SYNDROME OF INNAPROPRIATE ADH SECRETION (SIADH)
The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a syndrome frequently encountered in hospitals, particularly in patients hospitalized for problems in central nervous system (CNS). As the name suggests, is a syndrome characterized by an excessive release of antidiuretic hormone (ADH or vasopressin) from the posterior pituitary. This results in hyponatremia, and sometimes fluid overload.
The antidiuretic hormone (ADH) is synthesized by neurons of the hypothalamus and stored in the pituitary. It exerts its action in the kidneys by allowing water reabsorption by the collecting duct and thus the concentration of urine.
Antidiuretic hormone secretion is stimulated by two factors: the increase in plasma osmotic pressure (force exerted on both sides of the cell membrane of capillary blood vessels) and the drop in pressure of the blood volume circulating (hypovolemia).
Antidiuretic hormone deficiency is responsible for diabetes insipidus, condition characterized by polyuria (emission of large amounts of urine) and polydipsia (increased thirst and compelling). This deficit can be offset by the administration of oral desmopressin.
Hypersecretion inappropriate antidiuretic hormone, or Schwartz-Bartter syndrome, is characterized by lower levels of sodium in the blood and reducing urine; this syndrome is often linked to the existence of a tumor (most often cerebral and pulmonary) and is called paraneoplastic syndromes. Drugs ADH antagonists, by blocking its receptors, treat this syndrome and edema associated with congestive heart failure.
Summary
1 Pathophysiology
2 Clinic
3 Survey etiological
4 Treatment
5 Differential Diagnosis
Part 6
Pathophysiology
Normally, the antidiuretic hormone (ADH) controls the osmolar concentration of the organism. It maintains a stable concentration osmolar through the volume of water contained in the human body. DHA induces the retention of “pure” water at the distal convoluted tubule in the kidney. The retained water dilutes the excess osmoles that stimulated the secretion of antidiuretic hormone.
The mechanisms of secretion of ADH outside its usual controls are imperfectly understood. Tissues become capable of secreting a hormone similar to ADH in large quantities; is the case of cancer and bronchopulmonary infections.
Clinical
There is no specific sign of this syndrome. The major signs are those of the intracellular overhydration or hyponatremia, nausea, vomiting, confusion and behavioral problems. In cases of severe hyponatremia, coma and convulsions are common.
Etiology
Head injury
Cancers
Lung cancer (including small cell lung cancer)
Lymphoma, Hodgkin’s disease
Infections
Brain abscess
Pneumonia
Lung abscess
Bronchopulmonary aspergillosis
Malignant pertussis
Endocrine causes
adrenal insufficiency
Drugs
Chlorpropamide
Cyclophosphamide
Carbamazepine
Idiopathic
Treatment
fluid restriction
loop diuretic
infusion of hypertonic sodium chloride
dedemeclocycline administration or lithium or urea
ADH V2 receptor antagonist
etiological treatment
Differential diagnosis
Addison’s disease
dilutional hyponatremia on congestive heart / liver
myxedema
pseudo-hyponatremia
Tags: SIADH