Diabetes insipidus (DI) is not related to diabetes mellitus (T1DM / T2DM), although shares similar signs/symptoms.
DI is a rare condition characterised by the production of large amounts of dilute urine (polyuria) and greatly increased thirst (polydipsia).
DI is caused by a problem with either the production or action of the hormone arginine vasopressin (AVP; also known as anti-diuretic hormone, ADH). Lack/inaction of AVP means the kidneys are unable to retain water.
There are two main forms: central DI (also known as cranial or neurogenic DI), caused by a deficiency of AVP and nephrogenic DI, caused by resistance to AVP in the kidneys (the kidneys do not respond to AVP). DI can also be related to pregnancy (gestational DI) or a problem with the body's thirst mechanism (dipsogenic DI).