diabetes insipidus

Diabetes Insipidus 

Definition

Diabetes insipidus (DI) is a disorder that causes the patient to produce tremendous quantities of urine. The massively increased urine output is usually accompanied by intense thirst.

Description

The balance of fluid within the body is maintained through a number of mechanisms. One important chemical involved in fluid balance is called antidiuretic hormone (ADH). ADH is produced by the pituitary, a small gland located at the base of the brain. In a healthy person and under normal conditions, ADH is continuously released. ADH influences the amount of fluid that the kidneys reabsorb into the circulatory system and the amount of fluid that the kidneys pass out of the body in the form of urine.

Production of ADH is regulated by the osmolality of the circulating blood. Osmolality refers to the concentration of dissolved chemicals (such as sodium, potassium, and chloride; together called solute) circulating in the fluid base of the blood (plasma). When there is very little fluid compared to the concentration of solute, the pituitary will increase ADH production. This tells the kidneys to retain more water and to decrease the amount of urine produced. As fluid is retained, the concentration of solute will normalize. At other times, when the fluid content of the blood is high in comparison to the concentration of solute, ADH production will decrease. The kidneys are then free to pass an increased amount of fluid out of the body in the urine. Again, this will allow the plasma osmolality to return to normal.

Diabetes insipidus occurs when either the amount of ADH produced by the pituitary is below normal (central DI), or the kidneys' ability to respond to ADH is defective (nephrogenic DI). In either case, a person with DI will pass extraordinarily large quantities of urine, sometimes reaching 10 or more liters each day. At the same time, the patient's blood will be very highly concentrated, with low fluid volume and high concentrations of solute.

DI occurs on average when a person is about 24 years old, and occurs more frequently in males than in females.

Causes and symptoms

DI may run in families. The cause of this type of DI is unknown. Other times, central DI can be caused by:

• an injury to the head
• brain surgery
• cancers that have spread to the pituitary gland (most commonly occurring with breast cancer)

• sarcoidosis (or other related disorders), causing destruction of the pituitary gland
• any condition or illness that causes decreased oxygen delivery to the brain
• the use of certain medications that decrease ADH production (like the antiseizure drug phenytoin)
• the excessive use of alcohol

Central DI may also occur in women who are pregnant or have just given birth, and in patients with AIDS who have suffered certain types of brain infections. Nephrogenic DI sometimes occurs in patients who are taking the medication lithium, patients who have high levels of blood calcium, and patients who are pregnant.

DI is easily confused with an entirely unrelated disorder, psychogenic polydipsia. Polydipsia refers to drinking large amounts of water. Psychogenic polydipsia is a psychiatric problem that makes a person drink huge quantities of water uncontrollably.

Symptoms of DI include extreme thirst and the production of tremendous quantities of urine. Patients with DI typically drink huge amounts of water, and usually report a specific craving for cold water. When the amount of water passed in the urine exceeds the patient's ability to drink ample replacement water, the patient may begin to suffer from symptoms of dehydration. These symptoms include weakness, fatigue, fever, low blood pressure, increased heart rate, dizziness, and confusion. If left untreated, the patient could lapse into unconsciousness and die.

Diagnosis

Diagnosis should be suspected in any patient with sudden increased thirst and urination. Laboratory examination of urine will reveal very dilute urine, made up mostly of water with no solute. Examination of the blood will reveal very concentrated blood, high in solute and low in fluid volume.

A water deprivation test may be performed. This test requires a patient to stop all fluid intake. The patient is weighed just before the test begins, and urine is collected and examined hourly. The test is stopped when:

• the patient has lost more than 5% of his or her original body weight
• the patient has reached certain limits of low blood pressure and increased heart rate
• the urine is no longer changing significantly from one sample to the next in terms of solute concentration.

The next step of the test involves injecting a synthetic form of ADH, with one last urine sample examined 60 minutes later. Comparing plasma and urine osmolality allows the doctor to diagnose either central DI, nephrogenic DI, partial DI, or psychogenic polydipsia.

