FRI308 A Rare Case Of Plurimorphous Plurihormonal Pituitary Neuroendocrine Tumor With LH Hypersecretion

Disclosure: A. Jeevananthan: None. L. Gratian: None. Background: Plurimorphous plurihormonal pituitary neuroendocrine tumors (PitNETs) are very rare pituitary tumors that are composed of multiple adenohypophyseal lineages and are associated with high risk of recurrence. Further, gonadotropin excess is exceptionally rare. Here we report a rare case of a plurimorphous plurihormonal PitNET with functional hypersecretion of LH. Clinical Case: A 48-year-old male was incidentally found to have a 13x12x14mm pituitary tumor without evidence of cavernous sinus invasion or mass effect during sinus imaging for workup of chronic sinusitis with polyps. Clinical symptoms at the time were notable for night sweats, hot flashes and 1 year history of erectile dysfunction. Functional testing showed normal prolactin, GH, cortisol, and thyroid hormone production. However, LH was elevated at 10.2 mIU/mL (normal range 1.4-7.77 mIU/mL) and FSH was low at 1.3 mIU/mL (normal range 2.5-17.7 mIU/mL) with normal total testosterone of 565 ng/dL (normal range 240-950 ng/dL) but elevated free testosterone of 22 ng/dL (normal range 4.26-16.4 ng/dL). Interval imaging 17 months later showed an increase in size to 16x16x13mm with deviation of the infundibulum to the left and mild mass effect on the optic chiasm. Thereafter, the patient underwent transsphenoidal surgery with subsequent normalization of FSH to 6.2 mIU/mL and LH to 7.9 mIU/mL. Initial post-operative total testosterone level was low at 29 ng/dL but improved spontaneously to 170 ng/dL six weeks following surgery. Pathology was notable for immunohistochemistry (IHC) that showed SF1 lineage (IHC positive for LH, negative for FSH) and PIT1 lineage (IHC positive for prolactin, rare GH). To our knowledge, this is the first reported case of functional LH hypersecretion due to a plurimorphous plurihormonal PitNET. Conclusion: This case aims to shed light on the first noted case of LH only secreting plurimorphous plurihormonal PitNET. Plurihomonal PitNETs are associated with aggressive course and recurrence. Particularly, this case highlights the need for routine use of immunohistochemical staining for accurate diagnosis of PitNETs to ensure rigorous follow-up. Presentation: Friday, June 16, 2023