Diabetes Insipidus

Key points

• Diabetes insipidus (DI) causes excessive dilute urine because of either deficient ADH/vasopressin secretion (central/cranial DI) or renal resistance to ADH (nephrogenic DI) . The current term diabetes insipidus remains clinically useful; AVP-deficiency/AVP-resistance terminology is increasingly used.
• Head injury can cause central DI, particularly when the hypothalamic–pituitary axis is damaged.
• Pituitary or hypothalamic surgery can cause central DI.
• Craniopharyngioma and other hypothalamic/pituitary lesions can cause central DI.
• Other causes of central DI include infiltrative/inflammatory disease, malignancy and genetic disorders; nephrogenic DI is classically caused by lithium, hypercalcaemia, hypokalaemia and certain renal/drug-related disorders.
• DIDMOAD (Wolfram syndrome) is the association of diabetes insipidus, diabetes mellitus, optic atrophy and deafness; it is a rare genetic syndrome.
• MRCP discriminator: central DI → responds to desmopressin; nephrogenic DI → little/no response. Hypernatraemia + very dilute urine is the classic untreated pattern.
• Nephrogenic DI trap: lithium is the classic drug cause.