Treatment

A number of medications can be given to decrease the quantity of fluid passed out into the urine. These include rasoprassin (Pitressin) injected and desmopressin acetate (DDAVP) inhaled through the nose. Other medications that may be given include some antidiuretic drugs (chlorpropamide, clofibrate, carbamazepine). Patients with nephrogenic DI, however, will also require special diets that restrict the amount of solute taken in. These patients are also treated with a type of medication called a thiazide diuretic.

Prognosis

Uncomplicated diabetes insipidus is controllable with adequate intake of water and most patients can lead normal lives.

Key terms

Concentration — Refers to the amount of solute present in a solution, compared to the total amount of solvent.

Dilute — A solution that has comparatively more fluid in it, relative to the quantity of solute.

Osmolality — A measure of the solute-to-solvent concentration of a solution.

Solute — Solid substances that are dissolved in liquid in order to make a solution.

Resources

Periodicals

Singer, Irwin, et al. "The Management of Diabetes Insipidus in Adults." Archives of Internal Medicine 157, no. 12 (June 23, 1997): 1293+.

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diabetes /di·a·be·tes/ (di″ah-be´tēz) any disorder characterized by excessive urine excretion. When used alone, the term refers to diabetes mellitus.

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adult-onset diabetes mellitus  type 2 d. mellitus.

brittle diabetes  type 1 diabetes mellitus characterized by wide, unpredictable fluctuations of blood glucose values and difficult to control.

bronze diabetes , bronzed diabetes hemochromatosis.

central diabetes insipidus  diabetes insipidus due to injury of the neurohypophyseal system, with a deficient quantity of antidiuretic hormone being released or produced, causing failure of renal tubular reabsorption of water.

gestational diabetes , gestational diabetes mellitus that with onset or first recognition during pregnancy.

growth-onset diabetes mellitus  type 1 d. mellitus.

diabetes insi´pidus  any of several types of polyuria in which the volume of urine exceeds 3 liters per day, causing dehydration and great thirst, as well as sometimes emaciation and great hunger.

insulin-dependent diabetes mellitus  (IDD) (IDDM) type 1 d. mellitus.

juvenile diabetes mellitus , juvenile-onset diabetes mellitus type 1 d. mellitus.

ketosis-prone diabetes mellitus  type 1 d. mellitus.

maturity-onset diabetes mellitus  type 2 d. mellitus.

diabetes mel´litus  (DM) a chronic syndrome of impaired carbohydrate, protein, and fat metabolism owing to insufficient secretion of insulin or to target tissue insulin resistance. It occurs in two major forms: type 1 d. mellitus and type 2 d. mellitus, which differ in etiology, pathology, genetics, age of onset, and treatment.

nephrogenic diabetes insipidus  inherited or acquired diabetes insipidus caused by failure of the renal tubules to reabsorb water in response to antidiuretic hormone, without disturbance in the renal filtration and solute excretion rates.

non–insulin-dependent diabetes mellitus  (NIDD) (NIDDM) type 2 d. mellitus.

preclinical diabetes  former name for impaired glucose tolerance.

renal diabetes  see under glycosuria.

subclinical diabetes  former name for impaired glucose tolerance.

Type I diabetes mellitus  type 1 d. mellitus.

type 1 diabetes mellitus  one of the two major types of diabetes mellitus, characterized by abrupt onset of symptoms (often in early adolescence), insulinopenia, and dependence on exogenous insulin; it is due to lack of insulin production by the pancreatic beta cells. With inadequate control, hyperglycemia, protein wasting, and ketone body production occur; the hyperglycemia leads to overflow glycosuria, osmotic diuresis, hyperosmolarity, dehydration, and diabetic ketoacidosis, which can progress to nausea and vomiting, stupor, and potentially fatal hyperosmolar coma. The associated angiopathy of blood vessels (particularly microangiopathy) affects the retinas, kidneys, and arteriolar basement membranes. Polyuria, polydipsia, polyphagia, weight loss, paresthesias, blurred vision, and irritability also occur.

