6937 A Rare Case of Pembrolizumab-induced Multiple Endocrinopathies Presenting with Acute Adrenal Crisis Secondary to Isolated ACTH Deficiency - A Case Report

Abstract Disclosure: R. Abdelmasih: None. W. Pan: None. Introduction: Pembrolizumab is an immune checkpoint inhibitor (ICI) that blocks programmed cell death receptor 1 (PD-1) which took a massive leap in the oncology world. However, we are still understanding more about its immune-related adverse events (irAEs). Here we report a case of adrenal crisis due to pembrolizumab-induced hypophysitis and adrenalitis. Case Description: A 74-year-old male with a history of left renal cell carcinoma post left nephrectomy 5 years ago, complicated with lung metastasis for which Pembrolizumab was started. 5 months after, patient developed hypothyroidism and was started on Levothyroxine. 3 months later, Patient presented with lethargy and hypotension. Physical exam revealed hypotension (MAP of 55), fever, and acute encephalopathy. AM cortisol 4.2 ug/dL, Patient was started on IV pressors and a stress dose of Hydrocortisone. Hemodynamics improved, and Hydrocortisone was tapered down. ACTH stimulation test revealed a subnormal response of cortisol 0.2, 1.7, and 2.7 ug/dL at 0, 30, and 60 minutes respectively in the setting of very low ACTH of < 1.5 pg/ml, other pituitary hormones were checked, revealing normal insulin-like growth factor was 116 ng/mL, LH 15.29 mIU/mL, and FSH 27.45 mIU/mL. TSH was high 15 mIU/mL and free T4 was 1.4 ng/dl, levothyroxine dose was increased, and hydrocortisone was maintained at 10 in am and 5 in pm with excellent response. Discussion:ICIs inhibit the immunological pathways that control T-cell activation, leading to multiple immune-related endocrinopathies. Thyroiditis is the most reported one (30%), though anti-PD1-induced hypophysitis is exceptionally rare (< 1%). To date, the pathophysiology of pembrolizumab-induced central AI is not clearly understood, it’s presumed that it causes lymphocytic hypophysitis often presenting with isolated ACTH deficiency. Also, Pembrolizumab-induced primary adrenal insufficiency has seldom been reported and not yet understood, interestingly, anti-steroidogenic enzyme antibodies were absent in those few most reported cases which suggests a different mechanism compared to traditional primary AI. We suggest that our patient had combined primary and secondary adrenal insufficiency based on ACTH stim test result with very low cortisol responses in the setting of very low ACTH, which we believe is what led to such severe presentation of adrenal crisis. Diagnosis of PD1-induced AI can be challenging due to the overlapping of advanced malignancy and AI presentation. A higher level of suspicion is prompted especially in patients who experienced other endocrine irAEs (as our patient who had PDL-1-induced hypothyroidism). We present this case to shed light on this rare yet potentially fatal endocrine adverse event that can be reversed by prompt diagnosis and timely management due to the increasing use of pembrolizumab. More cases are needed for a better understanding of such a rare adverse event. Presentation: 6/2/2024