The causes of diabetes insipidus are very different than the causes of diabetes mellitus and even though they share two common symptoms, which are increased thirst and increased urination, they are two entirely unique diseases.
Causes of diabetes insipidus are most commonly related to a deficiency of antidiuretic hormone (ADH), also known as arginine vasopressin (AVP) or vasopressin. Diabetes mellitus is a condition related to high blood sugar levels caused by too little production of insulin or a failure of the body cells to respond properly to insulin.
To better understand the causes of diabetes insipidus, it helps to understand more about how urine output and thirst are influenced. Urine production is regulated by the hypothalamus, which produces ADH. This hormone is then transported to the pituitary gland where it is stored until needed. The hypothalamus also regulates thirst.
Your kidneys balance fluids in your body and are influenced by ADH. For instance, if ADH is inhibited or deficient your kidneys will release more urine.
There are 4 types of diabetes insipidus and the causes of diabetes insipidus are different for each type.
"Vasopressin acts to increases the volume of blood (intravascularly) and, decreases the volume of urine produced therefore a lack of it causes increased urine production and dehydration"(1).
Approximately 25 percent of neurogenic diabetes insipidus cases are due to unknown causes. It may be caused by damage to the pituitary gland as a result of a tumor, trauma, neurosurgery or other rare causes. In rare cases this type is due to an inherited mutation of a gene.
(1) Wikipedia (2010). Neurogenic diabetes insipidus. Retrieved from http://en.wikipedia.org/wiki/Neurogenic_diabetes_insipidus