Which condition results from excessive secretion of antidiuretic hormone?

• A. SIADH
• B. Diabetes insipidus
• C. Hyperthyroidism
• D. Cushing syndrome

Answer: (A)

Excessive secretion of antidiuretic hormone causes the body to retain too much water, diluting the blood and lowering serum osmolality. This leads to a pattern known as SIADH, where there is hyponatremia with inappropriately concentrated urine. The kidneys keep reabsorbing water in the collecting ducts because ADH is high, so urine is concentrated (high urine osmolality) while the blood becomes dilute. Patients are often euvolemic or mildly hypervolemic, and symptoms arise from the low sodium—nausea, confusion, and in severe cases seizures or coma.

Diabetes insipidus, by contrast, results from too little ADH or the kidneys not responding to it, causing large volumes of dilute urine and dehydration—opposite of SIADH. Hyperthyroidism and Cushing syndrome are separate endocrine disorders with different underlying mechanisms and do not involve ADH-driven water retention.