AVP and dentinogenesis imperfecta: The increased fluid retention is unable to suppress both ADH and pituitary resistance resulting in further free water retention.20 There is also increased non-osmotic ADH secretion, from low cardiac output stimulating the carotid baroreceptors.6,21 These mechanisms clearly explain the presentation of oliguria in our patient despite confirmed diagnosis of DI and no response to desmopressin that improved following thyroxine administration.