Subtle changes in serum thyrotrophin (TSH) and sex-hormone-binding globulin (SHBG) levels during long-term follow-up after radioactive iodine in multinodular non-toxic goitre.

OBJECTIVE

We investigated possible changes in the pituitary-thyroid axis after radioactive iodine (RAI) treatment of multinodular non-toxic goitre.

DESIGN

Consecutive patients with multinodular non-toxic goitre, who remained euthyroid after radioactive iodine (RAI) treatment.

PATIENTS

Twenty-three women with multinodular non-toxic goitre were followed after treatment with RAI.

MEASUREMENTS

Free T4 index (FT4I), FT3I, free T4, SHBG (immunoradiometric assay), and a third-generation TSH assay (chemiluminetric assay) TSH were measured.

RESULTS

Three weeks after RAI treatment TSH had decreased and SHBG increased (P < 0.05). Only 2/18 patients actually had suppressed TSH values, while 12/18 had values in between euthyroid and toxic levels. Trend analysis from 1.5 to 24 months after RAI treatment demonstrated a progressive increase in TSH (P < 0.01) and gradual decrease in SHBG (P < 0.02). No changes in FT4I, FT3I, or free T4 were found.

CONCLUSION

A third-generation TSH assay gave detailed information about changes in thyroid status when TSH was below normal values. FT4I, FT3I, and free T4 seem to be less sensitive parameters than TSH and SHBG for recording subtle changes in thyroid status after RAI treatment of nodular non-toxic goitre. We demonstrated that changes in the pituitary-thyroid axis continue for a long time after RAI treatment of multinodular non-toxic goitre. These patients should be followed up in order to detect possible late hypothyroidism.