MON-063 - Hypopituitarism as the initial clinical manifestation of a primary central nervous system lymphoma (PCNSL) of the hypothalamus

Primary central nervous system lymphoma (PCNSL) rarely involves the hypothalamic-pituitary region and may present with endocrine and hypothalamic dysfunction before definitive tissue diagnosis. We report a 67-year-old woman with primary hypothyroidism on levothyroxine and prior radiosurgery for a trigeminal schwannoma who developed polyphagia, 8-kg weight gain, somnolence, short-term memory loss, postural instability, and gait difficulty, followed by polyuria, polydipsia, headache, diplopia, and fluctuating hypertension and hypotension. She presented with excessive somnolence, generalized weakness, confusion, dizziness, arterial hypotension, and loss of consciousness; blood pressure was 90/60 mmHg and she was dehydrated and stuporous. Serum sodium was 165 mEq/L with polyuria, consistent with arginine-vasopressin deficiency, and desmopressin plus hypotonic solutions decreased urinary output. Hormonal evaluation showed growth hormone deficiency, hypothyroidism, hypogonadism, hyperprolactinemia, and central adrenal insufficiency, with IGF-1 25.1 ng/mL, GH 0.06 ng/mL, estradiol 9.32 pg/mL, LH 0.3 IU/L, FSH 1.01 IU/L, prolactin 121 ng/mL, ACTH 1.00 pmol/L, cortisol 5.81 ug/dL, TSH 0.45 IU/L, free T4 0.62 ng/dL, total T3 60.1 ng/dL, and free T3 1.85 pg/mL. HIV testing was negative, and aside from discrete leukopenia and mild normochromic hypochromic anemia there was no evidence of altered immune response. Brain MRI showed multiple infiltrative lesions involving the hypothalamus, infundibulum, optic chiasm, corpus callosum, pontine tegmentum, septum pellucidum with fornix extension, mammillary bodies, and both thalami, with subsequent enlargement of the lateral and third ventricles. A ventriculoperitoneal shunt and biopsy of the most accessible lesion were performed; dexamethasone 8 mg intravenously every 8 hours was followed by clinical improvement and significant radiologic lesion reduction within 15 days. Histopathology demonstrated diffuse large B-cell lymphoma of the CNS with CD20 positivity in 100% of cells, CD3 negativity, Ki67 15%, CD30 negativity, CD56 negativity, and SALL4 negativity. Hematology found no extra-neurological tumor activity. Treatment with methotrexate, high-dose cytarabine, thiotepa, and rituximab was initiated; three of four planned cycles were completed with adequate tolerance and response, with full neurologic recovery and improved blood pressure control. This case highlights that anterior pituitary dysfunction plus arginine-vasopressin deficiency, severe hypernatremia, and hypothalamic-infundibular infiltrative lesions should prompt urgent evaluation for PCNSL, a rare but important cause of hypothalamic-pituitary dysfunction. Recognition is critical because tissue diagnosis established the etiology and corticosteroid therapy was followed by marked lesion reduction.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*