Syndrome of Inappropriate Anti-diuretic Hormone (SIADH) in Non-small Cell Lung Cancer (NSCLC) Following Agent Orange Exposure: A Case Report.

We present the case of a 77-year-old male with a significant smoking history and prior Agent Orange exposure, who was admitted to the hospital multiple times with clinical and laboratory findings consistent with the syndrome of inappropriate anti-diuretic hormone (SIADH). The patient presented to the hospital on multiple occasions with symptoms and laboratory findings supportive of SIADH in the setting of malignancy. During his first visit, imaging studies demonstrated a right-sided pleural effusion, which was drained and sent for cytology and immunohistochemical staining studies. Following correction of his presenting hyponatremia, he was discharged with appropriate medications and follow-ups to discuss pleural fluid results. Three weeks later, he presented with similar symptoms, and the available pathology results of the pleural fluid specimen supported non-small cell lung cancer (NSCLC), likely adenocarcinoma.  This report highlights a rare occurrence of SIADH in the setting of NSCLC and emphasizes the importance of considering atypical paraneoplastic syndrome presentations in patients with multifactorial hyponatremia. It also engages in a discussion of the pathophysiology, clinical presentation, and diagnostic approach to SIADH in the context of NSCLC.