Diabetes Insipidus

Diabetes Insipidus

Also called: Water Diabetes, DI

Summary

Diabetes insipidus (DI) is a rare disorder in which the kidneys stop conserving water. Despite the similarities in name and some symptoms, it should not be confused with diabetes mellitus because these two endocrine conditions are unrelated.

In its most common form, DI is caused by damage to a part of the brain called the hypothalamus, usually due to tumors or surgery near this region. Diabetes mellitus, on the other hand, is caused by a lack of or difficulty using insulin, a hormone needed to process glucose (blood sugar) for energy.

The two most common signs of DI are increased thirst and increased urination, which are also common signs of diabetes mellitus. However, DI arises when there is a decrease in the level of a specific hormone that is responsible for instructing the kidneys to conserve water and help concentrate the urine.

Other symptoms of DI include dehydration and urine that is more clear and watery than normal. Depending on the cause, DI can be a temporary or permanent condition. Treatments may include medication, such as hormone therapy or diuretics.

About diabetes insipidus

Diabetes insipidus (DI) is a rare endocrine disorder in which the kidneys are no longer able to conserve water or concentrate the urine. This, in turn, leads to excessive thirst (polydipsia), an increased intake of fluids and thus excessive urination (polyuria).

Despite the similar names and certain symptoms in common, including increased thirst and increased urination, diabetes mellitus and diabetes insipidus are not related diseases. In the case of DI, sometimes called “water diabetes,” the body is in an abnormal state of water diuresis (overproduction of diluted urine). With diabetes mellitus, sometimes called “sugar diabetes,” the body is in an abnormal state of osmotic diuresis (excess urine caused by high glucose).

A part of the brain called the hypothalamus is responsible for producing the antidiuretic hormone ADH, which is commonly referred to as vasopressin. This hormone signals the kidneys to conserve water by creating concentrated urine. If there is a lack of vasopressin, the kidneys will no longer absorb excess water, leading to diabetes insipidus. This causes the body to rapidly lose water in the form of dilute urine. This form of DI, commonly referred to as central diabetes insipidus, is often a result of damage to the hypothalamus or pituitary gland caused by surgery, infection, tumor or a head injury.

DI can also be caused by certain medications, such as lithium, and it can be inherited. About 25 percent of the time, a definitive cause cannot be found, according to the American Academy of Physicians. The prevalence of all types of DI is rare, occurring in 1 out of 25,000 people.

Central DI (also called neurogenic DI) can be either a temporary or permanent disorder, depending on the injury or underlying condition. Although all forms of DI are rare, central DI is the most common form of diabetes insipidus.

Types and differences of diabetes insipidus

Diabetes insipidus (DI) is an uncommon disease that develops when the kidneys are no longer able to conserve water or concentrate the urine. There are four types of DI:

  • Neurogenic or central DI. This form of the disease is by far the most common. It develops from a lack of antidiuretic hormone (ADH), more commonly referred to as vasopressin. Central DI is most commonly caused by brain tumors, head trauma, granulomatous (tumor-like) diseases or an autoimmune reaction, or is sometimes inherited from a parent.
  • Nephrogenic DI. This form of diabetes insipidus comes from kidney defects that make the organ unable to respond to ADH. DI can develop because of hypokalemia (low potassium in the blood), hypercalcemia (excess calcium in the blood), or certain medications, such as lithium (used to treat bipolar disorders). Nephrogenic DI may be caused by various kidney disorders, such as polycystic kidney disease. It can also be inherited.

For those who have the inherited form of diabetes insipidus, symptoms can start within weeks of birth. However, they often go undetected or their significance can be missed for months and possibly even years. Early symptoms include fever, irritability, constipation, failure to thrive, lack of appetite, vomiting and high levels of sodium in the blood.

  • Primary polydipsic DI. Also known as primary polydipsia or dipsogenic DI, caused by excessive fluid intake, which suppresses ADH. Frequently, polydipsic DI is seen in people with abnormally high thirst (polydipsia) as a result of psychological or emotional disturbances. These conditions can sometimes be referred to as psychogenic DI, whereas high fluid intake from fad diets is referred to as iatrogenic DI. The term “iatrogenic” generally refers to a condition caused by treatment.
  • Gestagenic DI. This extremely rare form of the disease appears only during pregnancy. Gestagenic DI develops on the rare occasion that the placenta retards the production of vasopressin. It usually disappears after pregnancy, but may reoccur with subsequent pregnancies.

In about a quarter of cases, a definitive cause cannot be found for diabetes insipidus. Physicians sometimes use the term idiopathic to describe conditions whose cause is unknown.

Signs and symptoms of diabetes insipidus

The most notable symptom of diabetes insipidus (DI) is a feeling of thirst that causes a person to drink large volumes of water to compensate for water being lost in the urine. This excessive thirst (polydipsia) in turn leads to drinking a lot of fluids, causing an excessive amount of urine (polyuria) that is clear and watery.

