From cranial diabetes insipidus to vasopressin deficiency: terminology, tests and treatment.

Many paediatricians assess infants or children with a history of excessive fluid intake. Most patients will have primary polydipsia, but the differential diagnosis includes rare disorders requiring specialist input and lifelong treatment. This article will focus on conditions characterised by abnormal vasopressin (AVP) secretion by the posterior pituitary gland. We describe the clinical features and investigations that are useful in identifying the underlying pathology in these patients and explain why the water deprivation test may not be needed. We discuss why the term diabetes insipidus should be consigned to the history books and why the precise cause of AVP deficiency is still unclear in some instances. Two clinical cases will be used to highlight topics such as diagnostic uncertainty, assessing thirst objectively and the potential role of copeptin.