The most common cause of euvolemic hyponatremia is which of the following?: (A) Hypothyroidism, (B) Hypoadrenalism, (C) Hypehyroidism, (D) SIADH
Answer is D. The syndrome of inappropriate antidiuresis is the most common cause of euvolemic hyponatremia. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 345