Diabetes insipidus
Introduction
Diabetes means "to pass through". Diabetes insipidus reflects that the kidney is unable to concentrate urine and it is secreted as hypotonic compared to plasma, cue to antidiuretic hormone (ADH) not working as it should by incorporating water channels to the luminal side of the collecting ducts. The collecting ducts are therefore impermeable to water. It is possible to lose large amounts of water through urine, over 20 litres per day.
Causes
We distinguish between nephrogenic and neurogenic diabetes insipidus. In neurogenic diabetes insipidus, there is a lack of ADH due to disease/damage to the pituitary/hypothalamus. In nephrogenic diabetes insipidus, ADH is produced as normal, but the hormone does not work as it should due to disease/damage to the tubular cells.
Table of the most common causes of diabetes insipidus
| Causes |
Examples |
| Renal diabetes insipidus | Drugs |
| Lithium, demeclocycline, amphotericin B ++ |
| Hypercalcemia |
| Hypokalemia |
| Obstructive nephropathy |
| Congenital gene mutations |
| Neurogenic diabetes insipidus | Pituitary operations |
| Head trauma |
| Pituitary tumors |
| Vascular catastrophes |
| Infections |
| Sarcoidosis |
| Autoimmune |
| Congenital gene mutations |
Clinical presentation
Diabetes insipidus presents with polyuria and thirst and it can present in a complete or partial form. The fluid loss can be quite large in the complete abscence of ADH, and if patients cannot replace the loss, then the dehydration will quickly become severe. Hypernatremia and hypokalemia occur due to activation of aldosterone from activation of the renin-angtiotensin system (RAS). In relative ADH deficiency or renal diabetes insipidus with slightly reduced ADH response, the diagnosis can be difficult to detect. The diagnosis is confirmed by measuring low urine osmolality despite elevated plasma osmolality after a period of thirst.
Prognosis and treatment
In the complete form, the disorder is life-threatening due to the danger of dehydration and electrolyte imbalances. Examination for underlying causes is necessary. Neurogenic diabetes insipidus can be treated with ADH in the form of nasal spray or through iv.
In nephrogenic diabetes insipidus, external administration of the hormone will have no effect. The triggering cause must be removed. Low sodium and low protein diet will lead to reduced diuresis in patients with nephrogenic diabetes insipidus.
Some diuretics can paradoxically work positively on diabetes insipidus. Thiazide diuretics, combined with a low sodium diet, results in mild hypovolemia that increases proximal reabsorption and reduces the volume of urine at the ADH sensitive areas distally in the nephron, thereby limiting polyuria.
Amiloride treatment can be beneficial in combination with thiazides by working synergistically through the same mechanism. In addition, amiloride will be especially beneficial in lithium-induced diabetes insipidus, as the drug blocks Na channels luminally in the collecting duct. Lithium enters cells through these channels and affects ADH response, Amiloride, therefore, counteracts this effect of lithium. Loop diuretics are unsuitable in limiting polyuria.
Read more about diabetes insipidus