SAT-245 A Rare Case of Clival Primary Diffuse Large B-Cell Lymphoma Presenting with Panhypopituitarism and Unmasked Diabetes Insipidus

Background: Central adrenal insufficiency (AI) is known to conceal diabetes insipidus (DI) by impairing free water clearance from the renal system and inhibiting polyuria, which is later unmasked by the initiation of glucocorticoids. The instances of masked DI in the literature are confined to case reports - the actual incidence is unclear. There have been no documented cases of masked DI secondary to a clival tumor, which remains a rare cause of hypopituitarism. Here we discuss a case of primary diffuse large B-cell lymphoma (DLBCL) of the clivus presenting with panhypopituitarism and the development of DI upon glucocorticoid initiation. Clinical Case: A 60-year-old man with DLBCL initially presented to an outside institution with headache, diplopia, and right eye ptosis. Brain MRI showed enhancement of the clivus without obvious pituitary gland involvement. He underwent biopsy with partial resection of the tumor and pathology confirmed DLBCL. His course was complicated by persistent fevers. Extensive work-up was unrevealing and he was transferred to our institution for further management. On admission, infectious work-up was positive for C. Difficile. He later developed septic shock requiring vasopressors and broad-spectrum antibiotics. Despite prolonged antibiotics, he remained hypotensive. Due to proximity of the clivus and sella, there was concern for pituitary involvement. A random cortisol was 9.1 [3.7-19.4 ug/dL], subsequent 250ug cosyntropin stimulation test yielded 13.1 and 14.9 at 30- and 60-minutes, respectively. Given inadequate stimulation and persistent hypotension in this critically ill patient, he was then started on stress dose hydrocortisone (HC) with prompt resolution of hypotension. Further work-up of the pituitary axes was consistent with anterior hypopituitarism: ACTH 5 [6-50 pg/mL], TSH 0.336 [0.350-4.940 uIU/mL], free T4 0.5 [0.7-1.5 ng/dL], FSH 0.3/LH 0.1 [1-10 mIU/mL], IGF-1 <16 [41-279 ng/mL], prolactin <1 [3-16 ng/mL]. On day two of HC stress dosing, he developed hypernatremia and polyuria. Urine studies were consistent with DI and desmopressin was started with subsequent improvement. Conclusion:This is the first documented case of DLBCL of the clivus leading to panhypopituitarism. For tumors in close proximity to the pituitary, there should be a low threshold for pituitary axes evaluation. In addition, masked DI from central AI remains rare and requires close attention by the Endocrinologist following initiation of glucocorticoids.