MON-113 Primary CNS B-Cell Lymphoma Presenting as Panhypopituitarism

Abstract Disclosure: C. Nieves: None. J.S. Subauste: None. Background/Objective: To raise awareness that, although rare, Primary Central Nervous System (CNS) B-Cell Lymphoma may present as panhypopituitarism as the initial presentation. Case report: A 68-year-old male with initial altered mental status, vomiting and polyuria was found to have severe hypernatremia with a sodium level of 166; he was diagnosed with Arginine Vasopressin Deficiency and was started on desmopressin. Pituitary biochemical workup performed was consistent with panhypopituitarism; he was started stress dose steroids and levothyroxine. Head CT scan without contrast showed no intracranial hemorrhage, but a 1.7 x 2.8 x 1.5 cm mass in the hypothalamus. Brain MRI revealed several avidly enhancing involving the optic chiasm/hypothalamus, body of the corpus callosum/ependyma of the left lateral ventricle, and cerebellar hemispheres along the posterior margin of the fourth ventricle with extension into the left medulla. This combination of findings was suggestive of lymphoma vs inflammatory/infectious etiologies. Lumbar puncture was performed with flow cytometry analysis showing no evidence of any B cell lymphoma, but analysis was limited by small sample size. Neurosurgical evaluation with Endoscopic Third Ventriculostomy (ETV) with biopsy yields a final diagnosis of large B-cell lymphoma. Metastatic workup was negative and no evidence of lymphoma outside CNS was found. Discussion: Panhypopituitarism is caused by benign pituitary tumors in 60% of cases. Among different causes of hypopituitarism, arginine vasopressin deficiency at presentation suggests inflammatory/granulomatous process or tumors including metastasis. CNS large B-cell lymphoma presenting as panhypopituitarism is extremely rare. Primary CNS large B-cell lymphoma associated with panhypopituitarism has been reported in fewer than 20 cases in the literature. Conclusion: A detrimental diagnosis like primary CNS malignancy deserves a prompt diagnosis. When evaluating the possible etiologies for panhypopituitarism consider Large B-cell lymphoma, as a culprit. Presentation: Monday, July 14, 2025