Lung cancer stands as one of the most diagnosed and deadliest cancers worldwide. It originates in the tissues of the lungs, primarily in the cells lining the air passages. Classified into two main types based on the appearance of lung cancer cells under the microscope, these are: non-small cell lung cancer (NSCLC), which is the most common, and small cell lung cancer (SCLC). Factors such as smoking, exposure to second hand smoke, and exposure to certain toxins increase the risk of developing lung cancer. With its reputation for being particularly aggressive and often detected at an advanced stage, early detection and treatment are critical.

Global Prevalence of Lung Cancer

Globally, lung cancer has been recognized as a leading cause of cancer-related deaths, accounting for approximately 18.4% of total cancer deaths in 2018. The World Health Organization (WHO) estimated that in that year, lung cancer was responsible for 1.76 million deaths worldwide [1]. Numerous countries, both developed and developing, have witnessed an increased prevalence, with factors like smoking, urban air pollution, and occupational exposures contributing to the rise.

Shoulder Pain: A Less-Recognized Symptom of Lung Cancer

Shoulder Pain: A Less-Recognized Symptom of Lung Cancer

While persistent cough, shortness of breath, and chest pain are more commonly associated with lung cancer, shoulder pain is a lesser-acknowledged symptom. Especially when linked to tumors in the upper lungs, such as Pancoast tumors, shoulder pain can be an early sign. This pain is not restricted to movement or activity, can intensify at night, and may be indicative of the cancer’s progression, specifically when it invades nearby structures or when distant metastases occur [2]. Unfortunately, because it is less recognized, this symptom can sometimes be overlooked or misattributed to other causes. Recognizing the potential connection between shoulder pain and lung pathology is essential for early diagnosis and improved outcomes.

Anatomy and Physiology of Lung-Shoulder Connection

Anatomy and Physiology of Lung-Shoulder Connection

Description of the Proximity of Lungs to the Shoulder Region

The human lungs are a pair of spongy, air-filled organs located on either side of the chest (thorax), separated by the heart and other mediastinal structures. The apex (or top) of each lung extends superiorly and posteriorly, reaching up into the base of the neck, just behind the clavicle (collarbone). Due to this anatomical arrangement, any disease or pathology affecting the apex of the lung can potentially influence the neighboring shoulder region.

The close proximity between the lung’s apex and the shoulder is why conditions like a Pancoast tumor (a form of lung cancer that is found on apex of the lung) can manifest with shoulder pain. It’s also worth noting that the diaphragm, the primary muscle for respiration, attaches along the lower ribs and spine and plays a role in shoulder mechanics, especially during deep inspiration.

Nerve Pathways and Their Potential Impact

The cervical and upper thoracic spinal cords give rise to the brachial plexus, a network of interlacing nerves (specifically, from the anterior rami of the C5-T1 nerve roots). These nerves converge to form trunks, divisions, and cords before branching off to supply the entire upper limb. This complex lies in close proximity to the apex of the lung, nestled between the anterior and middle scalene muscles in the neck.

Here’s how the lung’s pathology can affect the brachial plexus and related nerve pathways:

Compression: As mentioned, conditions like Pancoast tumors can directly compress or invade the lower components of the brachial plexus, leading to symptoms like pain, tingling, and weakness in the affected arm. This is often termed as “Pancoast syndrome.”

Referred Pain: Diseases or pathologies of the lung, especially at its apex, can cause pain that is perceived in the shoulder or upper arm. This is due to the overlapping sensory nerve distribution in these regions.

Phrenic Nerve Involvement: The phrenic nerve, responsible for diaphragmatic function, arises from the C3, C4, and C5 nerve roots. Conditions affecting the apex of the lung can potentially irritate this nerve, leading to referred pain in the shoulder, particularly on the top of the shoulder or tip of the shoulder blade.

Inflammatory Responses: Some lung diseases can cause local inflammation, which may, in turn, affect nearby nerve pathways, leading to symptoms in the shoulder or arm.

Different Types of Lung Cancer and Their Link to Shoulder Pain

Pancoast Tumors (Superior Sulcus Tumors)

Pancoast Tumors (Superior Sulcus Tumors

Definition and Location: Pancoast tumors are a rare form of non-small cell lung cancer (NSCLC) that arise in the apex (top) of the lung, specifically in the superior pulmonary sulcus. Their unique location distinguishes them from other lung cancers [4].

