SUN-064 Arginine Vasopressin Deficiency Post-Thoracic Surgery Associated with Metastatic Breast Cancer

Abstract K.G. Romo: None. M. Koh: None. V. Bonert: None. Arginine vasopressin deficiency (AVP-D) formerly known as central diabetes insipidus is a urinary concentrating defect that manifests as polyuria with compensatory polydipsia. AVP-D can be due to metastatic pituitary lesions, most commonly from breast or lung cancer, and, in rare cases, can follow instrumented spinal fusion. The following presents a 57-year-old-female with stage IV estrogen receptor-positive breast adenocarcinoma, spinal metastases, and spinal epidural tumor complicated by cord compression and pathologic T12 fracture, who acutely developed polyuria and hypernatremia after T10-L2 fusion and T12 tumor decompression. Symptoms included polyuria and increased thirst, without headaches or visual changes. Vital signs were normal aside from intermittent tachycardia. Visual fields were full to confrontation, with normal sensation and strength. Urine output exceeded 300cc/hour for 3 consecutive hours, and a pattern of early morning polyuria occurred for 3 consecutive days under observation. She unequivocally met AVP-D criteria for DDAVP with concurrent serum Na>145 mmol/L (136-145 mmol/L) and urine specific gravity <1.005 (1.002-1.024). MRI pituitary with/without contrast revealed loss of the posterior pituitary bright spot. Epidural tumor pathology confirmed metastatic breast adenocarcinoma. Given the established pattern of morning urine dumping, the patient was started on DDAVP 0.1 mg nightly with subsequent resolution of polyuria and hypernatremia. Possible etiologies of AVP-D include metastatic breast cancer versus instrumented spinal fusion. The timeline of symptoms and hypernatremia occurring acutely after spinal surgery supports the latter etiology, however, epidural pathology noting metastatic breast adenocarcinoma supports possible metastasis from the spinal epidural tumor to the posterior pituitary gland. Furthermore, metastatic pituitary lesions are more likely to occur in the posterior pituitary rather than the anterior pituitary, as vascular supply to the posterior pituitary is from inferior hypophyseal arteries compared to the hypothalamic/pituitary portal supply into the anterior pituitary gland. An embolic metastatic lesion may have occurred during spinal fusion and decompression of the epidural tumor. This case presents a rare instance of AVP-D associated with metastatic breast cancer and post-spinal surgery. Increased reporting of similar cases may elucidate the mechanisms of AVP-D in this scenario. Sunday, June 2, 2024