What is central diabetes insipidus?

What are the causes and symptoms of central diabetes insipidus? 

Diabetes insipidus results from a deficiency of or insensitivity to the antidiuretic hormone vasopressin.

When the body is functioning optimally, vasopressin is produced by the hypothalamus and then stored in the pituitary gland, both parts of the brain. It is then released into the body to regulate water levels. By acting on the kidneys, it prevents water from being eliminated with the urine, thereby helping to cover the body's water requirements.

In diabetes insipidus, vasopressin is unable to play its role as an antidiuretic agent. Water is therefore eliminated in excessive quantities.

Diabetes insipidus manifests itself either abruptly or progresses rapidly as a significant, permanent increase in the volume of urine (polyuria). The volume of urine can reach 2.1 to 2.6 gallons a day., and in the most severe cases it can be up to 5 gallons a day. It is pale like water and contains no pathological elements: no sugar or albumin.

Polyuria is accompanied by polydipsia. Patients are always thirsty, permanently and insatiably. They drink enormously (between 3 and 30 litres a day), non-stop, day and night, but are unable to quench their thirst.

Apart from these symptoms, the patient is in good general condition, except when hyper-hydrated (nausea, headaches) or dehydrated.

Diabetes insipidus may be congenital (present from birth), acquired (due to external factors) or idiopathic (with no known cause).

The following causes have been identified to date:

• Cranial trauma or cerebral lesions,
  
• Neurosurgical intervention in the hypothalamic-pituitary region,
  
• Vascular lesions such as aneurysms or thrombosis,
  
• Brain tumors,
  
• Nervous system infections such as encephalitis and meningitis,
  
• Tuberculosis,
  
• Sarcoidosis,
  
• Polycystic kidney disease (cysts in the kidneys)...
  

Idiopathic diabetes insipidus appears at any age, but particularly between the ages of 10 and 20. In the case of congenital form, it can appear as early as the neonatal period.

How can central diabetes insipidus be diagnosed? 

Diabetes insipidus is suspected when there is a significant increase in the volume of urine associated with intense thirst.

Diagnosis can be confirmed by the following tests:

Water restriction test

This test is used to determine whether ADH hormone (vasopressin) can still be secreted.

The water restriction test is carried out in hospital to be able to act quickly in case of possible dehydration. The patient needs to be fasting from the day before.

Every 15 minutes, the patient is weighed and their blood pressure is taken, and every 30 minutes their urine is collected in numbered jars.

The test lasts 8 hours, but can also be stopped when the patient shows signs of discomfort (anxiety, rapid pulse, dry mucous membranes, drop in blood pressure, etc.).

Thus, the combination of dehydration and the kidney's inability to concentrate urine despite not consuming beverages confirms the diagnosis.

In the case of real diabetes insipidus, the water restriction test cannot be completed.

This test is used to identify ADH (vasopressin) deficiency.

Urine tests 

These are used to check for the presence of sugar in the urine - a sign of diabetes mellitus.

Blood tests 

Among other things, these tests can identify whether there is a high concentration of sodium in the body.

Finally, if the causes of diabetes insipidus are known, magnetic resonance imaging is the fundamental test for confirming the cause.

What are the treatments of central diabetes insipidus? 

Treatment of diabetes insipidus obviously depends on the cause. In all cases, the patient must not be allowed to become dehydrated or over-hydrated.

Desmopressin (DDAVP®) is an analogue of ADH (vasopressin) with a powerful antidiuretic action. It acts in the same way as the natural hormone, but the effect lasts longer. These treatments are generally administered orally, in the form of a nasal spray or intravenously, once or several times a day.

The doses are adjusted to maintain the body's water balance and normal urine production. An overdose of vasopressin may lead to fluid retention, edema or other more serious disorders.

Diabetes insipidus can sometimes be controlled by drugs that stimulate vasopressin production, such as carbamazepine (Carbatrol®, Epitol®, etc) and other diuretics. However, these treatments are not sufficient to control severe diabetes insipidus.