What happened, in summary

A previously healthy 45-year-old man was hospitalized with severe hyponatremia that caused agitation and personality changes. A chest CT identified a tumor that was diagnosed as small cell lung cancer, and further testing confirmed cancer-related SIADH. His sodium initially required hypertonic saline, a high-salt diet and strict fluid restriction. He was later readmitted for his first course of cisplatin-based chemotherapy, but hyponatremia recurred during treatment. Dietary measures were difficult to sustain and prolonged his hospitalization. Tolvaptan was therefore introduced and adjusted to a maintenance dose that stabilized his sodium. This allowed him to stop the strict diet and fluid restriction, receive later chemotherapy as an outpatient and return to construction work. Four months after starting tolvaptan, brain metastases developed and second-line chemotherapy was started. During that treatment, pelvic metastases caused worsening pain, nausea and loss of appetite. He was hospitalized for third-line chemotherapy and opioid pain control. One month later, treatment shifted to a palliative approach as oral intake became difficult. Tolvaptan was stopped, his hyponatremia worsened, and he died approximately 1 year after the lung cancer diagnosis.