SIADH- Syndrome of Inappropriate Antidiuretic Hormone Hypersecretion is a condition caused due to excessive secretion of the Antidiuretic Hormone (ADH) also known as vasopressin. This hormone is secreted by supraoptic and paraventricular nuclei in the hypothalamus and finally secreted via the posterior pituitary gland. The main function of the ADH is to regulate the water reabsorption and as a result influences urine concentration. As a consequence, hyponatremia is caused that in turn leads to fluctuation in the sodium concentration in the blood.

The main function of ADH is to control the amount of water reabsorbed by kidneys thus diluting the blood and decreasing the concentration of sodium in the blood. ADH prevents water loss in the kidneys. When water is consumed it is taken up in the blood which causes its dilution. Once this dilution which is also known as plasma osmolality is detected by osmoreceptors in the hypothalamus, ADH secretion is signaled to stop. The inhibition of ADH reduces reabsorption of water by kidneys thereby increasing the urine output. In SIADH (Dilutional Hyponatremia) when the blood water concentration increases ADH secretion is not stopped as a result the sodium in the blood dissolves and sodium concentration is considerably decreased.

SIADH Syndrome Causes:

• It may be caused due to lowered secretion of thyroid hormone, a condition called hypothyroidism.
• Therapeutic agents such as Nonsteroidal anti-inflammatory drugs(NSAIDs) inhibit prostaglandin E2, which impedes vasopressin’s action. SIADH is also caused as a side effect of multiple psychotropic medications.
• It may be caused due to post operative effects on patients hospitalized for injuries to the central nervous system.
• It can be caused due to meningitis or a head injury resulting in Subarachnoid hemorrhage.
• It is also caused due to infections like brain and lung abscess or pneumonia.
• Drugs that majorly cause this condition are : Clorpropamide, Clofibrate, Phenothiazine, Cyclophosphamide, Carbamazepine,  Selective Serotonin reuptake inhibitors (SSRI’s), Methylenedioxymethamphetamine(MDMA).

Symptoms of SIADH Syndrome:

• Hyponatremia
• Confusion
• Nausea
• Altered mood
• Seizures
• Loss of consciousness

Treatment for SIADH Syndrome:

• Restricting fluid intake
• Supply of hypertonic saline
• Drug doses of the following –

Demeclocycline:
This is the most potential inhibitor of AVP action. It used in chronic situations when restricting fluid intake becomes difficult.

Conivaptan:
It is a non-peptide inhibitor of vasopressin receptors which is an antidiuretic hormone. It also used in cases of heart failure other than being used in the treatment of SIADH.

Tolvaptan:
It is used to treat low blood sodium levels associated with SIADH as well as congestive heart failure and cirrhosis. When administered into patients alongwith regular diuretics it increases the excretion of excess fluids and improve blood sodium levels in patients with heart failure without giving rise to side effects like hypotension.

If timely treatment not taken it can lead to two more conditions known as Hypokalaemia and Hypomagnesemia. Severe hyponatremia may cause convulsions or coma. Another hormone called Secretin which is also secreted from the posterior pituitary gland is a neurosecretory hormone that shows abnormal functions during this condition. This condition is referred to by the names of reporters of this diseases namely,  Schwats and Bartter and is occasionally known as Schwats-Bartter syndrome.

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1. by peter last 7:47 am

   can symptoms of SIADH result in other problems or medical conditions?