How They Invade Local Structures:

  • These tumors have a propensity to invade nearby tissues, such as the chest wall, vertebrae, nerves, and vessels, especially the brachial plexus. This local invasion is often the cause of shoulder pain, often radiating down the arm, commonly termed as Pancoast syndrome [5].
  • Pancoast tumor or any other lung malignancy that extends to the apical region of the lung can impinge upon or invade the lower part of the brachial plexus, leading to shoulder pain. The patient may present with pain radiating down the arm, muscle weakness, and Horner’s syndrome – a combination of symptoms including drooping eyelids, pupil constriction, and absence of sweating on one side of the face [3].

Lung Adenocarcinoma

Lung Adenocarcinoma

Originates in the Peripheral Lung Tissues: Lung adenocarcinoma typically initiates from the outer parts of the lungs and is currently the most common subtype of lung cancer [6].

Leads to Pleural Involvement and Referred Shoulder Pain: As it grows, the tumor may involve the pleura, leading to pleuritic pain. Given the close anatomical relation, this pain can be referred to the shoulder.

Squamous Cell Carcinoma

Growth and Potential to Impinge on Surrounding Structures: This type of NSCLC has a tendency to grow in the central cavities in the lung, near the bronchi [7].

Centrally Located; Potential for Referred Shoulder Pain: Its central location means it can invade or compress surrounding structures. If there’s any involvement of nerve pathways or inflammatory response, it can potentially cause referred shoulder pain.

Large Cell Carcinoma

Rapid Growth and Varied Origins: Large cell carcinoma is named for the large, rounded cells seen under the microscope. It grows and spreads quickly, originating in any part of the lung [Reference: Cancer.org].

Potential Symptoms, Including Shoulder Pain: Depending on the location of the tumor and the structures it affects, shoulder pain can manifest as a symptom.

Small Cell Lung Cancer (SCLC)

Aggressiveness and Rapid Growth: SCLC is notorious for its rapid growth rate and its propensity to spread early primarily associated with smoking [8].

Causes Shoulder Pain Through Local Invasion or Bone Metastasis: Due to its aggressive nature, SCLC can cause shoulder pain either through direct invasion of structures near the top of the lung or through metastasis to bones of the shoulder girdle or spine.

Mesothelioma

Mesothelioma

A Cancer of the Pleura: Mesothelioma originates in the mesothelial cells of the pleura, the thin lining surrounding the lungs [9].

Causes Referred Shoulder Pain Due to Pleural Irritation or Invasion: As mesothelioma involves the pleura, it leads to pleuritic inflammation and pain, which can be referred to the shoulder, especially if the tumor is on the upper part of the pleura.

Metastasis from Other Cancers

How Cancers from Other Parts Metastasize to the Lungs: The lung is a common site for metastasis from cancers in other parts of the body, like breast, colon, or prostate cancer [10].

Symptoms Similar to Primary Lung Cancers, Including Shoulder Pain: Metastatic tumors in the lungs can produce symptoms similar to primary lung tumors. If these metastases are located at the top of the lung or invade the pleura, shoulder pain can arise.

Other Indirect Causes

While direct tumor invasion or proximity to the shoulder region can result in shoulder pain, there are indirect causes related to lung cancer treatments that may also lead to discomfort in this area.

Lung Surgery or Treatments Causing Musculoskeletal Pain in the Shoulder

Surgical treatments for lung cancer, such as lobectomy or pneumonectomy, can involve significant tissue disruption. Post-operative pain in the shoulder can result from surgical manipulation, positioning during surgery, or tissue healing [11].

Post-Surgical Pain: After lung surgery, such as a lobectomy or pneumonectomy, patients may experience shoulder pain. This can arise from the surgical approach, especially if the incision is made on the side or back of the chest wall, potentially affecting muscles and soft tissues around the shoulder. The pain could be due to direct surgical trauma or from maintaining a particular position during surgery.

Pleural Procedures: Any intervention involving the pleura, such as thoracentesis or pleurodesis, can lead to referred pain to the shoulder, given the close anatomical relationship.

