Syndrome of Inappropriate Antidiuretic Hormone Secretion

What is Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)?

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is a condition in which the body makes an antidiuretic hormone (ADH). ADH helps regulate the kidney excretion of water through the urine to maintain homeostasis. Certain inappropriate conditions or medications can cause the overproduction of the ADH hormone causing the body to retain fluid and lower the blood sodium level by dilution termed “hyponatremia”. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) accounts for approximately one-third of all cases of hyponatremia and can result in brain dysfunction if the low serum sodium level is not corrected.

What are the causes of SIADH?

  • Medication – These include cancer drugs, anti-convulsant, anti-diabetic and antihypertensive drugs.
  • Infection
  • Surgery
  • Brain and spinal cord tumor, injury or infection
  • Cancer: Very common with small cell lung cancer

What are the symptoms of SIADH?

People with SIADH are frequently asymptomatic and symptoms depend on the severity of the hyponatremia. It includes:

  • Nausea and vomiting
  • Headache
  • Fatigue
  • Restlessness and irritability
  • Muscle weakness, spasms or cramps
  • Seizure, coma, and death in severe cases

How to diagnose SIADH?

A detailed medical history and physical examination along with lab tests are required to evaluate the volume status and sodium level in a patient with SIADH. History and physical examination will help rule out other possible causes of excess ADH such as drugs, pain, and cancer. Blood and urine tests are done to measure the sodium and levels and to determine osmolality which is how concentrated are the blood and urine. 

What are the treatments of SIADH?

  • Treatment of the underlying disease
  • Limit fluid intake
  • Salt tablet or IV hypertonic saline: care must be taken not to correct the sodium too quickly
  • Discounting of the medication causing SIADH

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