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Adipsia

Adipsia, also known as hypodipsia, is a symptom of inappropriately decreased or absent feelings of thirst. It involves an increased osmolality or concentration of solute in the urine, which stimulates secretion of antidiuretic hormone from the hypothalamus to the kidneys. This causes the person to retain water and ultimately become unable to feel thirst. Due to its rarity, the disorder has not been the subject of many research studies. Adipsia may be seen in conditions such as diabetes insipidus and may result in hypernatremia. It can occur as the result of abnormalities in the hypothalamus, pituitary and corpus callosum, as well as following pituitary/hypothalamic surgery. It is possible for hypothalamic dysfunction, which may result in adipsia, to be present without physical lesions in the hypothalamus, although there are only four reported cases of this. There are also some cases of patients experiencing adipsia due to a psychiatric disease. In these rare psychogenic cases, the patients have normal levels of urine osmolality as well as typical ADH activity.

                                               

Diabetes insipidus

Diabetes insipidus is a condition characterized by large amounts of dilute urine and increased thirst. The amount of urine produced can be nearly 20 liters per day. Reduction of fluid has little effect on the concentration of the urine. Complications may include dehydration or seizures. There are four types of DI, each with a different set of causes. Central CDI is due to a lack of the hormone vasopressin antidiuretic hormone. This can be due to injury to the hypothalamus or pituitary gland or genetics. Nephrogenic NDI occurs when the kidneys do not respond properly to vasopressin. Dipsogenic DI is a result of excessive fluid intake due to damage to the hypothalamic thirst mechanism. It occurs more often in those with certain psychiatric disorders or on certain medications. Gestational DI occurs only during pregnancy. Diagnosis is often based on urine tests, blood tests and the fluid deprivation test. Diabetes mellitus is a separate condition with an unrelated mechanism, though both can result in the production of large amounts of urine. Treatment involves drinking sufficient fluids to prevent dehydration. Other treatments depend on the type. In central and gestational DI, treatment is with desmopressin. Nephrogenic DI may be treated by addressing the underlying cause or the use of a thiazide, aspirin or ibuprofen. The number of new cases of diabetes insipidus each year is 3 in 100.000. Central DI usually starts between the ages of 10 and 20 and occurs in males and females equally. Nephrogenic DI can begin at any age. The term "diabetes" is derived from the Greek word meaning siphon.

                                               

Fluid deprivation test

A fluid or water deprivation test is a medical test which can be used to determine whether the patient has diabetes insipidus as opposed to other causes of polydipsia. The patient is required, for a prolonged period, to forgo intake of water completely, to determine the cause of the thirst. This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH a synonym for vasopressin during this test is also necessary. If there is no change in the water loss despite fluid deprivation, desmopressin may be administered to distinguish between the two types of diabetes insipidus which are central & nephrogenic diabetes insipidus. The time of deprivation may vary from 4 to 18 hours. The serum osmolality and urine osmolality are both measured in the test.

                                               

Polydipsia

Polydipsia is excessive thirst or excess drinking. The word derives from the Greek πολυδίψιος "very thirsty", which is derived from πολύς + δίψα. Polydipsia is a nonspecific symptom in various medical disorders. It also occurs as an abnormal behaviour in some non-human animals, such as in birds.

                                               

Primary polydipsia

Primary polydipsia, or psychogenic polydipsia, is a form of polydipsia characterised by excessive fluid intake in the absence of physiological stimuli to drink. Psychogenic polydipsia which is caused by psychiatric disorders, often schizophrenia, is often accompanied by the sensation of dry mouth. Some forms of polydipsia are explicitly non-psychogenic. Primary polydipsia is a diagnosis of exclusion.

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