Diabetes insipidus (DI) is a condition characterized by excessive thirst and excretion of large amounts of severely dilute urine, with reduction of fluid intake having no effect on the concentration of the urine.
There are different types of DI, each with a different set of causes. The most common type in humans is the neurological form, called central DI (CDI), which involves a deficiency of arginine vasopressin (AVP), also known as antidiuretic hormone (ADH). The second common type of DI is nephrogenic diabetes insipidus (NDI), which is due to kidney or nephron dysfunction caused by an insensitivity of the kidneys or nephrons to ADH. DI can also be gestational, or caused by alcohol or some types of drug abuse.

The underlying causes of CDI can include vascular disorders, autoimmune diseases, infection, sarcoidosis, some drugs, surgery, head trauma, benign or metastatic pituitary-hypothalamic tumor (particularly originating from breast and lung), although 50% of cases are found to be idiopathic.

Polyuria (of extremely dilute urine) leads to dehydration and hypernatremia. The significant clinical features relate to cerebral dehydration, which progressively causes lethargy, weakness, irritability, seizures, coma, and death.
The diagnosis is made by the measurement of the serum sodium level and the serum and urine osmolality.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on October 12, 2016.