Diabetes insipidus is a lack of antidiuretic hormone (ADH) or a lack of response to ADH. This prevents the kidneys from being able to concentrate the urine leading to polyuria (excessive amounts of urine) and polydipsia (excessive thirst). It can be classified as nephrogenic or cranial.

Primary polydipsia is when the patient has a normally functioning ADH system but they are drinking excessive quantities of water leading to excessive urine production. They don’t have diabetes insipidus.

Nephrogenic Diabetes Insipidus

causes - DIME

Nephrogenic diabetes insipidus is when the collecting ducts of the kidneys do not respond to ADH. It can also be caused by:

• Drugs, particularly lithium used in bipolar affective disorder
• Intrinsic kidney disease
• Mutations in the AVPR2 gene on the X chromosome that codes for the ADH receptor
• Electrolyte disturbance (hypokalaemia and hypercalcaemia)

Cranial Diabetes Insipidus

Cranial diabetes insipidus is when the hypothalamus does not produce ADH for the pituitary gland to secrete. It can be idiopathic, without a clear cause or it can be caused by:

• Brain tumours
• Head injury
• Brain malformations
• Brain infections (meningitis, encephalitis and tuberculosis)
• Brain surgery or radiotherapy
• haemochromatosis

Presentation

• Polyuria (excessive urine production)
• Polydipsia (excessive thirst)