A 60-year-old man with small cell carcinoma of lung is rushed to emergency room in coma after suffering a clonic-tonic seizure. Patient's temperature is 37degC , blood pressure 100/50 mm Hg and pulse is 88 per minute. Laboratory studies show a serum sodium of 103 mmol/L, normal serum levels of BUN & creatinine and a dilute but otherwise normal urine. A CT scan of the head is normal. Which of the following is the most likely cause of seizures in this patient?
Central diabetes insipidus Diabetes mellitus Renal metastases Syndrome of inappropriate ADH secretion