MON-575 Clinical Implication of Sonographic Evaluation for Immune Checkpoint Inhibitor-Related Thyroiditis: A Case Series Study

Background: Although immune-related thyroiditis induced by immune checkpoint inhibitors (ICIs) is a common adverse event, its natural course and sequelae is not well understood. In this study, we aimed to evaluate sonographic features of thyroid in patients presenting thyrotoxicosis after ICI treatment, and to figure out whether the findings could predict the clinical course of thyroiditis. Materials and Methods: We analyzed five consecutive cases with thyrotoxicosis associated with ICI, which modulates cytotoxic T-lymphocyte antigen-4, programmed cell death protein-1, or it ligand PD-L1 in a single tertiary cancer center. All patients had normal baseline thyroid function prior to starting ICIs. Thyroid function was evaluated until 24 weeks after starting ICIs. Results: ICIs included pembrolizumab (n=2), durvalumab (n=2), and atezolizumab (n=1). Cancer diagnoses observed were lung cancer (n=3), cervix cancer (n=1), and transitional cell carcinoma (n=1). All patients presented with painless thyroiditis and 3 (60.0%) patients were asymptomatic during the thyrotoxicosis phase. Median time from starting ICI to thyrotoxicosis was 4.0 weeks. Mild enlargement of thyroid glands and low echogenicity were observed on ultrasonography in four patients (80.0%). Hypothyroidism developed in all of them at a median of 6.8 weeks after thyrotoxicosis, and these patients remained on levothyroxine at 24 weeks after ICI treatments. Anti-thyroglobulin antibodies (TgAbs) and/or anti-thyroid peroxidase Abs were positive in three of them (75.0%). One patient (20.0%) showed normal thyroid glands on ultrasonography and was positive for TgAb. She developed hypothyroidism at 18 weeks after thyrotoxicosis and remained on levothyroxine at 24 weeks after ICI. No patient with Graves’ disease was observed. Conclusion: In the present cases, ICI-induced thyrotoxicosis is associated with painless thyroiditis. Sonographic features suggestive of chronic thyroiditis seem to be relevant to the development of hypothyroidism. However, even if sonographic features are normal, progression of thyrotoxicosis to hypothyroidism cannot be excluded.