= =

Sodium is more than an ingredient you have to watch in your diet — it’s also a key nutrient your body needs to function properly. Having hyponatremia, or low sodium levels, could lead to serious complications. People living with lung cancer are at risk of developing hyponatremia, so it’s important to know what symptoms to look out for.

In this article, we’ll cover what hyponatremia is, what it looks like, and how your doctor may treat it. We’ll also discuss ways your doctor can treat hyponatremia to avoid symptoms and complications.

What Is Hyponatremia?

Hyponatremia is an electrolyte disorder caused by sodium levels that are too low. Electrolytes are charged elements that your body needs to perform normal functions. You may see sodium written as “Na+” due to its positive charge. Other examples of electrolytes include potassium, calcium, and magnesium.

Normally, your serum (blood) sodium levels should be between 135 and 145 milliequivalents per liter (mEq/L). You have hyponatremia if your levels fall below 135 mEq/L. Some doctors also define hyponatremia as mild, moderate, or severe, depending on how low your sodium levels are.

How Does the Body Control Sodium Levels?

Sodium is key for helping your nerves send signals from your brain to the rest of your body. It also helps muscles contract (tighten) and relax to control your movements. Your kidneys need a balance between sodium and potassium to regulate your body’s fluid balance as well.

Sodium levels in the bloodstream are controlled by antidiuretic hormone (ADH). This hormone is also known as vasopressin or arginine vasopressin. When your sodium or blood pressure levels fall, the kidneys make an enzyme called renin. This activates the pituitary gland in your brain to release ADH. The pituitary gland is a tiny gland at the base of your brain that helps control important body activities by sending out hormones.

Renin also triggers the adrenal glands on top of your kidneys to release the hormone aldosterone. Together, ADH and aldosterone tell the kidneys to hold on to sodium. The more sodium in your body, the more water it holds on to. This raises your blood pressure.

Hyponatremia in Lung Cancer

You likely know that too much sodium — especially from your diet — can lead to high blood pressure and heart problems. However, sodium levels that are too low can also cause health problems in people with lung cancer.

Studies show that hyponatremia is the most common electrolyte abnormality associated with lung cancer. Researchers believe that 25 percent to 47 percent of people with lung cancer develop low sodium levels, according to the journal Translational Lung Cancer Research. There are two main types of lung cancer — non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Hyponatremia is much more common in those with SCLC.

SIADH Leads to Hyponatremia

People with SCLC are at an increased risk of developing the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This is a type of paraneoplastic syndrome (immune system response to cancer) that affects your hormone levels.

If you have SIADH, a lung cancer tumor releases extra ADH into your bloodstream. This means the body holds on to too much water. As your fluid levels rise, sodium concentrations in the blood dilute down. If you don’t consume more sodium, you’re at risk of developing hyponatremia.

Lung Cancer Metastasis Can Cause Low Sodium Levels

In stage 4 lung cancer, cancer cells break away and metastasize (spread) to other parts of the body. Common places for metastatic lung cancer to form include the brain, liver, bones, and adrenal glands. Studies from Translational Lung Cancer Research show that brain metastases may lead to low sodium levels. Specifically, they can cause cerebral salt wasting — loss of sodium caused by diseases in the brain and spinal cord.

Lung Cancer Treatments Raise the Risk of Hyponatremia

All medications come with side effects, including cancer therapies. Some chemotherapy drugs affect the kidneys more than others. This may increase your risk of hyponatremia. For example, one study showed that people treated with cisplatin were twice as likely to have low sodium levels as those taking carboplatin.

Other reports have found that immunotherapies for lung cancer can also lead to hyponatremia. Immunotherapies are protein drugs that activate the immune system to fight cancer. Nivolumab (Opdivo) has been shown to interfere with adrenal gland function and cause low sodium levels.

Symptoms of Hyponatremia

If you have mild hyponatremia, you likely won’t notice any symptoms. Moderate hyponatremia (125 to 129 mEq/L) can cause:

• Headache
• Nausea and vomiting
• Fatigue or drowsiness
• Confusion or hallucinations (seeing or hearing things that aren’t real)
• Changes in mood, like irritability or restlessness
• Muscle cramps, weakness, or spasms (uncontrollable movements)

Severe hyponatremia (115 to 120 mEq/L) can lead to life-threatening complications such as seizures or coma. Respiratory arrest can also occur, meaning a person stops breathing. Doctors can usually reverse hyponatremia symptoms with treatment — however, it may cause permanent brain damage.

It can be difficult to tell symptoms of lung cancer versus hyponatremia apart. For example, you may be fatigued from:

• Your lung cancer treatment, like chemotherapy, radiation therapy, or targeted therapy
• Lung cancer
• Hyponatremia or SIADH

Certain cancer medications can also make you nauseous or trigger vomiting. Having abnormally low sodium levels may make these symptoms even worse. If you notice any new or worsening symptoms, be sure to talk to your oncologist (cancer specialist). They can run blood tests to check your sodium levels.

Hyponatremia and Prognosis With Lung Cancer

Did you know that your sodium levels may help predict your prognosis (outlook) with lung cancer? Researchers have found that people with hyponatremia are more likely to:

• Be hospitalized for a while to treat low sodium levels
• Reschedule chemotherapy treatments due to side effects
• Have worse performance status, meaning you have a harder time completing daily activities like walking and working
• Have a lower quality of life

Some studies have also shown that people with lung cancer and hyponatremia may have worse overall survival (OS). Researchers use OS to describe the percentage of people with cancer alive after a certain period of time. One review of multiple studies found that people with NSCLC and hyponatremia have worse OS than those with SCLC.

Management of Hyponatremia With Lung Cancer

If you develop hyponatremia while living with lung cancer, your doctor may suggest some treatments. Your exact treatment plan will depend on your sodium levels and symptoms.

If you have mild hyponatremia and no symptoms, your doctor may recommend fluid restriction. You’ll limit how much water and other fluids you eat and drink throughout the day. Less fluid means an increase in serum sodium concentration. You may also be prescribed a diuretic. These medications help your kidneys remove extra fluid and get rid of it as urine.

People experiencing symptoms of hyponatremia are usually treated with hypertonic saline. “Hypertonic” means there is a higher salt concentration in the saline than in the bloodstream.

The U.S. Food and Drug Administration (FDA) has also approved two medications for hyponatremia due to SIADH. Your doctor may prescribe tolvaptan (Samsca) or conivaptan (Vaprisol) to help raise your sodium levels. These medications help the kidneys get rid of extra water as urine.

Find Your Team

MyLungCancerTeam is the social network for people with lung cancer and their loved ones. On MyLungCancerTeam, more than 13,000 members come together to ask questions, give advice, and share their stories with others who understand life with lung cancer.

Have you been diagnosed with hyponatremia while living with lung cancer? How has your doctor treated it? Share your experience in the comments below, or start a conversation by posting on your Activities page.