TSH suppression by octreotide in differentiated thyroid carcinoma

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.

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 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).

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.

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.

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.