SAT437 Immunotherapy Induced Pituitary Apoplexy

Disclosure: A. Uddin: None. M.J. Gardner: None. A. Akofu: None. N. Sheung: None. S. Dejhansathit: None. N. Akabogu: None. F. Marium: None. We present a case of a 42 year old male with past history of metastatic melanoma s/p 3 cycles of ipilimumab and nivolumab immunotherapy that originally was referred to endocrinology due to elevated prolactin of 40 and MRI finding of questionable 6 mm pituitary adenoma. There was not a clear other cause of prolactin elevation. Other notable labs in pituitary hormonal evaluation were elevated FSH of 24 and LH 16 with normal testosterone 663. TSH of 4.3 and FT4 of 1.22. After the 4th cycle of ipilimumab and nivolumab he had a severe headache that was unremitting, he called his oncology nurse line which instructed him to hydrate. He presented for admission to the hospital after coming confused, unsteady on his feet and his headache had already improved. Labs demonstrated severe hyponatremia at 111 with serum osm of 238 and urine osmolality of 504 and specific gravity of 1.012. Brain MRI demonstrated a 1.2 cm pituitary lesion compared to less than 1 month prior, consistent with hypophysitis. Repeat pituitary labs showed hypogonadotropic hypogonadism with total testosterone of 39 and inappropriately normal FSH of 7 and LH of 2, central hypothyroidism with TSH 0.232, FT4 0.70, FT3 1.8, secondary adrenal insufficiency with cosyntropin stimulation test up to cortisol of 16 for partial response and ACTH of 17. Hyponatremia was managed inpatient and he was discharged on appropriate hormone replacement. Subsequent brain MRI with normal pituitary finding without enhancing lesions. Repeat hormonal testing showed persistent hormonal deficiencies with undetectable cortisol and ACTH despite holding hydrocortisone therapies. Prolactin was also tested in the 4-10 range on repeat testing. He continued on nivolumab monotherapy with oncology. This case report details a clear case of immunotherapy treatment leading to destruction of prolactinoma and presentation of pituitary apoplexy given the short time line of 1 month and cycle of therapy between radiographic and hormonal assessment. We hope this case helps bring awareness to the evolving list of conditions to survey for with immunotherapy and suggests a role of identifying prolactinomas biochemically and or radiographically to affect management. It may even suggest a role in treatment for medically refractory pituitary adenomas. Presentation: Saturday, June 17, 2023