The development of transient hypothyroidism after iodine-131 treatment in hyperthyroid patients with Graves' disease: prevalence, mechanism and prognosis.
OBJECTIVE
Recovery of thyroid function in patients following hypothyroidism induced by 131I therapy for Graves' disease has been described, but only a few detailed clinical and biochemical studies of this phenomenon (transient hypothyroidism) have been published. The prevalence, mechanism, and final outcome of transient hypothyroidism in 260 patients with Graves' disease treated with 131I was studied.


METHODS
A retrospective study.


METHODS
Two hundred sixty patients with Graves' disease, treated with 131I between 1 and 15 years previously, were categorized into 4 groups according to their thyroid function during and 1 year after therapy (Group 1: permanent hypothyroidism, 28 patients; Group 2: transient hypothyroidism, 39 patients; Group 3: euthyroidism without transient hypothyroidism, 83 patients; Group 4: hyperthyroidism, 110 patients).


METHODS
We compared total T4, total T3, TSH, anti-thyroglobulin (TGHA) and anti-microsomal (MCHA) antibodies, the TSH-binding inhibitory immunoglobulin (TBII) index, thyroid weight, dose of 131I, and 24-hour 131I uptake as pretreatment variables. The mean time for permanent hypothyroidism to develop was estimated by the Kaplan-Meier product limit method. The TBII index and thyroid stimulating antibody (TSAb) activity were measured in seven patients from Group 1 and in nine patients from Group 2 at the time that they became hypothyroid.


RESULTS
Hypothyroidism developing within 12 months of therapy was transient in 58% (39/67) of patients. No pretreatment variables were found to differ between patients with and without transient hypothyroidism. The mean estimated time between therapy and the development of permanent hypothyroidism was 96 months in Group 2; this time interval was significantly shorter than 126 months in Group 3 and 129 months in Group 4 (P < 0.05, P < 0.01, respectively). TSAb activity was > 500% In 78% (7/9) of patients from Group 2, which was significantly higher than that found (14%, 1/7) in Group 1.


CONCLUSIONS
These results indicate that (1) more than half the patients who developed hypothyroidism within 6 months after 131I treatment for Graves' disease recovered spontaneously, (2) TSAb activity might play some role in the recovery of transient hypothyroidism, and (3) the development of transient hypothyroidism may influence long-term thyroid function.
Aizawa
Y
Y
Second Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Yoshida
K
K
Kaise
N
N
Fukazawa
H
H
Kiso
Y
Y
Sayama
N
N
Hori
H
H
Abe
K
K
D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000378:metabolism; D005260:Female; D006111:Graves Disease / Q000097:blood / Q000503:physiopathology / Q000532:radiotherapy*; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D018828:Immunoglobulins, Thyroid-Stimulating / Q000097:blood; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D011879:Radiotherapy Dosage; D011989:Receptors, Thyrotropin / Q000378:metabolism; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000528:radiation effects; D013963:Thyroid Hormones / Q000097:blood; D013997:Time Factors
D001323:Autoantibodies; D018828:Immunoglobulins, Thyroid-Stimulating; D007457:Iodine Radioisotopes; D011989:Receptors, Thyrotropin; D013963:Thyroid Hormones; C094372:thyrotropin-binding inhibitory immunoglobulin