Hypodipsia
| Adipsia | |
|---|---|
| Synonyms | hypodipsia |
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| Molecular structure of vasopressin. This hormone is related to Type A and Type B adipsia. | |
| Classification and external resources | |
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 (ADH) 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.
Type A (essential hypernatremia syndrome) involves an increase of the level in which solvent molecules can pass through cell membranes (osmotic threshold) for vasopressin release and the activation of the feeling of thirst. This is the most characterized sub-type of adipsia, however there is no known cause for Type A adipsia. There is debate over whether osmoreceptor resetting could lead to the increase in threshold. Other studies have shown that it is the loss of osmoreceptors, not resetting, that cause the change in threshold. Patients with Type A adipsia can be at risk of seizures if they rapidly re-hydrate or quickly add a significant amount of sodium into their bodies. If not treated, Type A adipsia could result in both a decrease in the size of the brain and bleeding in the brain.
Type B adipsia occurs when vasopressin responses are at decreased levels in the presence of osmotic stimuli. Although minimal, there is still some secretion of AVP. This type may be due to some elimination of osmoreceptors.
Type C adipsia (type C osmoreceptor dysfunction) involves complete elimination of osmoreceptors, and as a result have no vasopressin release when there normally would be. Type C is generally the adipsia type found in patients with adipsic diabetes insipidus.
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