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Diabetes insipidus

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For the disease most commonly associated with the generic term "diabetes", see Diabetes mellitus.
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Diabetes insipidus
ICD-10 E232 N251
ICD-9 253.5 588.1
OMIM 304800 125800
DiseasesDB 3639
MedlinePlus 000377
CentralTemplate:MedlinePlus2
CongenitalTemplate:MedlinePlus2
Nephrogenic Template:MedlinePlus2
eMedicine med/543 ped/580
MeSH {{{MeshNumber}}}

Diabetes insipidus (DI) (Greek διαβαίνειν diabainein - to pass through and Latin insipidus - without taste) is a condition characterized by excretion of large amounts of severely diluted urine, which cannot be reduced when fluid intake is reduced. It denotes inability of the kidney to concentrate urine. DI is caused by a deficiency of antidiuretic hormone (ADH), also known as vasopressin, due to the destruction of the back or "posterior" part of the pituitary gland where vasopressin is normally released from, or by an insensitivity of the kidneys to that hormone. It can also be induced iatrogenically by various drugs.

Signs and symptomsEdit

Excessive urination and extreme thirst (especially for cold water and sometimes ice or ice water) are typical for DI. Symptoms of diabetes insipidus are quite similar to those of untreated diabetes mellitus, with the distinction that the urine is not sweet as it does not contain glucose and there is no hyperglycemia (elevated blood glucose). Blurred vision is a rarity. Signs of dehydration may also appear in some individuals since the body cannot conserve much (if any) of the water it takes in.

The extreme urination continues throughout the day and the night. In children, DI can interfere with appetite, eating, weight gain, and growth as well. They may present with fever, vomiting, or diarrhea. Adults with untreated DI may remain healthy for decades as long as enough water is drunk to offset the urinary losses. However, there is a continuous risk of dehydration.

DiagnosisEdit

In order to distinguish DI from other causes of excess urination, blood glucose levels, bicarbonate levels, and calcium levels need to be tested. Measurement of blood electrolytes can reveal a high sodium level (hypernatremia as dehydration develops). Urinalysis demonstrates a dilute urine with a low specific gravity. Urine osmolarity and electrolyte levels are typically low.

A fluid deprivation test helps determine whether DI is caused by:

  1. excessive intake of fluid
  2. a defect in ADH production
  3. a defect in the kidneys' response to ADH

This test measures changes in body weight, urine output, and urine composition when fluids are withheld and as dehydration occurs. The body's normal response to dehydration is to concentrate urine and conserve water, so urine becomes more concentrated and urination becomes less frequent. Those with DI continue to urinate large amounts of dilute urine in spite of not drinking any fluids. Sometimes measuring blood levels of ADH during this test is also necessary.

To distinguish between the main forms, desmopressin stimulation is also used; desmopressin can be taken by injection, a nasal spray, or a tablet. While taking desmopressin, a patient should drink fluids or water only when thirsty and not at other times, as this can lead to sudden fluid accumulation in central nervous system. If desmopressin reduces urine output and increases osmolarity, the pituitary production of ADH is deficient, and the kidney responds normally. If the DI is due to renal pathology, desmopressin does not change either urine output or osmolarity.

If central DI is suspected, testing of other hormones of the pituitary, as well as magnetic resonance imaging (MRI), is necessary to discover if a disease process (such as a prolactinoma, or histiocytosis, syphilis, tuberculosis or other tumor or granuloma) is affecting pituitary function. Thankfully most people with this form either have experienced past head trauma or simply have stopped ADH production for no apparent reason.

Habit drinking (in its severest form termed psychogenic polydipsia) is the most common imitator of diabetes insipidus at all ages. While many adult cases in the medical literature are associated with mental disorders, most patients with habit polydipsia have no other detectable disease. The distinction is made during the water deprivation test, as some degree of urinary concentration above isosmolar is usually obtained before the patient becomes dehydrated.

PathophysiologyEdit

Electrolyte and volume homeostasis is a complex mechanism that balances the body's requirements for blood pressure and the main electrolytes sodium and potassium. In general, electrolyte regulation precedes volume regulation. When the volume is severely depleted, however, the body will retain water at the expense of deranging electrolyte levels.

The regulation of urine production occurs in the hypothalamus, which produces antidiuretic hormone (ADH or vasopressin) in the supraoptic and paraventricular nuclei. After synthesis, the hormone is transported in neurosecretory granules down the axon of the hypothalamic neuron to the posterior lobe of the pituitary gland where it is stored for later release. In addition, the hypothalamus regulates the sensation of thirst in the ventromedial nucleus by sensing increases in serum osmolarity and relaying this information to the cortex.

