MON-425 SIADH with Epistaxis: Rule out Esthesioneuroblastoma

Background: Esthesioneuroblastoma (ENB) is a rare cancer that arises from the olfactory epithelium. Paraneoplastic syndromes may develop from the tumor’s ectopic production of hormonally active substances such as adrenocorticotropic hormone (ACTH), parathyroid hormone-related peptide (PTHrP), and arginine vasopressin (AVP). Here we describe a case of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in a patient with ENB. Case Presentation: A 40-year-old male with a past history of acute lymphoblastic leukemia as a child presented to the ED after 4 wks of intermittent left-sided epistaxis and nasal obstruction. MRI showed an enhancing mass in the left upper nasal cavity with extension into the ethmoid and sphenoid sinuses. Initial labs revealed serum [Na(+)]=129 mmol/L and subsequent work-up was consistent with SIADH: plasma osmolality=281 mOsm/kg, urine osmolality=479 mOsm/kg, and urine [Na(+)]=46 mmol/L. A random serum cortisol was undetectable, raising concern of adrenal insufficiency (AI). An ACTH stimulation test showed a peak cortisol of 15.3 mcg/dL at 60 min; without other signs or symptoms of AI, we decided to monitor the patient off steroids. He was placed on a fluid restriction of 1.0 L/d with improvement of serum [Na(+)] into the normal range. A later repeat ACTH stimulation test revealed a peak cortisol of 19.1 mcg/dL at 60 min, and we determined that his undetectable serum cortisol was secondary to administration of high-dose dexamethasone prior to biopsy of the nasal mass. Biopsy of the mass revealed a malignancy that stained positive for synaptophysin, chromogranin, NSE, CD56, and MDM2 consistent with ENB. PET/CT revealed uptake in the primary tumor mass and bilateral cervical lymph nodes. The patient underwent tumor resection and bilateral neck dissection, followed by adjuvant radiation and chemotherapy for metastatic disease. Serum [Na(+)] levels normalized after resection of the ENB, and the patient remained eunatremic without fluid restriction throughout his treatment with radiation and chemotherapy. Conclusions: Nasopharyngeal carcinoma, including ENB, should be suspected in younger patients who present with SIADH, especially in the setting of epistaxis. Our patient was diagnosed soon after presentation via imaging of the sinuses. However, diagnosis may be delayed in patients who are otherwise asymptomatic. Other endocrinopathies such as AI should be ruled out as causes of hyponatremia, but in younger patients SIADH should be considered to be due to a tumor until proven otherwise. Head and neck tumors are the second most common tumors associated with SIADH after lung tumors. Fluid restriction is an appropriate initial treatment for patients with mild hyponatremia. As in our case, hyponatremia and SIADH usually resolve soon after tumor resection. Serum [Na(+)] should be monitored following tumor resection as a biomarker of possible recurrence of ENB.