OUTCOMES OF RADIOACTIVE IODINE THERAPY IN HYPERTHYROID PATIENTS ON EXISTING STEROID THERAPY

A RETROSPECTIVE STUDY

Abstract

INTRODUCTION
Radioactive iodine (RAI) is a common and effective treatment for hyperthyroidism. Corticosteroids are sometimes given as adjunct therapy for hyperthyroidism, or as treatment for thyroid eye disease (TED). Data is lacking on whether pre-existing steroid therapy affects the efficacy of RAI.

METHODOLOGY
We performed a retrospective review of thyrotoxic patients attending our clinic who underwent RAI between Dec 2017 and June 2024 and identified patients who were on corticosteroid therapy prior to RAI. Parameters including age, gender, diagnosis, steroid dosage, fT4, RAI treatment episodes and remission were evaluated. For patients who underwent multiple RAI treatments, only the first RAI treatment was evaluated. Remission was defined as euthyroid or hypothyroid status at least 6 months post-RAI, without the need for additional RAI treatment. Chi-squared test was performed to compare the remission rate with or without prior steroids.

RESULT
Four hundred fifty-two patients underwent RAI, 17 were on steroids. For the steroid group, the mean age was 41.8 ± 9.8 years. Graves' was the predominant diagnosis (76.5%). Mean fT4 pre-RAI was 18.4 ± 9.7 pmol/L, and mean prednisolone dose was 23.8 ± 9.3 mg. Indications for steroids included TED (41.2%), antithyroid drug allergy (17.6%), refractory Graves' (11.8%), agranulocytosis (11.8%), other autoimmune diseases (11.8%) and liver injury (5.9%). Patients with TED were often commenced on steroid therapy for two weeks pre-RAI. Mean RAI dose was 20.2 ± 4.5 mCi for the steroid group and 17.8 ± 4.3 mCi for the non-steroid group (p = 0.028). Remission rate after first RAI treatment was 58.8% in the steroid group vs 73.6% in the non-steroid group. (χ² = 3.5, p = 0.06)

CONCLUSION
We did not find any statistically significant difference in the post-RAI remission rates between the steroid and non-steroid groups. However, there was a trend towards reduced response to RAI in the steroid group. The study was limited by the small number of patients on steroids, and the difference in RAI doses used between groups. Analysis of a larger number of patients is warranted.