What happened, in summary

An 88-year-old man was admitted for evaluation of a pleural effusion and was found to have mild hyponatremia. Testing showed persistent inappropriate antidiuretic hormone activity, and he was subsequently diagnosed with small cell lung cancer complicated by cancer-related SIADH. Because of his advanced age, best supportive care was selected rather than anticancer chemotherapy. Managing the low sodium became an important part of his care. A high-salt diet and strict fluid restriction were difficult for him to follow and did not reliably prevent recurrent hyponatremia. Low-dose tolvaptan was therefore started and stabilized his sodium within about 10 days. He was later hospitalized again as the pleural effusion increased and he developed nausea and poor appetite. After discharge, he stopped taking tolvaptan. During a third hospitalization for worsening respiratory distress and appetite loss, his hyponatremia again became more severe. At that point, care shifted to a palliative approach. He later died of carcinomatous lymphangitis. Tolvaptan helped stabilize his sodium and reduced the burden of strict dietary and fluid restrictions while his lung cancer was managed with supportive rather than cancer-directed care.