Summary
Two earlier studies of Graves’ Disease that found that treating Graves’ Disease with radioactive iodine rather than antithyroid drugs caused a large (3-5X) increase in the risk of developing Graves’ Opthalmopathy (GO), an eye disorder. However, there were also five other studies that found no link between radioactive iodine and GO.The difference between the two sets of studies is that the first two studies were randomized controlled trials – the “gold standard” of medical research. In these types of studies, new patients are randomly assigned to a treatment (radioactive iodine (RAI) or anti-thyroid drugs (ATD)) and their outcomes are measured. The 5 studies that found no effect were “retrospective” studies – meaning that they were done by reviewing the medical records of patients after-the-fact. These types of studies aren’t as good because there are more opportunities for things to go wrong. What if patients with the most severe GD or GO opted for the radioiodine treatment instead of drug treatment? What if the mildest patients didn’t return for follow-up? What if the poorest patients chose drugs because they were cheaper? There are many ways that a retrospective study can be intentionally or unintentionally biased.
Because of this history of different results, the authors of this study did a new randomized-controlled trial (although, because of low sample numbers, they also included some patients who chose their treatment).
46 patients with Graves’ Disease were studied. Approximately half received drugs (carbimazole) and the other half received RAI. The two groups started out with similar numbers of smokers (which is thought to increase the risk of GO), existing symptoms of GO, and thyroid hormone levels.
Results: TSH levels were slightly higher in the RAI group than in the ATD group. For all other measures (such as signs of GO and other thyroid hormones), the two groups were the same. The authors concluded that there was no increased risk of GO with RAI treatment.
Discussion: The authors point out some of the problems with the previous two randomized-controlled trials. In one study, there was a much higher number of smokers, which is a known risk-factor for GO. In both studies, the RAI-treated patients were allowed to become hypo-thyroid (too low levels of thyroid), although this is not generally considered a risk factor. The current study had a small sample size (only 46 people, versus 114 and 443 in the other two studies), which makes it harder to pick out differences between groups.
Bottom line: this study found no difference in the development of GO in patients treated with radioactive iodine or carbimazole.
Reference
Samer El-Kaissi et al., “Association between radioiodine therapy for Graves’ hyperthyroidism and thyroid-associated ophthalmopathy,” International Ophthalmology 30, no. 4 (2010): 397-405.
Abstract To investigate the role of radioactive iodine (RAI) in the onset and progression of thyroid-associated ophthalmopathy (TAO). Forty-six Graves’ disease patients with mild or no ophthalmopathy were prospectively treated with carbimazole (CBZ) (n = 22) or RAI (n = 24). Treatment effects were evaluated clinically over 12 months, and with orbital MRI-measured extra-ocular muscle (EOM) volumes at baseline and at 6 months. The diagnosis of TAO was based on the clinical activity score (CAS) system. There were 11/22 CBZ and 10/24 RAI patients with active ophthalmopathy at baseline. Despite greater mean TSH levels post-RAI (P = 0.003), there was no increase in the likelihood of developing active ophthalmopathy (OR 0.95; 95% CI 0.56–1.61, P = 0.9) or EOM dysfunction (OR 0.52; 95% CI 0.26–1.06, P = 0.074). The increased mean palpebral aperture post-RAI (P = 0.023) and greater mean proptosis in the CBZ group (P = 0.005) were not confirmed when the absolute values of these measurements were examined. There was no association between the treatment received and MRI-measured EOM volumes. In this study, RAI therapy for Graves’ disease did not increase the risk of progression or development of ophthalmopathy in patients with mild or no eye disease at baseline.
