Diabetes Insipidus

Definition

Diabetes Insipidus (DI) is a disorder characterized by the inability of the kidneys to concentrate urine, resulting in excessive urination (polyuria) and excessive thirst (polydipsia). It is caused either by deficient production of antidiuretic hormone (ADH, central DI) or renal resistance to ADH (nephrogenic DI).

Epidemiology

• Central DI: incidence ~1 per 25,000 population
• Nephrogenic DI is rarer, often genetic or drug-induced
• Can occur at any age; congenital forms present in infancy
• No clear sex predilection

Etiology

• Central DI: idiopathic, pituitary tumors, neurosurgery, trauma, infections, infiltrative diseases
• Nephrogenic DI: genetic mutations (AVPR2, AQP2), drugs (lithium, demeclocycline), chronic kidney disease, electrolyte disturbances

Pathophysiology

• Central DI: decreased ADH production from posterior pituitary → inability to reabsorb water in kidneys
• Nephrogenic DI: kidneys unresponsive to ADH → water loss despite normal or elevated ADH
• Result: hypotonic polyuria, hypernatremia, dehydration if fluid intake is insufficient