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Cohort Study on Radioactive Iodine-induced Hypothyroidism - Implications for Graves' Ophthalmopathy and Optimal Timing for Thyroid Hormone Assessment.
MedLine Citation:
PMID:  23205939     Owner:  NLM     Status:  Publisher    
Background: Graves Ophthalmopathy (GO) develops or worsens in up to 1/3 of patients treated with radioactive iodine (RAI) for Graves' hyperthyroidism. We sought to identify the prevalence of development or worsening of GO in patients treated with RAI for Graves' hyperthyroidism and to identify risk factors associated with that outcome. Methods: We identified a retrospective cohort of consecutive patients treated with RAI at Mayo Clinic in Rochester, MN between 2005 and 2006. We assessed their medical records for evidence of hypothyroidism and development or worsening of GO in the year following therapy. Hypothyroidism was defined as TSH > 3.0 mIU/L or free thyroxine (fT4) < 0.8 ng/dL. Results: We identified 291 consecutive patients who received RAI therapy during the study period, with 195/291 having complete follow-up data for a 1 year period. GO was present in 46/195 patients (23.6%) at baseline. After RAI treatment GO developed or worsened in 25/195 patients (12.8%) and was associated with hypothyroidism at first follow-up (p=0.011) with odds ratio (OR) of 3.3 (95% CI 1.3 - 8.7). More smokers than non-smokers developed new/worse GO (17.7% versus 11.8%), but that difference did not reach statistical significance (p=0.35). Preexisting GO (24% of patients) was associated with a higher risk for negative GO outcome compared with patients who had no GO at baseline (11%; p=0.021). Both development of hypothyroidism by the first visit post RAI therapy (OR 3.6) and preexistent GO (OR 2.8) remained significant in a multivariate analysis. Development of hypothyroidism was more likely in patients with longer duration to first follow-up (P<0.001). By 6-8 weeks following RAI treatment, the prevalence of hypothyroidism was approximately 40%, while that of hyperthyroidism was only 20%. Conclusions -The presence of hypothyroidism at the first assessment of thyroid function after RAI administration is a strong predictor for adverse GO outcome. This risk is highest in patients with preexisting GO. We suggest that in order to prevent clinical hypothyroidism and the associated risk for GO, the optimal time for first measurement of fT4 is prior to 6 weeks following RAI therapy.
Marius Stan; Jolanta M Durski; Juan P Brito; Sumit Bhagra; Prabin Thapa; Rebecca S Bahn
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-12-4
Journal Detail:
Title:  Thyroid : official journal of the American Thyroid Association     Volume:  -     ISSN:  1557-9077     ISO Abbreviation:  Thyroid     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2012-12-4     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9104317     Medline TA:  Thyroid     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Mayo Clinic, Medicine, Rochester, Minnesota, United States;
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