Diabetes insipidus is a condition where the body loses too much fluid through urination, causing a significant risk of dangerous dehydration as well as a range of other illnesses and conditions.
It is a rare disorder affecting the regulation of body fluid levels.
People with diabetes insipidus produce excessive amounts of urine, resulting in frequent urination and thirst. However, the underlying cause of these two symptoms differs from types 1 and 2 diabetes.
The disease takes two main forms: Mephrogenic diabetes insipidus and central or neurogenic diabetes insipidus.
Central diabetes insipidus occurs when the pituitary gland fails to secrete the hormone vasopressin, which regulates bodily fluids. In nephrogenic diabetes insipidus, vasopressin secretion is normal, but the kidneys do not correctly respond to the hormone.
Diabetes insipidus affects roughly 1 in every 25,000 people in the United States.
The main symptom of all cases of diabetes insipidus is frequently needing to pass high volumes of diluted urine.
The second most common symptom is polydipsia, or excessive thirst.
In this case, results from the loss of water through urine. The thirst prompts the person with diabetes insipidus to drink large volumes of water.
The need to urinate can disturb sleep. The volume of urine passed each day can be anywhere between 3 liters and 20 liters, and up to 30 liters in cases of central diabetes insipidus.
Another secondary symptom is dehydration due to the loss of water, especially in children who may not be able to communicate their thirst. Children may become listless and feverish, experience vomiting and diarrhea, and may show delayed growth.
Other people unable to help themselves to water, such as people with dementia, are also at risk of dehydration.
Extreme dehydration can lead to hypernatremia, a condition in which the sodium concentration of the serum in the blood becomes very high due to low water retention. The cells of the body also lose water.
Hypernatremia can lead to neurological symptoms, such as overactivity in the brain and nerve muscles, confusion, seizures, or even coma.
Without treatment, central diabetes inspidus can lead to permanent kidney damage. In nephrogenic DI, serious complications are rare, so long as water intake is sufficient.
Diabetes insipidus becomes a serious problem only for people who cannot replace the fluid that is lost in the urine. Access to water and other fluids makes the condition manageable.
If there is a treatable underlying cause of the high urine output, such as diabetes mellitus or drug use, addressing this should help resolve the diabetes insipidus.
For central and pregnancy-related diabetes insipidus, drug treatment can correct the fluid imbalance by replacing vasopressin. For nephrogenic diabetes insipidus, the kidneys will require treatment.
Vasopressin hormone replacement uses a synthetic analog of vasopressin called desmopressin.
The drug is available as a nasal spray, injection, or tablet, and is taken when needed.
Care should be taken not to overdose, as this can lead to excessive water retention and, in rare, severe cases, hyponatremia and fatal water intoxication.
The drug is otherwise generally safe when used at appropriate dosages, with few side effects. It is, however, not effective if diabetes insipidus occurs as a result of kidney dysfunction.
Mild cases of central diabetes insipidus may not need hormone replacement and can be managed through increased water intake.
Nephrogenic diabetes insipidus treatments may include:
- anti-inflammatory medicines, such as non-steroidal anti-inflammatory drugs (NSAIDS)
- diuretics, such as amiloride and hydrochlorothiazide
- reducing sodium intake and increasing water intake
A doctor may also advise a low-salt diet, and a person with diabetes insipidus may be referred to a nutritionist to organize a diet plan.
Reducing caffeine and protein intake and removing processed foods from the diet can be effective steps to controlling water retention, as well as consuming foods with high water content, such as melons.
Both types of diabetes insipidus are linked to a hormone called vasopressin but occur in different ways.
Vasopressin promotes water retention in the kidneys. This also keeps blood pressure at a healthy level.
The main symptom, excessive urine output, can have other causes. These would usually be ruled out before making a diagnosis of diabetes insipidus.
For example, undiagnosed or poorly managed diabetes mellitus can cause frequent urination.
Central diabetes insipidus
Central diabetes insipidus is caused by reduced or absent levels of vasopressin.
The condition can be present from birth, or primary. Secondary central diabetes insipidus is acquired later in life.
The cause of primary central diabetes insipidus is often unknown. Some causes result from an abnormality in the gene responsible for vasopressin secretion.
The secondary type is acquired through diseases and injuries that affect how vasopressin is produced.
These can include brain lesions resulting from head injuries, cancers, or brain surgery. Other body-wide conditions and infections can also trigger central diabetes insipidus.
Nephrogenic diabetes insipidus
Nephrogenic diabetes insipidus can also be inherited or acquired. This type affects the response of the kidneys to vasopressin.
Depending on a person’s genes, the condition results in the kidneys either completely or partially not responding to vasopressin. This affects water balance to varying degrees.