Type II diabetes mellitus  type 2 d. mellitus.

type 2 diabetes mellitus  one of the two major types of diabetes mellitus, peaking in onset between 50 and 60 years of age, characterized by gradual onset with few symptoms of metabolic disturbance (glycosuria and its consequences) and control by diet, with or without oral hypoglycemics but without exogenous insulin required. Basal insulin secretion is maintained at normal or reduced levels, but insulin release in response to a glucose load is delayed or reduced. Defective glucose receptors on the pancreatic beta cells may be involved. It is often accompanied by disease of blood vessels, particularly the large ones, leading to premature atherosclerosis with myocardial infarction or stroke syndrome.

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diabetes in·sip·i·dus (n-sp-ds)

n.

A chronic metabolic disorder characterized by intense thirst and excessive urination, caused by a deficiency of the pituitary hormone vasopressin.

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diabetes insipidus

[insip′idəs]

a metabolic disorder caused by injury of the neurohypophyseal system. It is characterized by copious excretion of urine and excessive thirst, caused by deficient production or secretion of the antidiuretic hormone (ADH) or inability of the kidney tubules to respond to ADH. Rarely the symptoms are self-induced by an excessive water intake. The condition may be acquired, familial, idiopathic, neurogenic, nephrogenic, or psychogenic.

observations The onset may be dramatic and sudden, and urinary output may exceed 10 L in 24 hours. Diagnosis is established by a water deprivation test in which urine volume increases and urine osmolality decreases. A person with diabetes insipidus who is unconscious as result of trauma or surgery continues to produce massive quantities of urine. If fluids are not administered in adequate amounts, the patient becomes severely dehydrated and hypernatremic.

interventions In mild cases, no treatment is necessary. Vasopressin in an intramuscular injection or nasal spray is effective. Thiazide diuretics, by inducing a state of salt depletion, sometimes decrease the diuresis of water by as much as 50%.

nursing considerations Infants, small children, and the elderly are particularly vulnerable to serious circulatory disturbances when dehydrated. Therefore exceedingly careful monitoring is essential when the condition is suspected, especially after head surgery or trauma.

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diabetes (dībē´tēz),

n a deficiency condition involving carbohydrate metabolism and characterized by increased urination.

diabetes, bronzed,

n the combination of hemochromatosis and diabetes mellitus. The skin takes on a bronzed appearance as a result of the deposition of an iron-containing pigment in the skin.

diabetes, gestational

(jestāshnl),
n the term describing patients who acquire glucose intolerance when pregnant.

diabetes insipidus

(insip´ids),
n 1. a metabolic disturbance characterized by marked urinary excretion and great thirst but no elevation of sugar in the blood or urine.
n 2. a pituitary dysfunction characterized by an insufficient output of antidiuretic hormone, leading to polyuria and polydipsia.

diabetes, juvenile,

n an older term for diabetes mellitus occurring in children and adolescents, usually of a more severe and rampant nature than diabetes mellitus in adults, with consequent difficulty of regulation. Now considered a form of type 1 diabetes mellitus.

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diabetes insipidus

a metabolic disorder due to injury of the neurohypophyseal system, which results in a deficient quantity of antidiuretic hormone (ADH or vasopressin) being released or produced, resulting in failure of tubular reabsorption of water in the kidney. As a consequence, there is the passage of a large amount of urine having a low specific gravity, and great thirst. It may be acquired through infection, neoplasm or trauma to the posterior lobe of the pituitary gland or it may be inherited or idiopathic. Called also central diabetes insipidus.

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dipsogenic diabetes insipidus

see psychogenic diabetes insipidus (below).

nephrogenic diabetes insipidus

a rare form of diabetes insipidus, resulting from failure of the renal tubules to reabsorb water; there is excessive production of antidiuretic hormone but the tubules fail to respond to it.

psychogenic diabetes insipidus

a primary polydipsia resulting from a disorder of thirst control, or as a behavioral problem. The polyuria is secondary to the excessive water intake. Called also dipsogenic diabetes insipidus.

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diabetes insipidus

Endocrinology A condition characterized by defective water homeostasis due to a defect in ADH secretion, resulting in inadequate reabsorption of water by the kidney tubules and excretion of a large volume of dilute urine Types Central–due to a defect in the neurohypophysis (posterior pituitary) and/or hypothalamus; peripheral/nephrogenic–defect in the renal tubule