Abstract
Background. Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a disorder of impaired water excretion and hyponatremia by the excess secretion of arginine-vasopressin (AVP). We report a case of refractory SIADH accompanying small cell lung cancer (SCLC), successfully treated with an AVP V2 receptor antagonist, tolvaptan. Case. A 70-year-old man presented with bloody sputum and cough for 4 months, anorexia for 1 month, and dyspnea on effort for 2 weeks. He was diagnosed as SCLC complicated with superior vena cava syndrome and hyponatremia and referred to our hospital. He received chemotherapy with carboplatin and etoposide. His hyponatremia, diagnosed as SIADH, was resistant to the treatments with hypertonic saline and furosemide under fluid restriction for 3 weeks. Therefore, tolvaptan, 7.5 mg qd, was started, resulting in the normalization of serum sodium level in 2 days and the improvement of conscious level. He has experienced no adverse events with tolvaptan therapy, but remains dependent on tolvaptan in spite of the tumor regression. Conclusion. Tolvaptan is an effective therapy to control refractory SIADH accompanying SCLC.