The main effector organ for fluid homeostasis is the kidney. ADH acts by increasing water permeability in the collecting ducts and distal convoluted tubule, specifically it acts on proteins called aquaporins which open to allow water into the collecting duct cells. This increase in permeability allows for reabsorption of water into the bloodstream, thus concentrating the urine.

ClassificationEdit

There are several forms of DI:

Cranial diabetes insipidusEdit

Cranial diabetes insipidus (sometimes central or neurogenic DI) is due to damage to the hypothalamus or pituitary due to a tumor, trauma (such as a fracture to the base of the skull), stroke,[1] neurosurgery or some rather rare causes (which include hemochromatosis, sarcoidosis, histiocytosis, diseases that can form masses in the vicinity like a tuberculoma or syphilis and some genetic disorders). If the hypothalamus is damaged, the feeling of thirst may be completely absent.

NephrogenicEdit

Nephrogenic diabetes insipidus is due to the inability of the kidney to respond normally to ADH.

  • There are hereditary causes. Inherited forms have been associated with AVPR2 (X-linked)[2] and AQP2 (autosomal).[3]. Approximately 90% are due to mutations of the ADH V2 receptor, and 10% mutations of the aquaporin 2 water channel), but these are rare (incidence is around 4 per million live births). Most are male, because V2 receptor mutations are x-linked recessive defects.

DipsogenicEdit

Dipsogenic DI is due to a defect or damage to the thirst mechanism, which is located in the hypothalamus[7]. This defect results in an abnormal increase in thirst and fluid intake that suppresses ADH secretion and increases urine output. Desmopressin is ineffective, and can lead to fluid overload as the thirst remains.

GestationalEdit

Gestational DI only occurs during pregnancy. While all pregnant women produce vasopressinase in the placenta, which breaks down ADH, this can assume extreme forms in GDI. [8]

Most cases of gestational DI can be treated with desmopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational DI, and desmopressin should not be used.

TreatmentEdit

Central DI and gestational DI respond to desmopressin. Carbamazepine, an anti-convulsive medication, has also had some success in this type of DI. Also gestational DI tends to abate on its own 4 to 6 weeks following labour, though some women may develop it again in subsequent pregnancies. In dipsogenic DI, desmopressin is not usually an option.

Desmopressin will be ineffective in nephrogenic DI. Instead, the diuretic hydrochlorothiazide (HCT or HCTZ) or indomethacin can improve nephrogenic diabetes insipidus; HCT is sometimes combined with amiloride to prevent hypokalemia. Again, adequate hydration is important for patients with DI, as they may become dehydrated easily.

SourcesEdit

  1. Sweeney AT, Blake MA, Adelman LS, et al (2004). Pituitary apoplexy precipitating diabetes insipidus. Endocr Pract 10 (2): 135–8.
  2. OMIM 304800
  3. OMIM 125800
  4. Christensen S, Kusano E, Yusufi AN, Murayama N, Dousa TP (June 1985). Pathogenesis of nephrogenic diabetes insipidus due to chronic administration of lithium in rats. J. Clin. Invest. 75 (6): 1869–79.
  5. Marples D, Frøkiaer J, Dørup J, Knepper MA, Nielsen S (April 1996). Hypokalemia-induced downregulation of aquaporin-2 water channel expression in rat kidney medulla and cortex. J. Clin. Invest. 97 (8): 1960–8.
  6. 6.0 6.1 Carney S, Rayson B, Morgan T (October 1976). A study in vitro of the concentrating defect associated with hypokalaemia and hypercalcaemia. Pflugers Arch. 366 (1): 11–7.
  7. Perkins RM, Yuan CM, Welch PG (March 2006). Dipsogenic diabetes insipidus: report of a novel treatment strategy and literature review. Clin. Exp. Nephrol. 10 (1): 63–7.
  8. Kalelioglu I, Kubat Uzum A, Yildirim A, Ozkan T, Gungor F, Has R (2007). Transient gestational diabetes insipidus diagnosed in successive pregnancies: review of pathophysiology, diagnosis, treatment, and management of delivery. Pituitary 10 (1): 87–93.
  • The public domain document "Diabetes Insipidus", NIH Publication No. 01-4620, December 2000.

External linksEdit




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