A 50 years okl smoker and hypeensive was diagnose to have non-small cell lung carcinoma with brain metastases. He is on enalapril and hydrochlorothiazide for hypeension. On investigation, he had a serum Sodium 120 mg/dl|, Urinary Sodium ll0 mg/dl, Serum creatinine 0.8 mg/dL, Serum osmolarity 285 mOsm/L, Urinary osmolarity 35l mOsm/L, Urinary K+ 9 mg/dl, Blood sugar ll2 mgldL and BP of 150/90 mm Hg. Which of the following is the mnst probable cause for his hyponatremia?

Answer-C. SIADHHyponatremia is a common electrolyte abnormality in cancer patients, and SIADH is the most common cause among patients with cancer.The term SIADH is applied to conditions with vasopressin excess.Vasopressin excess is termed inappropriate as this increase occurs despite decreased plasma osmolality.Increased vasopressin acts on renal tubules, resulting in increased absorption of water (increased total body water), concentrated urinec and decreasing serum osmolalityEUR and hyponatremiao.Edema does not occur despite increased total body waterg (due to unknown reasons)-Clinical euvolemia