Diabetes Insipidus

What is diabetes insipidus?

Diabetes insipidus is caused by the lack of secretion of antidiuretic hormone (ADH) by the hypothalamus. This is the most frequent case. In nephrogenic diabetes insipidus, the secreted hormone does not act on the kidney tubules, which become resistant to its action. Normally, the kidneys filter a large amount of water through the glomeruli and then reabsorb it in the tubule, after which it returns into the bloodstream. A fraction of the renal cavities are retained and together with waste, they form the urine. The lack of antidiuretic hormone ADH leads to the inability of the renal tubule to reabsorb the filtered water through the glomeruli.

 

The signs of the disease

Clinically, the disease manifests itself progressively or suddenly by polyuria (increased urination) and cannot be cured. The urine volume is increased and may reach 8 to 10 liters per day and sometimes even 15 to 20 liters. The urine is pale as water and contains neither sugar nor albumin. This polyuria is accompanied by polydipsia, i.e. the patient is always thirsty and insatiable. They drink day and night and can never quench their thirst.

Otherwise, they are in a fairly good condition unless they are hyper-hydrated (headaches, nausea) or dehydrated (they cannot drink as much as they need to).

 

Clinical examination is normal.

Additional examinations (blood and urinary ionograms) are normal, except for rare cases of slight anemia.
Diagnosis is hard to set because this disease is comparable to "psychogenic potomania". This is a behavioral disorder that causes the urge to drink an enormous amount of fluid, even greater than the one absorbed in case of diabetes insipidus. The polyuria is also more severe than in case of diabetes insipidus. Clinically, the onset of potomania is often brutal. The patient sometimes presents with psychiatric disorder after an emotional shock and the urination varies from one day to another. None of these signs is clear, but an accurate diagnosis is still essential, of course, because the course of treatment is obviously very different.

 

Reviews and analyzes

The doctor may ask for dynamic tests.

The water deprivation test helps determine whether there is still room for secretion of ADH hormone. The test is performed in hospitals to prevent dehydration. The patient’s urine is weighed and then they are laid in bed. Their tension is measured every 15 minutes and their urine is collected in numbered jars every 30 minutes. The test ends when the patient shows signs of discomfort: anxiety, dry mucous membranes, rapid pulse, decreased blood pressure and weight. The combination of dehydration and the inability of the kidney to concentrate the urine despite the abolition of drinks allows for an accurate diagnosis. It goes without saying that this test cannot be completed if the patient suffers from diabetes insipidus.

The tests can indicate vasopressin or DHA deficiency.

Other tests may also be performed. The most widely used tests target the antidiuretic property. A differential diagnosis may be difficult in the event of potomania. Prolonged potomania can inhibit the secretion of ADH hormone (induced diabetes insipidus). Diabetes insipidus can be cured but those who have the habit of drinking lots of fluids will continue doing so and therefore will present excessive urination (self-sustained diabetes insipidus). Their primitive thirst center may also be disrupted (by a lesion or tumor in the hypothalamus). Sometimes the doctor performs a deconditioning test and psychotherapy. The goal is to persuade the patient to drink less, to adopt a sodium diet and possibly take an antidiuretic drug, which is gradually replaced by a placebo. Then, there will be a decrease in the antidiuretic hormone secretion.

Causes and risk factors

The causes of diabetes insipidus are usually the following: sequelae of head trauma, meningitis, encephalitis or neurosurgical interventions in the hypothalamic region, pituitary brain tumor (craniopharyngioma, metastatic lung, breast or colon cancer), tuberculosis, sarcoidosis, histiocytosis X, Schuller-Christian disease, Wegener granulomas and sometimes a systemic disease (collagenosis) in the pituitary-hypothalamic area.
An MRI examination is essential to find the cause of the disease. Idiopathic diabetes insipidus (i.e. no cause found - about 30% of cases) is a family illness.

Nephrogenic diabetes insipidus

There is also a disease called nephrogenic diabetes insipidus, which can be hereditary (transmitted by females and manifesting only in humans) or secondary to chronic kidney disease (pyelonephritis, myeloma, amyloidosis...) or caused by a drug like lithium, aminoglycosides, methoxyflurane anesthesia.
In infants, nephrogenic diabetes can result in severe dehydration, fever, vomiting and seizures.

Treatment

The course of treatment obviously depends on the cause. However, the patient must not dehydrate or hyper-hydrate and should have a low salt diet. It is imperative that the cause is treated.

Desmopressin is an analogue of ADH with a very powerful action. It is usually administered endonasally twice a day.