Incidence of postradioiodine immunogenic hyperthyroidism/Graves' disease in relation to a temporary increase in thyrotropin receptor antibodies after radioiodine therapy for autonomous thyroid disease.
BACKGROUND
The aim of the study was to analyze retrospectively the incidence of postradioiodine immunogenic hyperthyroidism/Graves' disease in relation to a temporary increase in TSH-receptor antibodies without overt hyperthyroidism after radioiodine therapy for autonomous thyroid disease.


METHODS
Between May 2000 and May 2003 all patients (n = 1,357) who had undergone radioiodine therapy for autonomous thyroid disease were retrospectively analyzed for development of postradioiodine immunogenic hyperthyroidism. On pretreatment evaluation 565 of 1,357 patients (41.6%) had unifocal autonomous thyroid disease (UFA), 693 of 1,357 patients (51.1%) had multifocal autonomous thyroid disease (MFA), and 99 of 1,357 patients (7.3%) had diffuse thyroid disease (DISS). Free triiodothyronine (FT(3)), free thyroxine (FT(4)), thyrotropin (TSH), and thyroid antibodies were measured. Ultrasound examinations and thyroid scintigraphy were performed before and after radioiodine therapy. A sensitive assay with the human TSH receptor as antigen was chosen for measurement of the TSH receptor antibody and the study was limited to analysis of data obtained since introduction of this assay.


RESULTS
Fifteen of 1,357 patients (1.1%) (UFA, 8/565 = 1.4%; MFA, 6/693 = 0.9%; DISS 1/99 = 1.0%) developed postradioiodine hyperthyroidism between 1 and 13 months after radioiodine therapy with clinically overt hyperthyroidism and an elevation of TSH receptor antibodies. Patients with elevated thyroid peroxidase (TPO) antibodies before radioiodine therapy had an almost 10-fold (6/57 patients =10.5%) higher risk of developing postradioiodine immunogenic hyperthyroidism. Thirteen of 999 patients (1.3%) with antibody measurements after radioiodine therapy (UFA, 2/421 = 0.5%; MFA, 9/494 = 1.8%, DISS, 2/84 = 2.4%) had increased levels of TSH receptor antibodies and, to some extent, TPO antibodies without development of clinically overt hyperthyroidism.


CONCLUSIONS
There is an estimated 1.1% risk of developing postradioiodine immunogenic hyperthyroidism/Graves' disease in patients undergoing radioiodine therapy for autonomous thyroid disease and this increases approximately 10-fold when TPO antibody levels are elevated before radioiodine therapy. Furthermore, there is an estimated 1.3% risk of a temporary increase of TSH receptor antibodies after radioiodine therapy for autonomous thyroid disease without development of clinically overt hyperthyroidism.
Department of Nuclear Medicine, Informatics and Epidemiology, University of Cologne, Cologne, Germany. Matthias.Schmidt@uni-koeln.de
Matthias
M
Schmidt
Eva
E
Gorbauch
Markus
M
Dietlein
Michael
M
Faust
Hartmut
H
Stützer
Wolfgang
W
Eschner
Peter
P
Theissen
Harald
H
Schicha
D006111:Graves Disease / Q000209:etiology*; D006801:Humans; D006980:Hyperthyroidism / Q000209:etiology*; D007453:Iodide Peroxidase / Q000097:blood; D007457:Iodine Radioisotopes / Q000009:adverse effects*; D011832:Radiation Injuries / Q000209:etiology*; D011869:Radioligand Assay; D011989:Receptors, Thyrotropin / Q000276:immunology*; D012189:Retrospective Studies; D016606:Thyroid Nodule / Q000532:radiotherapy
D007457:Iodine Radioisotopes; D011989:Receptors, Thyrotropin; D007453:Iodide Peroxidase