What is diabetes insipidus?
In order to regulate thirst and the supply of water to the body, the pituitary gland secretes in its posterior part, the so-called neurohypophysis, a hormone, antidiuretic hormone (ADH), also called vasopressin (AVP), which is responsible for enhancing the reabsorption of water at the renal level and thereby regulate plasma osmolarity, as well as the volume of plasma fluid and consequently the pressure and concentration of various substances in the blood.
If for some reason ADH cannot exert its function, the kidney does not recover as much water as it should, with the consequent repercussions on the organism. If this situation occurs, it will be said that the patient suffers from an impairment due to the lack of functioning of the ADH, which is known as diabetes insipidus.
This affectation receives this name not because it has something to do from a causal point of view with diabetes due to lack of insulin (diabetes mellitus), but by analogy with the symptoms of increased thirst, water intake and diuresis that occur. they give in both pathologies. The absence of glucose loss in urine means that this entity caused by the alteration of ADH receives the qualification of insipid, to differentiate it from diabetes mellitus (sweet).
How is it produced?
The absence of antidiuretic hormone (ADH) can be divided into two large groups depending on the cause that originates it:
- Central diabetes insipidus, due to alteration in the production of ADH at the pituitary level.
- Renal diabetes insipidus, due to impaired kidney response to ADH.
Central diabetes insipidus may be due to an absence of ADH production at the level of the neurohypophysis, totally or partially, or it may be due to an alteration of the receptors that detect plasma osmolarity levels and that when faced with an increase in They activate the production of ADH, either because the release threshold is higher than normal, or because they do not respond to increases in osmolarity no matter how much it increases.
Central diabetes insipidus
It is of unknown origin in 25% -30% of cases and usually appears in adults. In 20% -25% of cases it is due to head trauma, in 15% -20% to pituitary tumors and to a lesser extent to other entities such as sarcoidosis, histiocytosis, infections, vascular disorders, alcohol or other substances. There is an autosomal dominant familial form that appears in children and a syndrome of autosomal recessive inheritance, the so-called Wolfram syndrome or DIDMOAD syndrome that associates diabetes insipidus, diabetes mellitus, ocular atrophy and deafness.
Kidney diabetes insipidus
It is due to an alteration in the control of osmolarity at the renal level due to alteration of ADH receptors. The main causes that can cause renal diabetes insipidus are hypercalcemia, hypokalemia, and certain interstitial tubular diseases. There is a familiar form of appearance in children of inheritance linked to the X chromosome in a recessive form, which can lead to serious dehydration problems, as well as another less frequent autosomal recessive form.
Symptoms
The lack of ADH causes plasma osmolarity to increase and not enough fluid is retained at the renal level, resulting in persistent polyuria. This triggers a feeling of severe thirst, so the patient constantly drinks water, which is known as polydipsia. Despite this, he cannot quench his thirst, so he continues to drink up to a total of 4-6 liters of water a day, which in extreme cases can reach 16 liters a day.
The onset of symptoms is usually abrupt and is accompanied by poorly concentrated urine and low osmolarity, unlike in blood, which will be high.
Diagnosis
The diagnosis should be suspected in any person with compatible symptoms, with a recent increase and sudden onset of a sensation of insatiable thirst associated with an increase in water intake and diuresis. The family history of diabetes insipidus should be investigated, as well as the existence of possible causes such as head trauma, tumors, infections or other pathologies.
The essential diagnosis will be based on the determination of the osmolarity in urine, which will be decreased, below 300 mosM / kg, with a urinary density also decreased (below 1010), as well as a high plasma osmolarity, above 295 mosM / kg.
To differentiate whether the cause is central or renal, a dose of ADH will be administered to the patient if he already has plasma osmolarity levels> 295 mosM / kg (if not, he will first be left without drinking for about 8 hours to achieve those levels). If after ADH administration the plasma osmolarity drops and the urinary osmolarity rises significantly, the cause will be the absence of ADH, that is, it will be central, while if the levels do not change despite the presence of ADH, the cause will be renal.
ADH levels in the blood could be determined, but it is not usually done due to the high cost of its determination.
Performing a brain nuclear magnetic resonance will show the neurohypophysis less bright than is usual in a normal person, although this imaging test is not necessary for diagnosis.
Treatment
Treatment will be different depending on the central or renal origin of diabetes insipidus.
- In diabetes insipidus of central origin, due to a lack of ADH, the patient will be administered the missing hormone, in the form of ADH or desmopressin. In those patients with a certain level of ADH production, it has been seen that the administration of chlorpropamide or carbamazepine can stimulate their secretion.
- In the case of diabetes insipidus of renal origin, treatment will be aimed at restricting the intake of salt and fluid and the use of diuretics such as thiazides. Sodium levels in the blood should be controlled to avoid states of dehydration or hyponatremia.
Precautionary measures
Since most of the time the cause is of unknown origin, there are no preventive measures against this disease. However, people with these symptoms should be instructed to go to the endocrinologist as soon as possible.
(Updated at Apr 14 / 2024)