Lower cure rates after single dose radioactive iodine treatment for thyrotoxicosis for Māori as compared to New Zealand Europeans

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 281-290-Comparative Effectiveness/Health Outcomes/Quality Improvement/Patient or Provider Education/Endocrine Emergencies
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-282
Jade AU Tamatea1, Helen M Conaglen2, John V Conaglen3 and Marianne Susan Elston*1
1Waikato Hospital, Hamilton, New Zealand, 2Waikato Clinical School, Hamilton, New Zealand, 3Waikato Clinical School, University of Auckland, Hamilton, New Zealand
Introduction: Graves’ disease (GD) and toxic multinodular goitre (TMNG) are the most common causes of thyrotoxicosis. In New Zealand (NZ) radioactive iodine (I131) is the usual definitive therapy, although not all patients are cured by a single dose of I131. Features reported to decrease the effectiveness of I131 include male gender, young age and a large gland1-4.  Although clinical observation suggests that I131is less likely to achieve cure in Māori (the indigenous people of New Zealand), to date this has not been studied. 

Method: Retrospective review of I131 for thyrotoxicosis at Waikato Hospital, NZ during the 3 year period prior to 1 December 2010. Cure was defined as being euthyroid or hypothyroid on replacement at end of follow up, while patients with ongoing Thyroid-Stimulating Hormone (TSH) suppression or those requiring further doses of I131were considered as failure to achieve cure. 

Results: A total of 326 doses of I131 were given to 285 patients. Follow up data were available on 283 patients. Median follow-up was 858.5 days (range 30-1525). 83.4% were female. Mean age was 53.12 years (± 14.96) years. Māori comprised 32% of the patients and NZ Europeans 55%. The diagnosis was GD in 61.1% and TMNG in 34.3%. Most patients (98.2%) received a fixed dose of 555mBq (15mCi). At last follow up cure had been achieved in 72.1%. There was no difference in cure rates according to gender (p=0.1212) or diagnosis (GD 70.5% vs TMNG 73.2% p=0.6377). Younger patients (<50 years) were less likely to achieve cure as compared to >50years (63.7% vs 78.6% respectively, p=0.0059). Māori patients were less likely to achieve cure than NZ Europeans (60.4% vs 77.1% respectively, p=0.0058). Māori were also more likely to be younger (49.80 ± 11.29 years vs 55.84 ± 16.04, p=0.0018) and more likely to have a TMNG (47.3% vs 31.2% p=0.0124). 

Discussion: A fixed dose of I131 successfully cured hyperthyroidism in 72% of patients treated. In the population studied, age <50 years and Māori ethnicity predicted a lower rate of cure from a single dose of I131 therapy.

(1) Allahabadia A, Daykin J, Sheppard MC, Gough SC, Franklyn JA. Radioiodine treatment of hyperthyroidism-prognostic factors for outcome. J Clin Endocrinol Metab. 2001; 86:3611-7. (2) Allahabadia A, Daykin J, Holder RL, Sheppard MC, Gough SC, Franklyn JA. Age and gender predict the outcome of treatment for Graves' hyperthyroidism. J Clin Endocrinol Metab. 2000; 85:1038-42. (3) Metso S, Jaatinen P, Huhtala H, Luukkaala T, Oksala H, Salmi J. Long-term follow-up study of radioiodine treatment of hyperthyroidism. Clin Endocrinol (Oxf). 2004; 61:641-8. (4) Boelaert K, Syed AA, Manji N, Sheppard MC, Holder RL, Gough SC, Franklyn JA. Prediction of cure and risk of hypothyroidism in patients receiving 131I for hyperthyroidism. Clin Endocrinol (Oxf). 2009; 70:129-38.

Nothing to Disclose: JAT, HMC, JVC, MSE

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