Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a common complication of small cell lung cancer (SCLC). It can cause many symptoms related to low sodium or other electrolyte imbalances.

SIADH involves the overproduction of antidiuretic hormone (also called vasopressin).

SIADH can develop as a result of any condition that causes your pituitary gland to make too much antidiuretic hormone. It can also occur when tissues that don’t normally produce this hormone start producing it.

Some tumors, particularly SCLC tumors, can lead to SIADH due to the overproduction of antidiuretic hormone from cancer cells. SIADH can occur before or after a cancer diagnosis.

Read on to learn more about the connection between SIADH and SCLC.

SIADH occurs in an estimated 10% to 45% of people with SCLC at some point in the course of their disease.

It develops as a result of abnormally high levels of antidiuretic hormone. This hormone is normally produced by your hypothalamus and released by your posterior pituitary gland (a pea-size gland found at the base of your brain).

SIADH can occur if you have a condition that causes excess release of antidiuretic hormone from your pituitary gland or if tissues that normally don’t produce antidiuretic hormone start creating it.

SCLC can lead to excess antidiuretic hormone production

SCLC is the most common type of tumor that leads to excess antidiuretic hormone production. A potential complication of SIADH is hyponatremia (abnormally low sodium levels).

Potential symptoms of hyponatremia include:

If you have SCLC, SIADH can occur if cancer cells produce excess amounts of antidiuretic hormone, resulting in high levels of the hormone circulating in your blood.

The production of antidiuretic hormone by cells that don’t normally produce it is known as ectopic antidiuretic hormone production.

SIADH falls into a group of conditions called paraneoplastic syndromes.

Paraneoplastic syndromes are collections of symptoms that develop in people with cancer but are unrelated to the direct spread of the cancer cells. Instead, the symptoms are caused by abnormal overproduction of molecules such as:

  • hormones
  • autoantibodies
  • inflammatory molecules called cytokines
  • peptides (short chains of amino acids)

SCLC and other paraneoplastic syndromes

SCLC can lead to one of several other paraneoplastic syndromes, such as:

  • Cushing syndrome from the secretion of adrenocorticotropic hormone: Cushing syndrome from the secretion of adrenocorticotropic hormone occurs when cancer cells produce excess adrenocorticotropic hormone. This hormone leads to the overproduction of cortisol, causing symptoms such as:
    • weight gain
    • wide, purple stretch marks
    • thin arms and legs
    • a round face
    • increased fat around the base of your neck
    • a fatty hump in your upper back
    • easy bruising
    • weak muscles
  • Paraneoplastic cerebellar degeneration: This is an autoimmune reaction that affects a part of your brain called the cerebellum. It’s characterized by:
    • weakened muscles in your limbs
    • trouble speaking and swallowing
    • dementia
    • involuntary rapid eye movements
    • tremors
    • problems with cognitive or emotional regulation
  • Lambert-Eaton myasthenic syndrome: Lambert-Eaton myasthenic syndrome is an autoimmune reaction that targets nerves and may cause:
    • muscle aches
    • fatigue
    • difficulty with walking, lifting objects, or performing other movements
    • drooping eyelids, blurred vision, or dry eyes
    • erectile dysfunction
    • progressive muscle weakness

Symptoms of paraneoplastic syndromes can develop before or after an initial cancer diagnosis.


Can SIADH appear in people without small cell lung cancer?

SIDAH can occur as a result of any condition that causes excessive release of antidiuretic hormone from your pituitary gland or any condition that causes the release of this hormone from cells that don’t normally produce it.

Many other cancers can cause SIADH, including:

A doctor may diagnose SIADH before or after you receive an SCLC diagnosis.

If you have not yet received a cancer diagnosis, your initial tests will usually include:

  • a review of your personal and family medical history
  • a review of your symptoms
  • a physical exam
  • blood and urine tests to check your electrolyte levels

Blood and urine tests may reveal abnormal levels of sodium and other electrolytes, which can suggest SIADH or another problem with your antidiuretic hormone levels.

If your doctor suspects a tumor, you might receive other tests, such as chest X-rays or a CT scan, to look for signs of lung cancer.

The same tests are used to diagnose SIADH if you already have a cancer diagnosis.

Your doctor will likely want to perform most of these tests even if you don’t have symptoms of SIADH since people with SCLC are at such a high risk of developing hormone problems.

The main treatment goal for SIADH is to correct your sodium levels.

Mildly to moderately low sodium levels may be treatable by limiting your fluid intake until your sodium levels return to normal.

For chronic hyponatremia, you may need to take medications such as tolvaptan to block the production of antidiuretic hormone in your body.

In severe cases, you’ll need immediate hospitalization so that you can receive intravenous (IV) saline solution to correct your sodium levels and prevent potential complications.

Treatment options for SCLC include:

SIADH is generally considered a negative prognostic factor for people with people SCLC. This means it’s associated with a worse outlook.

The 5-year relative survival rates for SCLC from 2014 to 2020 in the United States were:

Stage at diagnosis5-year relative survival rate
localized33.3%
regional19%
distant3.9%
all stages8.6%

SIADH is a common complication of SCLC that involves abnormally high levels of antidiuretic hormone. It can cause many symptoms, including fatigue, nausea, and even seizures.

Many types of cancer can cause SIADH, but people with SCLC are at the highest risk.

Treatment may consist of reducing your fluid intake, taking medications to increase your sodium levels, or receiving emergency treatment to prevent serious side effects.