What condition is characterized by an excess of ADH?

The condition characterized by an excess of antidiuretic hormone (ADH) is known as the Syndrome of Inappropriate Antidiuretic Hormone (SIADH). This syndrome occurs when there is an abnormal release of ADH from the posterior pituitary gland, which leads to excessive water reabsorption in the kidneys. The result of this overproduction is a dilution of the serum sodium level (hyponatremia) and an increase in total body water, causing the body to retain water and potentially leading to a host of complications, including confusion, seizures, and in severe cases, coma.

In SIADH, the regulation of fluid balance is disrupted, and the clinical manifestations can vary from mild to severe, depending on how rapidly the sodium levels drop. This is different from conditions like diabetes insipidus, where there is insufficient ADH leading to excessive urination and thirst. Diabetes mellitus and hyperglycemia do not involve ADH levels directly; rather, they are typically related to insulin and glucose metabolism. Therefore, SIADH is distinctly identified for its excess ADH and the physiological abnormalities that stem from this condition.