LBSAT236 A Case of Immune Checkpoint Inhibitor Pembrolizumab Induced Simultaneous Rare Endocrinopathies, Type 1 DM (presenting As DKA) And Grave's Thyrotoxicosis, With Evidence Of Autoimmunity Development.

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Abstract Introduction Pembrolizumab is a novel immunotherapeutic monoclonal antibody directed against PD-1 (programmed death receptor 1), which has been linked to endocrinopathies. We present a rare case of type 1 DM and Grave's disease noted in setting of Pembrolizumab use. Case presentation A 56 year old female with history of Hodgkin's lymphoma (being treated with Pembrolizumab), heart failure and type 2 DM was sent to the ED from oncology infusion clinic for labs concerning for DKA. She endorsed fatigue, light-headedness, polydipsia and polyuria. She had moderate to severe DKA with bicarbonate 9 mmol/L (22 - 31), anion gap 29 mmol/L (7 -17), venous Ph 7.16 (7.30 - 7.40), beta hydroxybutyrate 9.4 mmol/L (0 - 0.3) and blood glucose 451 mg/dL (70 - 100). She was admitted to the ICU and started on insulin drip. She had a 20 year history of type 2 DM and prior to this episode had been managed on Metformin 500 mg daily alone with good glycemic control (HbA1c 5.7 - 7.1%) and had never had DKA before. Of note, she also reported recent 75 pound weight loss which she attributed to lifestyle changes. GAD65 antibody assay was positive 5.49 nmol/L (<=0. 02 nmol/L). She was discharged on a basal bolus insulin regimen and continues to follow up with Endocrinology. On admission, she had thyrotoxicosis with TSH 0. 06 uIU/mL (0.50 - 5.70), fT4 1.8 ng/dL (0.9 - 1.7), and total T3 99 ng/dL (80 -200) while clinically euthyroid. Repeat TFTs in one week were consistent. TSI was elevated 1.8 (<=1.3 TSI Index). 10 days later, labs showed improvement TSH 0. 09 uIU/mL, fT4 1.2 ng/dL and total T3 130 ng/dL. As she was clinically euthyroid and noted to have improving levels, she was managed conservatively. However, one additional one month later, tests were repeated and showed progression to hypothyroid state - TSH 44.23 uIU/mL and fT4 0.4 ng/dL. She was started on Levothyroxine supplementation. Repeat testing showed normalization of TSH. Discussion Our patient had long standing history of well controlled Type 2 DM and no history of thyroid abnormalities yet presented with moderate to severe DKA and thyrotoxicosis due to Grave's disease shortly after initiating immune checkpoint inhibitor therapy. GAD65 antibody and TSI panel were positive indicating development of autoimmunity. Although rare, development of rare endocrinopathies such as insulin deficient diabetes and Grave's disease are important side effects of immunotherapy. Patients being treated with immunotherapeutic agents should be monitored closely with serial metabolic panel testing for the first twelve weeks after starting therapy. In addition, a low threshold should be maintained for testing for additional thyroid related endocrinopathies. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

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