SAT-492 Impending Thyroid Storm Induced by Checkpoint Inhibitors

Abstract Introduction: Thyroid storm is a rare but life threatening condition due to thyroid hormone excess and is usually caused by Graves disease, toxic nodular goiter or rarely due to thyroiditis. Immune checkpoint inhibitors (ICI) are a novel choice for treating cancers, and carry a risk for development of endocrinopathies. We report a case of impending thyroid storm 5 weeks after initiation of ICI. Case Presentation: 81-year-old Caucasian male with metastatic renal cell carcinoma presented with generalized weakness and fatigue 5 weeks after ipilimumab and nivolumab were started. He had no prior history of thyroid disease and had normal thyroid functions before the treatment. He complained of palpitations, heat intolerance and loose stools on admission. On examination he was disoriented, tachycardic (128bpm) with new onset atrial fibrillation, had moist skin and brisk reflexes. He had non-tender thyroid, no thyromegaly, and no nodules palpated. Burch-Wartofsky score was 35, suggesting impending thyroid storm. Laboratory investigation showed elevated free T4 (>7.77), elevated free T3 (8.6) with a suppressed TSH (< 0.02). He had positive anti-TPO but Thyrotropin receptor antibody was negative. He was treated with propranolol 40 mg three times daily, prednisone 40 daily, methimazole 30mg three times a day with significant improvement in free T4 (5.67) within first 48 hours. Discussion: Imipimumab and nivolumab are monoclonal antibodies against cytotoxic T-lymphocyte associated protein 4 (CTLA-4) and programmed death receptor-1 (PD-1) respectively. The reported incidence of thyroid dysfunction after combined imipimumab and nivolumab therapy can be as high as 22%1. Thyroiditis could present as early as 2-6 weeks 2 after treatment, and hypothyroidism tends to present between 5 months and 3 years3. According to a current consensus4, baseline TSH and FT4 should be drawn prior to initiating ICI. Thyroid storm is a clinical diagnosis and Burch-Wartofsky score can help in diagnosis. A high degree of suspicion and prompt diagnosis of thyroid storm and treatment is of utmost importance especially in this patient population. Rapid improvements in thyroid hormone levels suggest thyroiditis as a potential cause for thyrotoxicosis. Conclusion: ICI induced thyroid disease is not an uncommon condition. It could present as either thyrotoxicosis or hypothyroidism. Both patient and clinician should be aware of potential signs and symptoms of thyroid storm for early recognition and timely treatment of this life-threatening condition. [1] Byun DJ et al.Nat Rev Endocrinol. 2017 Apr;13(4):195-207 [2] Iyer PC et al. Thyroid. 2018 Oct;28(10):1243-1251 [3] Endocr Relat Cancer. 2014 Mar 7;21(2):371-81 [4] Puzanov et al. Journal for ImmunoTherapy of Cancer (2017) 5:95