According to the Diabetes Insipidus Foundation, excessive thirst in an adult can be defined as drinking more than four quarts (3.8 liters) a day. Excessive urination can be defined as more than 50 milliliters per gram of body weight, about 3.5 quarts daily for a 150-pound (68-kilogram) adult.

Other signs and symptoms of diabetes insipidus may include:

  • Dry skin
  • Dry mucous membranes
  • Constipation
  • Muscle weakness or lethargy
  • Dehydration, possibly leading to dizziness and general weakness, a sunken appearance to eyes, fever, rapid heart rate or weight loss
  • Bedwetting
  • The need to urinate during the night – sometimes getting up two to three times each night (in middle-age and elderly men, enlargement of the prostate gland is a common cause of this symptom)
  • Fatigue from getting up during the night to urinate

Diagnosis methods for diabetes insipidus

Because the most common cause of polyuria and polydipsia is diabetes mellitus (DM), diabetes insipidus (DI) may be overlooked by physicians. An incorrect diagnosis of DM instead of DI can not only cause needless suffering, but it can also lead to severe dehydration and, in rare cases, brain damage or possibly death. A proper diagnosis is also important when considering that DI may be an early sign of another serious underlying condition, such as a brain tumor.

To make a diagnosis of diabetes insipidus, a physician may take a medical history that includes:

  • A review of conditions or illnesses that could be causing or contributing to dehydration
  • A review of medications that the patient is taking
  • A review of recent drinking, urinary and bowel habits

A physical examination should include taking vital signs including pulse, blood pressure and an evaluation of any difficulty swallowing. When more water than salt is being lost, the physician may attempt to rule out excessive diuretic use, infections and fever based on the medical history and physical examination.

A diagnosis of DI is also based on blood tests and urine tests. If DI is suspected, most physicians will recommend a water deprivation test. Because of the various reasons for developing DI, an ultrasound or MRI (magnetic resonance imaging) may be used to check for brain injury, tumors or any signs of kidney disease.

Some of the more common diagnostic tests used to screen for diabetes insipidus include:

  • Measurements of antidiuretic hormone (ADH, also called vasopressin) and other substances in blood and urine before and during a water deprivation or dehydration test.
  • MRI of the brain.
  • A closely monitored administration of a synthetic antidiuretic hormone known as DDAVP.
  • The water deprivation test. During this test the patient is not permitted to drink any water. The weight of the patient will be checked and urine and blood tests performed. Urine volume and the ability of the kidneys to concentrate urine is checked every hour. Blood concentration is measured every two hours.

However, if the DI appeared in infancy or early childhood or if it affects other members of the patient’s family, a genetic test may be ordered to determine if it is an inherited form of DI.

Treatment options for diabetes insipidus

Treatment options for diabetes insipidus (DI) vary greatly depending on the underlying cause of this rare condition. If possible, the cause of the underlying condition should be treated. Central DI may be controlled with medication, which normally includes some form of hormone replacement therapy. The hormone therapy includes administering vasopressin, usually as a nasal spray, tablets or injections under the skin.

However, vasopressin is not effective for patients with nephrogenic or primary polydipsic DI. Thiazide diuretics, anti-inflammatory medications or a sodium-restricted diet are often used for those who have nephrogenic DI. In addition, patients with nephrogenic DI caused by medications such as lithium often see a return of normal kidney function once the medication is stopped.

If the nephrogenic DI is the extremely rare hereditary form, increased fluid intake that matches the urine output and possibly the addition of medications that lower urine output may be all that is needed for treatment. Primary polydipsic DI is treated by limiting the patient’s fluid intake.

Depending on the underlying disorder or condition that led to DI, when properly diagnosed and treated, diabetes insipidus does not cause severe problems or reduce life expectancy.

Because complications from dehydration can lead to confusion and impaired mental function, patients with DI are urged to wear a medical alert bracelet or necklace so as to alert bystanders and healthcare workers in an emergency.

Prevention methods for diabetes insipidus

In most cases, it is not possible to prevent diabetes insipidus. In the case of an injury-caused development of the disease, people can take precautions to reduce their risk of head injury by following sports safety guidelines for children, adolescents and adults. In addition, the prompt treatment of infections may reduce the risk of developing diabetes insipidus.

Questions for your doctor on diabetes insipidus

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about diabetes insipidus (DI):

  1. Could my increased thirst and increased urination be due to diabetes insipidus?
  2. What else could be causing my symptoms?
  3. What tests for DI might I undergo, and what do they involve?
  4. What do my test results show? Which type of DI do I have?
  5. What caused my DI?
  6. Am I at risk of dehydration or other complications?
  7. What are my treatment options, and which do you recommend?
  8. How can DI affect my diabetes mellitus?
  9. How can diabetes mellitus affect my DI?
  10. Should my family members be checked for DI?
  11. Is there any way I can prevent DI?
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