Acute hyponatremia from immune checkpoint inhibitor therapy for non–small cell lung cancer

A 52-year-old Caucasian woman on pembrolizumab maintenance after induction with chemotherapy (carboplatin, pemetrexed) and pembrolizumab for stage 4 non–small cell lung cancer was admitted with increasing weakness. She had presented to emergency with similar complaints 2 weeks earlier, and she was hydrated with normal saline and sent home on antibiotics for urinary tract infection. She reported worsening weakness, anorexia and weight loss of 12 pounds over 3 months. Her other medical problems include chronic pain and depression. Home medications listed at admission were methocarbamol and lorazepam. Vital signs at admission revealed a blood pressure of 105/63 mm Hg and a pulse of 73/min, and pulse oximetry showed 98% saturation on room air. Physical evaluation was normal other than cachexia. Labs revealed low sodium …