The Dangerous Link Between Lung Cancer and Hyponatremia

For patients navigating a lung cancer diagnosis, as well as those caring for them, abnormal sodium levels can raise important questions about what is happening inside the body. Hyponatremia, a condition characterized by low blood sodium, is relatively common for some types of lung cancer, affecting between 25% to 47% of lung cancer patients. But this comorbidity should not be ignored as it may signal that something is seriously wrong. Is it a side effect of treatment, a sign that the tumor is affecting hormone regulation, or a modifiable condition that could influence symptoms, quality of life and even cancer outcomes?

We spoke with Dr. Amit "Bobby" Mahajan, Medical Director of Inova Interventional Pulmonology and Complex Airway Disease Program, about the relationship between lung cancer and hyponatremia. He weighed in on how knowing the basics of this common condition can help patients and healthcare providers recognize its causes, identify when intervention is needed, and make informed decisions that support overall cancer care. 

What Causes Hyponatremia?

Sodium is a natural occurring electrolyte that the body needs to function normally. So, when sodium levels are irregular and the level of circulation in the blood is low, hyponatremia occurs. “The low levels are commonly due to fluid retention and dilution of sodium,” Dr. Mahajan explained.

For cancer patients, hyponatremia is often the result of a Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH). Patients with SIADH have a body that is making too much of the anti-diuretic hormone (ADH). In a healthy body, ADH helps the kidneys manage the amount of water and salt in the body, controlling blood pressure. But for people with SIADH, the body continued to release ADH unnecessarily, making the kidneys hold more water and lower sodium levels.

“Disturbances in sodium within the body can result in multiple symptoms including altered mental status, nausea, vomiting, muscle cramps, and, in severe cases, seizures,” Dr. Mahajan explained.  

Unfortunately, certain common lung cancer chemotherapies and immunotherapies have been linked to developing hyponatremia. So, if any of these changes occur, Dr. Mahajan suggests seeking immediate medical attention. “While a variety of medical issues can cause such symptoms, patients with lung cancer, especially small cell lung cancer, have a low threshold for suspecting hyponatremia secondary to SIADH.”  

How is Hyponatremia Diagnosed and Treated?

Hyponatremia is relatively easy to diagnose, as it only requires a basic serum sodium level test done via blood draw to determine if something is off. Additional blood and urine tests are needed to determine if SIADH is the underlying driving factor. Further testing of the adrenal glands, thyroids, and kidneys may also be needed to confirm that SIADH is a complication of lung cancer.

“Patients with small cell lung cancer have the highest incidence of SIADH,” Dr. Mahajan said. “While treatments for SIADH are available, this condition can lead to prolonged hospitalizations, poor functional capacity, and negative effects on survival, which is why it needs to be addressed as soon as possible.”

In fact, acute hyponatremia can be a medical emergency that often requires fluid restriction and an IV of hypertonic saline solution in a hospital setting. This must be carefully monitored, however, because “correcting sodium levels slowly is essential; otherwise, patients are at risk of neurologic damage.”

For milder cases, patients can be treated at home with fluid restriction and sodium replacement. However, Dr. Mahajan stress that “a doctor should always be involved in the management of hyponatremia as this disorder can sometimes be life threatening if not managed appropriately.”

For cancer patients specifically, the protocol is a little more complex. Additional medications are available for the treatment of cancer-related hyponatremia, that help the kidneys regulate fluid retention. “And, ultimate treatment of the underlying cancer helps prevent the recurrence of SIADH,” he concluded.

Since hyponatremia has been found to be a predictor of survival rates for small-cell lung cancer patients, it is important it never be ignored. Learn more about underlying health conditions that can make lung cancer treatment more complicated on our website.