Context: The reactivation of Graves' orbitopathy (GO) after radioiodine (RAI) for Graves' disease (GD) is a known effect and its clinical relevance is controversial. Prevention of RAI-induced GO activation is possible in at risk patients with oral glucocorticoids (OGC).

Objectives: To analyze the effects of RAI on GO with or without prophylactic steroids based on known risk factors. To compare the effectiveness of prophylaxis with intravenous steroids (IVGC) and OGC.

Design: Retrospective study. Patients assessed prior and 1–12 months after RAI.

Patients and setting: 113 patients were included in the study. 83 underwent RAI without prophylactic steroids for the absence of risk of activation and 30 were treated with either OGC (n=21) or IVGC (n=9).

Main Outcome Measures: We analyzed the prevalence of GO activation with or without steroid prophylaxis and the difference in the prevalence of GO activation after OGC or IVGC.

Results: GO activation was observed in 7.2% of patients without and in 33.3% of patients with steroid prophylaxis (P<0.0001), for an overall prevalence of 14.6%. GO activation occurred in 47.6% of patients treated with OGC but in none of 9 patients treated with IVGC (P=0.0001). Disease activation was more prevalent in males (P<0.02) and in older patients (P=0.04) with a shorter duration of GD (P<0.01) and time from GO onset (P<0.01).

Conclusions: GO may occur after RAI in approximately 15% of patients also in the absence of signs of active GO. Prophylactic OGC did not prevent GO activation in a large proportion of patients, compared to IVGC.