polydipsia

Polydipsia is excessive thirst accompanied by increased fluid intake, beyond what an individual normally requires. It can be a primary behavioral condition or a sign of an underlying medical disorder. Primary polydipsia (psychogenic polydipsia) refers to thirst driven by behavioral or psychiatric factors. Secondary polydipsia results from conditions that alter fluid balance or osmolality, such as diabetes mellitus, diabetes insipidus (central or nephrogenic), chronic kidney disease, prolonged fever, or certain medications.

The sense of thirst is regulated by hypothalamic osmoreceptors and circulating signals. Antidiuretic hormone (vasopressin) promotes water reabsorption in the kidneys. In primary polydipsia, excessive water intake can suppress vasopressin, producing dilute urine; if intake greatly exceeds the kidneys’ ability to excrete free water, hyponatremia may occur. In diabetes insipidus, insufficient or ineffective vasopressin causes free-water loss and compensatory polydipsia. Secondary polydipsia occurs in the setting of conditions that disrupt fluid balance or cause polyuria, with thirst perceived to correct fluid loss.

Clinical features include persistent, intense thirst and high-volume urine production, often with nocturia. Patients may be asymptomatic aside from thirst; hyponatremia can cause confusion, seizures, or coma in severe cases. The differential diagnosis includes primary polydipsia, central diabetes insipidus, nephrogenic diabetes insipidus, diabetes mellitus, and renal disease.

Evaluation involves history, physical examination, and laboratory testing. Serum sodium and osmolality, urine osmolality, and urine volume help distinguish causes. A water deprivation test with vasopressin administration is commonly used to differentiate primary polydipsia from diabetes insipidus.

Management targets the underlying cause and safety. Primary polydipsia is treated with fluid intake modification and psychiatric or behavioral support. Central diabetes insipidus responds to desmopressin; nephrogenic DI may require salt restriction, hydration, and specific therapies. Diabetes mellitus control and treatment of renal disease are essential where relevant.