterns of TSH inhibition were however different in the four groups studied. TSH remained very elevated for a long time in Group 1 patients: at day 90 the TSH value was still 2.1 +/- 1.2 mU/I (mean +/- SEM). Patients in Groups 2 and 3 showed a similar pattern: TSH was suppressed in 45 days. The most rapid TSH inhibition was observed in Group 4 patients with a mean decrease of 88% in 14 days and complete suppression in 30 days.
Conclusions: TSH suppression by L-thyroxine is very slow and it can be significantly enhanced by combined octreotide administration. Combined therapy is safe and offers an alternative choice when high dosages of L-thyroxine are inappropriate or in conditions of advanced illness.