Why Does Lung Cancer Cause SIADH?

Your body has special hormone called anti-diuretic hormone (ADH) that is so essential to help regulate the balance of fluid. If there is something goes awry with this hormone, some complications can occur. One of them is a condition called syndrome of inappropriate antidiuretic hormone (SIADH), which also can occur in people with lung cancer.

Hormones are special substances which play a key role in regulating many processes and mechanisms in the body. These are produced in glands, released into the bloodstream and distributed around the body through the flow of blood to their target organs.

They are so important to help coordinate the functions of lots of cells and organs – including for the balance of water /fluid which is reabsorbed by the kidneys.

The imbalance between the amount of water you lose (through passing urine, evaporation, or sweating) and the amount of water you gain (from your diet and water coming from cellular respiration) can be serious. For instance, this imbalance can cause cell damage.

So the amount of water in the body should be controlled as well. To keep this balance, your body release ADH. How does it work?

When your body has too much water

The brain, especially hypothalamus, can detect the amount of fluid – whether there is enough, too much water, or lack of water in the blood. To regulate the fluid balance in the body, hypothalamus gives message to special gland called pituitary gland to release ADH.

ADH is released into the bloodstream and travels to the kidneys, affecting the tubules to reabsorb more water.

More ADH released into the blood means more water will be reabsorbed by the kidneys. The opposite effect occurs if there are low ADH hormones in the blood.

When hypothalamus detects too much water, pituitary gland will produce and release less ADH into the bloodstream – or sometimes it doesn’t release ADH at all for a while. As a result, the kidneys are less likely to reabsorb water and you will pass large volumes of dilute urines (see the following picture, credit to ABPI).

When your body has too little water

Perhaps you have been sweating a lot, or have not drunk adequate water. For this scenario, the body recognizes it for dehydration or there is too little water in the body.

To respond dehydration, hypothalamus sends massage to pituitary gland to make and release more ADH into the bloodstream.

As a result, the kidneys are likely to reabsorb more water and you have a smaller volume of more concentrated urine. You are also likely to feel thirsty and drink more water to restore the balance of water in your body.

It is a group of symptoms that occur when there is too high ADH in the blood. In essence, it can lead to fluid retention in the body. This excess water accumulation can cause electrolyte imbalance.

The problem can also lead to a condition called hyponatremia, especially dilutional hyponatremia in which the level of sodium remains normal but the fluid increases so thus there will be too low sodium in the blood.

SIADH can be serious condition. Even if it occurs suddenly, it can be life-threatening.

Symptoms

The symptoms are likely to be noticed clearly when SIADH has become severe. These are also dependent on how far the sodium level drops in the blood.

The signs and symptoms can vary. At first, these may be vague or mild.  These include:

1. Lethargy or fatigue.
2. Nausea or /and vomiting.
3. Headache or/and irritability.
4. Muscle cramps or tremors.
5. Worsening mental status or changes in personality such as confusion, combativeness, or hallucinations.
6. Seizure or even coma.

Since some of these symptoms can be quite vogue, it’s important to not make a diagnosis on your own. Always talk with your doctor for a diagnosis.

Causes

Typically, SIADH is common in people with heart diseases (especially heart failure) or other diseases that affect hypothalamus. Other causes include:

1. Inflammation of the brain such as encephalitis.
2. Meningitis (inflammation of the membranes covering the brain & spinal cord).
3. Head trauma.
4. GBS (Guillain-Barré syndrome), a neurological condition that can lead to muscle weakness, temporary paralysis, and pain. Fortunately, this disorder is reversible.
5. Thyroid problem (especially such as parathyroid hormone deficiencies).
6. HIV infection.
7. Hereditary causes.
8. Psychosis, a serious mental disorder.
9. Side effects of certain medications. For instance, sometimes a surgery may cause damage to pituitary gland or hypothalamus.

Cancer of the brain can affect hypothalamus. Even certain cancer elsewhere in the body can also lead to SIADH. These cancers include; lung cancer, lymphoma, neck and head cancers, mesothelioma, Ewing sarcoma, certain thymus cancer, stomach cancer, pancreatic cancer, duodenum cancer, uterine cancer, prostate cancer, and bladder cancer.

Most cancers are life-threatening. But lung cancer is mostly found at advanced stages. That’s why it is the top leading cancer that causes death. The common complications include:

1. Feeling of breathless (shortness of breath). Cancer in the lung can block the major airways, causing shortness of breath.
2. Persistent cough or coughing up blood. The cancer can cause internal bleeding in the airway.
3. Pain, especially chest pain. However, there is also a chance for cancer to cause pain in other parts of the body (see more in here).
4. Pleural effusion, the excess accumulation of fluid in the chest. Cancer in the lung can cause fluid build-ups that accumulate in the plural space.
5. The worst scenario is when the cancer has spread to other parts of the body.

In some cases, lung cancer (both non-small cell and small cell carcinoma) can cause SIADH for several reasons. These may include: