Could Knee Pain Be First Sign of Lung Cancer?

Uncommon symptoms are common with lung cancer

In very rare instances, knee pain can be a sign of lung cancer. This surprising symptom may be caused by unusual complications associated with lung cancer, or it may occur if a tumor spreads to connective tissue areas.

While it's more likely that knee pain is related to injury, joint disease, or other common causes, the fact that lung cancer could affect your knees is a reminder that you need to be insistent that doctors check every possible scenario to identify the root of a medical issue. Also, if you know you have a high risk of lung cancer because of smoking, genetics, or environmental exposure, be aware of any new health concerns like joint pain. You may want to discuss the pros and cons of a cancer screening with your doctor even if you don’t have any of the “typical” signs of lung cancer.

 Paraneoplastic Syndrome

People with lung, ovarian, lymphatic, or breast cancer have a high risk of developing a condition called paraneoplastic syndrome in which cancerous tumors cause organ or tissue damage that can trigger a number of unusual disorders. It affects approximately 10% of all people with lung cancer.

Paraneoplastic syndromes are thought to happen when cancer-fighting antibodies or white blood cells (known as T cells) mistakenly attack normal cells in the nervous system.

Paraneoplastic syndrome can interfere with a wide range of organ functions. When it develops from lung cancer, it’s likely to affect neurologic, endocrine, dermatologic, rheumatologic, hematologic, or ophthalmological function. It may also cause kidney problems and abnormal blood clotting.

The two most common problems associated with paraneoplastic syndrome in lung cancer patients are:

  1. Hypercalcemia of malignancy in squamous cell carcinoma, in which high blood calcium levels may cause confusion, nausea, vomiting, abdominal pain, muscle aches, and more.
  2. Inappropriate Antidiuretic Hormone Hypersecretion (SIADH) in small cell lung cancer, which results from the body holding on to too much water, causing sodium levels to drop dangerously low.

Metastases

While lung cancer is most commonly associated with metastases to the brain, lymph nodes, liver, and adrenal glands, it can spread almost anywhere, including the synovial tissue. Synovial tissue is the connective tissue that makes up the protective membranes surrounding the body’s joints.

When cancer metastasizes to these areas of the body, the cancer is most often originally from lung adenocarcinomas, and the joints most likely to be affected are the knees.

When the knee is impacted in this way, symptoms may include:

  • pain
  • swelling
  • an inability to bear weight
  • An inability to straighten the knee

Surgery to remove the entire tumor is usually the first course of treatment for cancer in the synovial tissue. Chemotherapy may also be recommended to ensure all malignant cells are eliminated. 

Hypertrophic Pulmonary Osteoarthropathy (HPOA)

HPOA is another rare syndrome that may result from lung cancer and could cause the first signs of the disease. Substances secreted by lung cancer tumors or substances made by the body in response to the presence of the tumors cause swelling and inflammation.

Signs of HPOA may include:

  • clubbing, swelling of the ends of the fingers
  • koilonychia, spoon-shaped nails
  • painful inflammation and swelling in the knees, ankles, wrists, and elbows

Once the tumor is removed, the knee pain or other symptoms related to HOA should improve. Treatment may also include nonsteroidal anti-inflammatory drugs (NSAIDs) or bisphosphonates, medications typically prescribed to treat osteoporosis.

Knee Pain as a Symptom of Lung Cancer

Both monoarthritis (pain in one joint) and polyarthritis (pain in multiple joints) have been identified as possible signs of lung cancer. Often, these symptoms are misdiagnosed, however.

The connection between knee pain and lung cancer can easily be missed because the rate of arthritis problems occurring with lung cancer are very low. 

  • Arthritis symptoms due to paraneoplastic syndrome occur in approximately 0.24% of lung cancer patients. 
  • HPOA incidents among lung cancer patients range from 0.72% to 17%.
  • Researches have only reported 48 cases of synovial metastasis, and only a fraction of those incidents are related to knee pain.

Similar to shoulder pain caused by lung cancer, knee pain is more commonly related to other causes and rarely a symptom of lung cancer. It’s only with continued testing and a willingness to get to the root cause of the problem that the connection between knee pain and lung cancer may be found

If you have rheumatoid arthritis (RA), your knee pain is likely related to your arthritis. However, you should discuss your risk of lung cancer with your doctor. Those with RA are eight times more likely to develop interstitial lung disease, which puts you at risk for lung cancer.

Diagnosis

When patients who have not been diagnosed with lung cancer present with knee pain, doctors first look for the obvious causes of joint disease or injury. The connection between knee pain and lung cancer may only be found if you continue to insist on testing to find the cause of pain that persists or when the discomfort spreads to other joints.

Doctors may be prompted to test for lung cancer for the following reasons:

  • Signs of paraneoplastic syndromes, such as clubbing, may lead your doctor to suspect lung cancer, but if there's no history of smoking, it may take repeated treatments for joint-related disease to fail before tests for lung cancer are ordered.
  • With HPOA, x-rays taken to investigate the cause of knee pain may show damage to the long bones of the leg, which could raise a flag that you may have a tumor.
  • Synovial tissue metastases may be suspected if the knee joint pain doesn’t respond to treatment for inflammation and rheumatoid factor test are negative (showing the problem isn’t related to an autoimmune diseases such as RA).

CT scan of the chest and a biopsy of the lung may be ordered to confirm a cancer diagnosis.

Treatment Options

 Once lung cancer is identified as the cause for the knee pain, treatment will focus on removing or reducing the tumor via surgery, chemotherapy, and/or radiation.

The type of surgery and the course of chemotherapy and radiation will depend on where the tumors are located. The disorders that cause knee pain are usually related to tumors outside the lung. Your doctor will follow protocols based on where the cancer lived

Your doctor may also try to decrease your body’s autoimmune response with steroids, high-dose intravenous immunoglobulin, or irradiation.

A Word From Verywell

The profile of a lung cancer patient has changed over the years. Today, young, non-smoking women are more likely to develop the disease in the form of lung adenocarcinoma. These cancers grow in the outer regions of the lungs undetected for a long time. You may not have classic symptoms of lung cancer until these tumors are large, or you may have vague symptoms that are easily ignored such as shortness of breath, unintended weight loss, and simply a vague sense of being unwell. If knee pains or any other unusual health symptoms arise, they might be a sign. Discuss any new problems with your doctor; it's better to get it checked out and determine the root cause than let it go and face an advanced-stage disease down the road.

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