Syndrome of inappropriate ADH syndrome (SIADH)


ADH (full form of ADH is anti-diuretic hormone or vasopressin) is a hormone produced from posterior pituitary.

Role of ADH

  • Role of ADH is to retain water in the body. It acts at the collecting duct of nephron by inserting water carrying channels in the wall of the collecting duct called aquaporin, through which water is reabsorbed.

Syndrome of inappropriate ADH syndrome (SIADH) is a condition in which excess ADH is produced in the body, as the name of the syndrome suggests.

Various health conditions can cause SIADH.

CAUSES:

1. CNS (central nervous system) causes: tumors in brain, hemorrhage in brain, infection of brain etc.
2. Lung causes: lung tumors, pneumonia etc.
3. Cancerous causes: small cell cancer of lung, carcinoid syndrome etc.
4. Certain drugs: like drugs used for psychosis and depression

What type of electrolyte abnormality occurs in case of SIADH?

  • A condition called euvolaemic hyponatraemia occurs in SIADH.

What is euvolaemic hyponatraemia and how does it occur?

  • Euvolaemic means no change in blood plasma volume since there is not net gain or loss in total body fluid. The cause of euvloaemia is possibly because the same body water is absorbed by nephron tubules instead of getting excreted. Since water volume in the extravascualr space rise due to water reabsorption in comparison to the total body sodium there is a relative increase in body water, hence giving a picture of hyponatraemia.

How does it affect serum or urine osmolarity?

  • Due to increase in water content osmolarity of serum decrease. Urine osmolarity is relatively higher than that of serum as urine volume is less since most of the water gets reabsorbed.

How does this disease condition presents?

  • Generally there are no specific symptoms for SIADH. The condition may be diagnosed while getting investigations done for some other health purpose. Otherwise, symptoms of hyponatraemia may manifest like digginess, confusion, seizures, coma. Symptoms of hyponatraemia depend on the amount of hyponatraemia.

What is the treatment of SIADH?

  • First is to target the cause. If a tumor of lung is the cause treating the cause will help reduce the symptoms of SIADH.

  • A drug called democlocycline is used for treatment sometimes. Democlocycline is a ADH antagonist, don’t allow ADH to act at ADH receptors.

  • Another option is available i.e. to treat with diuretics like loops (e.g. Furosemide) along with salt tablets. (to replace the lost sodium by diuretics through salt tablets).

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