Diabetes insipidus

Typical symptoms of diabetes insipidus are:

• a constant feeling of extreme thirst
• frequent urination with pale or colorless urine
• nighttime urination which can cause sleep disorders 

With some types of diabetes insipidus these symptoms occur very suddenly, while with others they develop over months or years.

Other symptoms that indicate a lack of water in the body are, for example:

• weakness and tiredness
• physical and mental lethargy
• muscle aches

Various mechanisms regulate the body’s water levels. The antidiuretic hormone (ADH), also called vasopressin, plays a vital role in this. It is produced in the brain and the pituitary gland releases it to the blood when needed. ADH ensures that the collecting ducts in the kidneys retrieve water from the urine.

When ADH is not produced in sufficient quantities in the brain, or not produced at all, fluids are lost because the kidneys cannot retrieve the water – large volumes of watery, colorless urine are then produced. These cases are known as central diabetes insipidus because the cause of the ADH deficiency lies in the brain and, thus, the central nervous system.

An ADH deficiency often occurs without the exact cause being identified. The inadequate hormone production can sometimes be traced to particular illnesses and risk factors. These include, for example:

• serious head injuries and neurosurgical interventions
• inflammations in the pituitary gland area: it is thought that autoimmune processes often play a role. These immune system disorders involve the body’s own cells being attacked.
• head and brain tumors
• hereditary causes

As well as central diabetes insipidus there is also the so-called renal or nephrogenic diabetes insipidus. In these cases, there is enough ADH in the body but the kidneys are unable to respond adequately to the hormone.

The possible causes of this include:

• hereditary signal transmission disorders: the ADH hormone normally transmits signals to the kidney cells to retrieve water. For hereditary reasons, this process is disturbed.
• certain medications: for example a therapy using lithium for mental illnesses.
• kidney diseases.
• mineral balance disorders: for example, too little potassium or too much calcium in the blood.

Diabetes insipidus can be identified from the typical symptoms and through various laboratory tests.

Measuring urine volume

There is excessive urine production and, therefore, an indication of diabetes insipidus in an adult if over 40 to 50 milliliters of urine per kilogram bodyweight are excreted within 24 hours. That would be over 2.8 to 3.5 liters for a bodyweight of 70 kilograms.

Blood and urine tests

With diabetes insipidus, the blood plasma is typically too concentrated, while the urine is too thinned. This can easily be proven in the lab. It is also important to test the salts (electrolytes) in the blood in order to identify any possible mineral balance disorders.

Measuring the blood sugar level

If the sugar level in the blood and urine is elevated, this usually indicates that it is not diabetes insipidus.

Four special tests are also used:

Thirst test

The patient is deprived of all fluids for several hours. If diabetes insipidus is present, large volumes of less concentrated urine continue to be produced. To avoid complications, the thirst test is monitored by a medical professional.

Desmopressin test

The hormone desmopressin is usually administered in the second part of the thirst test. It works in the same way as the body’s own antidiuretic hormone (ADH). It enables doctors to see which type of condition is involved: if the urine volume and concentration becomes normal when desmopressin is given, it shows that the kidneys are working normally. Therefore the condition is being caused by deficient ADH production in the brain (central diabetes insipidus). On the other hand, if desmopressin has little or no effect, the disorder is in the kidneys themselves (renal diabetes insipidus).

Evidence of copeptin in the blood

This protein plays a role in producing ADH in the brain and may also be an indication of diabetes insipidus.

Magnetic resonance imaging (MRI)

This can detect, for example, inflammations or tumors in the pituitary gland area.

Diabetes insipidus is a rare condition in which large amounts of urine are excreted. The body keeps losing water via the kidneys, which causes extreme thirst.

The kidneys usually produce concentrated urine by recovering water from the urine and thereby avoiding unnecessary fluid loss. This requires a hormone from the pituitary gland (hypophysis), the so-called antidiuretic hormone (ADH), also known as vasopressin. If this is not produced in sufficient quantities, or if the kidneys do not respond correctly to it, diabetes insipidus occurs.

With diabetes insipidus, basically, it is important to drink a lot. In children and older people in particular, a lack of water can quickly cause circulatory failure.

Sometimes a particular cause of diabetes insipidus can be identified and eliminated. For example if there is a disorder in the mineral balance, this can be remedied. Also after medication that can cause diabetes insipidus is withdrawn, the kidney function sometimes recovers. The treatment also depends on the nature of the condition.

Treating central diabetes insipidus

The hormone desmopressin is administered to compensate for the deficient ADH production in the brain. Desmopressin comes as a solution to be injected, as a nasal spray, or in tablet form. 

Treating renal diabetes insipidus

If the diabetes insipidus is being caused by kidney damage, it is important that the diet is low in salts and proteins. Drugs are also used. Some adults can also offset a mild case of diabetes insipidus by drinking a lot. In infants, early treatment is important because a recurring water deficiency can cause substantial development disorders.