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Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Overview

Highlights

  1. SIADH causes the body to retain excess water.
  2. Excessive levels of antidiuretic hormones in the body cause SIADH.
  3. SIADH is most often associated with lung cancer.

Antidiuretic hormone (ADH) is produced by an area of the brain called the hypothalamus. This hormone is stored in and released by the pituitary gland. ADH controls how your body releases and conserves water.

When ADH (also called vasopressin) is produced in excess, the condition is called syndrome of inappropriate antidiuretic hormone (SIADH). This overproduction can occur in places other than the hypothalamus.

SIADH makes it harder for your body to release water. Additionally, SIDAH causes levels of electrolytes, like sodium, to fall as a result of water retention. A low sodium level or hyponatremia is a major complication of SIADH and is responsible for many of the symptoms of SIADH. Early symptoms may be mild and include cramping, nausea, and vomiting. In severe cases, SIADH can cause confusion, seizures, and coma.

Treatment usually begins with limiting fluid intake to prevent further buildup. Additional treatment will depend on the cause.

Another name for the syndrome is “ectopic ADH secretion.”

Causes of SIADH

Causes

A variety of conditions can trigger abnormal ADH production, including:

  • brain infections
  • bleeding in or around the brain
  • head trauma
  • hydrocephalus
  • Guillian-Barre syndrome
  • multiple sclerosis
  • infections including HIV and Rocky Mountain spotted fever
  • cancers of the lung or gastrointestinal or genitourinary tract, lymphoma, sarcoma
  • lung infections
  • asthma
  • cystic fibrosis
  • medications
  • anesthesia
  • hereditary factors
  • sarcoidosis

Symptoms of SIADH

Symptoms

SIADH makes it difficult for your body to get rid of excess water. This causes a buildup of fluids as well as abnormally low sodium levels.

Symptoms may be mild and vague at first, but tend to build. Severe cases may involve these symptoms:

  • irritability and restlessness
  • loss of appetite
  • cramps
  • nausea and vomiting
  • muscle weakness
  • confusion
  • hallucinations
  • personality changes
  • seizures
  • stupor
  • coma

Diagnosing SIADH

Diagnosis

Your doctor will ask for your complete medical history and current symptoms. Your doctor should know whether you are taking any over-the-counter or prescription medications or supplements. Diagnosis usually begins with a physical exam. Often, a urine sample is also required.

Blood tests, specifically one called an ADH test, can measure circulating ADH levels in the blood, but it’s very difficult to obtain an accurate level. According to the University of Rochester Medical Center, normal values for ADH range from 0-5 picograms per milliliter. Higher levels could be the result of SIADH. Most cases of SIADH are accurately diagnosed using serum and urine sodium and osmolality values as well as clinical presentation.

Following diagnosis of SIADH, the next step will be to identify the condition that caused it to occur.

Treatment and prognosis for SIADH

Treatment

The first line of treatment is to limit fluid intake to avoid further buildup. Medications may include those that can reduce fluid retention, such as furosemide (Lasix), and those that can inhibit ADH, like demeclocycline.

Your prognosis will depend on the cause of SIADH. Any underlying medical conditions must be treated.

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