Severe hyponatremia in the setting of mediastinal neuroblastoma in an elderly male

Introduction: Neuroblastomas are rare neoplasms with the potential to express paraneoplastic syndromes. Case Report: We report the case of a 77-year-old male with biopsy-confirmed unresectable anterior mediastinal neuroblastoma with symptomatic hyponatremia likely due to paraneoplastic syndrome of inappropriate antidiuretic hormone (SIADH). He had multiple inpatient admissions for symptomatic hyponatremia over the 3-year period that we examined, with a paucity of admissions during chemoreduction with adjuvant radiation therapy. Due to the rarity of this tumor, there is no standard treatment protocol and the literature regarding these neoplasms exists primarily as case reports. Conclusion: This case report adds to the existing literature detailing paraneoplastic SIADH in the setting of mediastinal neuroblastoma in adults and highlights the importance for oncologists to be cognizant of this syndrome as a complication of a particular rare malignancy.