Diabetes Insipidus is a chronic condition characterized by frequent passing out of lots of very dilute urine. It is also characterized by frequent thirst since the individual affected passes out urine often. It has been noted that such individuals usually pass more than 3L of urine in a day and their urine has an osmolarity of less than 300 mOsm/kg.
There is a hormone in the body called Antidiuretic Hormone (Vasopressin) which is responsible for reabsorption of water from the urine when necessary before it finally leaves the body. It is therefore essential to maintain a balance between the volume of fluids in blood and urine (fluid homeostasis).
Diabetes insipidus results when there is little to no Vasopressin or when the collecting duct of the kidney does not respond to this hormone. As such the body is not able to regulate the amounts of fluids. There is therefore loss of excess water in urine even when the body needs the water.
It is worth noting that diabetes insipidus is a rare condition and in no way related to commonly occurring diabetes mellitus. Notwithstanding, both conditions may present with a few similar symptoms. The two most common symptoms in both cases are polyuria (frequent urination) and polydipsia (excessive thirst).
Symptoms of diabetes insipidus
As mentioned earlier, diabetes insipidus results in excessive urination of about 3L of urine in a day. In fact, one can urinate up to about 30 liters in a day. The passage of such copious amounts of urine therefore results in excessive thirst.
Also, through the excessive loss of water from the body, you may become very weak, dehydrated, tired and irritable.
The passage of frequent urine can also disturb your sleep and affect your quality of life.
If you are not able to replenish the lost fluids with adequate amounts, then dehydration may result in a decrease in blood volume, cause hypotension and eventually lead to a deadly shock.
What causes diabetes insipidus?
There are two main types of diabetes insipidus and each of them has its characteristic cause. The two types are:
- Central diabetes insipidus
- Nephrogenic diabetes insipidus
Central Diabetes Insipidus
This is caused by damage to the pituitary gland or hypothalamus in the brain. The antidiuretic hormone (vasopressin) is synthesized in the hypothalamus and stored in the pituitary gland. In the case of thirst, signals are sent to the pituitary gland to release the stored vasopressin which will then act on the kidneys to help reabsorb water from the urine to keep the body hydrated.
Central diabetes insipidus therefore develops when there is a problem with the production, storage or release of the hormone vasopressin.
Some specific cases that may lead to a central diabetes insipidus include:
- Brain tumors
- Autoimmune destruction of the hypothalamus
- Head injuries
- Aftermath of some brain surgeries
- Encephalitis or meningitis (infections of the brain)
Nephrogenic Diabetes Insipidus
This occurs in the presence of the hormone vasopressin but is such that the kidney tissues become unresponsive to its action. So, no water is reabsorbed at the collecting duct of the kidneys even though vasopressin is present.
This can be as a result of:
- A genetic disorder which was inherited
- A long standing kidney problem
- The use of certain medications (example: lithium, antivirals like foscarnet, etc)
Who is likely to get diabetes insipidus
This condition is a very rare condition and may affect people of all ages. The proportion of males affected is equivalent to that of females. However, between the two main types of diabetes insipidus, the central one is the prevalent one (most common).
How is diabetes insipidus diagnosed?
When you present with symptoms related to diabetes insipidus, your doctor is likely to screen you for diabetes mellitus since it presents with similar symptoms and is the most commonly occuring between the two.
Once diabetes mellitus has been ruled out, your doctor may then order tests that may be specific for diabetes insipidus. Some of these tests include:
- Water deprivation test:
As a normal human being not having diabetes insipidus, your frequency of urination and volume of urine will go down drastically if you are deprived of water for a while. However, people with diabetes insipidus keep producing copious dilute urine even after being water deprived for about 12 hours.
This test is therefore based on that principle. You are deprived of water for about 12 hours. Within those 12 hours, your doctor will intermittently monitor you for the frequency of urination, volume of urine passed, weight loss, blood pressure, and heart rate.
If within the period of observation, your blood pressure drops so low or heart rate decreases or you lose about 5kg of weight, then the doctor will give you a synthetic form of the hormone vasopressin. If this hormone is able to bring back these parameters to normal then it means you have a central diabetes insipidus.
However, a diagnosis of nephrogenic diabetes insipidus will be made if you do not respond to vasopressin.
- Urine test
A routine urine analysis can also be conducted to identify the concentration of the various electrolytes and other substances in your urine.
How is diabetes insipidus treated?
The treatment is usually based on the type of diabetes insipidus you have. For central diabetes insipidus, since the problem has to do with absence of vasopressin, giving the synthetic analogues of this hormone is the treatment of choice.
The available medications are vasopressin and desmopressin. These may be taken as tablets, injections, nasal sprays or nasal drops.
For the nephrogenic diabetes insipidus, these agents won’t help much. In mild cases of nephrogenic diabetes insipidus, a well controlled diet may be prescribed to help alleviate some of the symptoms. These diets usually contain reduced amounts of salts, and proteins. If the condition is as a result of certain medications that you were taking, your doctor or pharmacist may ask you to stop taking them.
In some instances of nephrogenic diabetes insipidus, the use of thiazide diuretics and non-steroidal anti-inflammatory drugs (NSAIDs) have been used to help reduce the amount of urine produced by the kidneys.
Diabetes insipidus. (2016). Retrieved 17 July 2021, from https://www.mydr.com.au/diabetes/diabetes-insipidus/
Central Diabetes Insipidus – Hormonal and Metabolic Disorders – MSD Manual Consumer Version. (2021). Retrieved 17 July 2021, from https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/pituitary-gland-disorders/central-diabetes-insipidus?query=diabetes%20insipidus