The acquired form of nephrogenic diabetes insipidus also reduces the kidneys’ ability to concentrate urine when water needs to be conserved.
Secondary nephrogenic diabetes insipidus can have numerous causes, including:
- kidney cysts that have developed due to a number of conditions, such as autosomal dominant polycystic kidney disease (ADPKD), nephronophthisis, medullary cystic disease complex, and medullary sponge kidney
- the release of an outlet tube obstruction from a kidney
- kidney infection
- high blood calcium levels
- some cancers
- certain medications, especially lithium, but also demeclocycline, amphotericin B, dexamethasone, dopamine, ifosfamide, ofloxacin, and orlistat
- rarer conditions, including amyloidosis, Sjögren’s syndrome, and Bardet-Biedl syndrome
- chronic hypokalemic nephropathy, a kidney disease caused by low blood potassium levels
- a cardiopulmonary bypass, which can affect vasopressin levels and may require treatment with desmopressin
Gestational diabetes insipidus
In rare cases, pregnancy can cause a disturbance of vasopressin, especially during the third trimester. This occurs due to the placenta releasing an enzyme that degrades vasopressin.
Pregnancy also causes a lower thirst threshold in women, stimulating them to drink more fluids, while other normal physiological changes during pregnancy can also affect the kidneys’ response to vasopressin.
Gestational diabetes insipidus is treatable during gestation and resolves 2 or 3 weeks following childbirth. The condition affects only a few women out of every 100,000 women who are pregnant.
Drugs that affect water balance
Diuretic drugs, commonly referred to as water pills, can also cause increased urine output.
Fluid imbalance can also occur after fluids are administered intravenously (IV). In these cases, the rate of the drip is stopped or slowed, and the need to urinate resolves. High-protein tube feeds may also increase urine output.
The water deprivation test is a reliable test to help diagnose diabetes insipidus. However, the test has to be performed by a specialist, as it can be dangerous without proper supervision.
The water deprivation test involves allowing a patient to become increasingly dehydrated while taking blood and urine samples.
Vasopressin is also given to test the kidneys’ ability to conserve water during dehydration.
In addition to managing the dangers of dehydration, close supervision also allows psychogenic polydipsia to be definitively ruled out. This condition causes a person to compulsively or habitually drink large volumes of water.
Someone with psychogenic polydipsia may try to drink some water during this test, despite strict instructions against drinking.
Samples taken during the water deprivation test are assessed to determine the concentration of urine and blood, and to measure levels of electrolytes, particularly sodium, in the blood.
Under normal circumstances, dehydration triggers the secretion of vasopressin from the pituitary gland in the brain, telling the kidneys to conserve water and concentrate the urine.
In diabetes insipidus, either insufficient vasopressin is released, or the kidneys are resistant to the hormone. Testing these dysfunctions will help define and treat the type of diabetes insipidus.
The two types of the condition are further defined if the urine concentration then responds to injection or nasal spray of vasopressin.
Improvements in urine concentration demonstrate that the kidneys are responding to the hormone’s message to improve water conservation, suggesting that the diabetes insipidus is central.
If the kidneys do not respond to the synthetic vasopressin, the cause is likely to be nephrogenic.
Before the water deprivation test is carried out by specialists, investigations are done to rule out other explanations for the high volumes of diluted urine, including:
- Diabetes mellitus: Blood sugar levels in types 1 and 2 diabetes affect urine output and thirst.
- Current courses of medication: The doctor will rule out the role of any current medications, such as diuretics, in affecting water balance.
- Psychogenic polydipsia: Excessive water intake as a result of this condition can create the high urine output. It can be associated with psychiatric illnesses, such as schizophrenia.
Diabetes insipidus and diabetes mellitus are not related to one another. Their symptoms, however, can be similar.
The words ‘mellitus’ and ‘insipidus’ come from the early days of diagnosing the condition. Doctors would taste the urine to gauge sugar content. If the urine tasted sweet, it meant that too much sugar was leaving the body in the urine, and the doctor would reach a diabetes mellitus diagnosis.
However, if the urine tasted bland or neutral, it meant that water concentration was too high, and diabetes inspidus would be diagnosed. “Insipidus” comes from the word “insipid,” meaning weak or tasteless.
In diabetes mellitus, elevated blood sugar prompts the production of large volumes of urine to help remove the excess sugar from the body. In diabetes insipidus, it is the water balance system that is not functioning correctly.
Diabetes mellitus is far more common than diabetes insipidus. Diabetes insipidus, however, progresses far more rapidly.
Of the two conditions, diabetes mellitus is more harmful and harder to manage.
Diabetes inspidus is often difficult or impossible to prevent, as it results either from genetic problems or other conditions. However, symptoms can be managed effectively.
It is often a lifelong condition. With ongoing treatment, the outlook can be good.