Endocrine Abstracts

The transformation of toxic nodular goitre into autoimmune hyperthyroidism with development of thyrotropin receptor antibodies (TSHRAb) as effect of ¹³¹I therapy is rarely investigated.

The aim of the study is to present cases of patients with toxic nodular goitre who developed autoimmune hyperthyroidism after initial ¹³¹I dose, and results of treatment with second ¹³¹I dose or thyrostatics.

Four patients with toxic nodular goitre received therapeutic dose of ¹³¹I. Thyroid function was assessed by measuring FT₃, FT₄, TSH, TSHRAb levels.

Male aged 44 referred to ¹³¹I treatment (after 6 months) again due to hyperthyroidism. TSHRAb was increased to 3.3 U/l. Three months after administering second ¹³¹I dose, hypothyroidism was diagnosed (TSH 46.74 mIU/l) and substitute treatment was added.

Female aged 40 (TSHRAb <0.3 U/l before ¹³¹I): euthyroidism after 3 months of ¹³¹I therapy; recurrence of hyperthyroidism and an increase in TSHRAb to 5.8 U/l after another 3 months. After administering thyrostatics for 6 months, euthyroidism was achieved. TSHRAb decreased to 0.9 U/l.

Female aged 57 (TSHRAb <0.3 U/l before ¹³¹I): increase in FT₃, FT₄ and TSHRAb to 5.8 U/l after 3 months of ¹³¹I therapy. After administering thyrostatics for 3 months, euthyroidism was achieved. TSHRAb decreased to <0.03 U/l.

Female aged 53 (TSHRAb < 0.3 U/l), after 3 months of ¹³¹I therapy, thyroid function tended to be normal (TSH=0.34 mIU/l); after 6 months there was recurrence of hyperthyroidism with increase of TSHRAb to 1.9 and to 4.0 U/l after another 3 months. When patient was treated with thyrostatics, her thyroid function tended to be normal.

Conclusion: Although insignificant number of patients makes it impossible to analyse results of treatment of autoimmune hyperthyroidism (second ¹³¹I dose versus thyrosatics), it seems that treating patients with thyrostatics before administering possible second dose of radioiodine is justified.