SIADH - Syndrome of inappropriate secretion

Syndrome of inappropriate ADH secretion (vasopressin or antidiuretic hormone) are symptoms derived from excessive secretion of this hormone by the hypothalamus. It is abbreviated as SADH.

How is it produced?

Excessive ADH secretion causes decreased levels of sodium in the blood (hyponatremia). Hyponatremia is due to the inability of the kidney to eliminate water. As a consequence, the urine will be excessively concentrated and, however, the blood will be very dilute. This will cause all the ions and components of the blood to be in lower concentration in the blood, and especially sodium.

The causes that may be involved in the excessive secretion of ADH are multiple:

• Tumors or neoplasms that arise outside the hypothalamus but are capable of making ADH.
• Non-malignant lung diseases: tuberculosis, lung abscess, pneumonia, asthma, etc.
• Some drugs are capable of stimulating the production of this hormone by the hypothalamus; This is the case of nicotine, chlorpropamide, carbamazepine, antidepressant drugs and some drugs used in the treatment of cancer.
• Neurological diseases: Guillain-Barré syndrome, multiple sclerosis, meningitis, etc.
• Head trauma.

It is important to note that not all individuals who, for example, have asthma, or are taking carbamazepine, will develop this syndrome.

Symptoms

The symptoms of this disease will depend on two elements: first, on the levels of sodium in the blood at the time of diagnosis and, second, on the speed with which the levels of sodium in the blood fall.

Thus, in cases in which the decrease in sodium is slow and progressive, or in those cases in which the sodium levels, although low, are at moderate levels (more than 130 mEq / l), the symptoms are mild or null. .

In cases where sodium levels drop to severe levels (less than 120 mEq / l), or have developed rapidly, neurological symptoms appear: agitation, confusion, irritability, decreased level of consciousness, seizures and coma. .

Diagnosis

The diagnosis goes through the determination of sodium in the blood. We will find low or very low sodium levels (hyponatremia). However, there are other causes of hyponatremia, in addition to the syndrome of inappropriate ADH secretion.

Therefore, to reach a correct diagnosis other causes must be ruled out. Thus, situations of increased blood sugar, adrenal insufficiency and hypothyroidism can cause a decrease in sodium in the blood. In SIADH, the so-called osmolarity in the blood (calculated by the levels of sodium, potassium and sugar in the blood) is decreased, and there will also be a highly concentrated urine, with much excretion of sodium in the urine and an increased osmolarity in urine (greater than the of the blood). On the other hand, in SIADH, there is characteristically no fluid retention in the feet (edema), nor is there low blood pressure, nor signs of dehydration.

Treatment

Treatment may be aimed at correcting the cause of the excess ADH secretion, if known. For example, drugs suspected of being involved should be removed, possible infections addressed, or the tumor removed. However, sometimes the cause of SIADH is not known, or the cause cannot be solved. Thus, in most cases the treatment will be aimed at improving sodium levels and increasing the concentration of the blood (osmolarity) and reducing that of the urine.

In these cases, a restriction of total fluid intake to less than 800-1000 ml per day will be indicated. Low doses of furosemide can also be used (a powerful diuretic that is characterized by eliminating more water than sodium in the urine and thus succeeding in diluting the urine and concentrating the blood). If, on the other hand, these measures are not achieved, correcting sodium can be used drugs that act either by inhibiting the secretion of ADH, or by blocking its action. These drugs include demeclocycline, 150 to 300 mg orally three or four times a day, or fludrocortisone, 0.5 to 0.2 mg orally twice a day.

In acute cases of rapid onset, with greatly decreased sodium levels, and with neurological alterations, intravenous treatment based on sodium-rich serum should be instituted by vein to raise sodium levels to levels considered safe (above 120 mEq / l). However, this treatment must be carried out slowly and in a hospital setting, since an excessively rapid correction of sodium levels can cause a serious disease called «central pontine myelinolysis» that can cause permanent neurological losses.

Precautionary measures

There are no measures to prevent its appearance. Just resorting to blood tests in people with an acute illness or with trauma or brain injuries.