Physical Immobility: Post-surgery, patients might be less mobile, leading to stiffness in the shoulder joint and subsequently pain.

Radiation Therapy Effects

While radiation therapy targets cancerous cells, it can also impact healthy surrounding tissue. After radiation therapy to the chest, a condition known as radiation pneumonitis, an inflammation of the lungs, may develop, causing symptoms such as shoulder and chest pain [12].

Radiation-Induced Dermatitis: Radiation therapy can cause skin changes in the irradiated area, ranging from mild redness to blistering. If the radiation field is close to the shoulder, the skin around this area can become inflamed and painful.

Radiation Fibrosis: Over time, radiation can lead to fibrotic changes in the underlying tissues, which can reduce the flexibility and mobility of the shoulder.

Brachial Plexopathy: Rarely, radiation can damage the brachial plexus, leading to pain, weakness, and sensory changes in the shoulder and arm.

Complications from Chemotherapy

Certain chemotherapy drugs can cause peripheral neuropathy, a set of symptoms caused by damage to nerves that control the sensations and movements of our arms and legs. This may manifest as pain, numbness, or tingling in the shoulder. Furthermore, some patients may develop drug-induced pneumonitis, which could also be associated with shoulder pain [13].

Peripheral Neuropathy: Some chemotherapeutic agents are neurotoxic and can cause peripheral neuropathy, a condition where the peripheral nerves are damaged. This can lead to pain, tingling, or numbness in the extremities, including the shoulder region.

Myalgia and Arthralgia: Some chemotherapy drugs can cause muscle pain (myalgia) and joint pain (arthralgia). The shoulder, being a major joint with surrounding muscles, can be affected.

Fluid Retention: Certain chemotherapy agents can lead to fluid retention in the body. Swelling or edema around the shoulder joint can cause pain and reduced mobility.

Importance of Early Diagnosis

The prognosis and management of lung cancer, like many other cancers, significantly depend on the stage at which it is detected. Early recognition can lead to timely investigations and potentially an earlier stage of diagnosis, which often correlates with better treatment outcomes [14].

Recognizing Shoulder Pain as a Potential Sign

Unexpected Symptom: While shoulder pain is a common complaint and can arise from various causes, recognizing it as a potential symptom of lung cancer, especially in the absence of trauma or musculoskeletal reasons, is crucial. This is particularly true for patients who are at high risk due to factors such as smoking, exposure to carcinogens, or a family history of lung cancer.

Pancoast Syndrome: As mentioned earlier, Pancoast tumors located at the lung’s apex can manifest with shoulder pain. Early recognition of this association can lead to timely interventions and better prognosis.

Mention of Other Symptoms of Lung Cancer for Holistic Awareness

While shoulder pain can be a notable sign, it’s essential to understand and recognize other symptoms associated with lung cancer. These include:

Persistent Cough: A continuous cough that doesn’t resolve or worsens over time can be indicative.

Hemoptysis: Coughing up blood or bloody sputum is a significant symptom requiring immediate attention.

Shortness of Breath: Difficulty breathing can arise from tumor obstruction or pleural effusion.

Chest Pain: Discomfort or pain in the chest, especially when coughing, breathing, or laughing.

Hoarseness: Changes in voice or persistent hoarseness can indicate tumor involvement of the laryngeal nerves.

Unexplained Weight Loss and Fatigue: Sudden weight loss without dietary or activity changes and persistent fatigue can be systemic symptoms of cancer.

Recurring Infections: Frequent respiratory infections like bronchitis or pneumonia can arise due to obstruction by the tumor.

Apart from shoulder pain, symptoms like persistent cough, hemoptysis (coughing up blood), shortness of breath, weight loss, and chest pain should also raise concerns. Recognizing the full spectrum of symptoms can expedite diagnosis and treatment [15].

Diagnosis and Treatment

Unveiling the presence and specifics of lung cancer often necessitates a multi-modality approach, combining imaging with invasive diagnostics, if necessary. Concurrently, managing symptoms, especially pain, forms a critical component of the care continuum. Here’s a more detailed look:

Diagnostic Methods for Lung Cancer

X-rays: A basic chest X-ray can provide an initial view of tumors in the lungs, although it might not detect smaller cancers or tumors embedded deeper in the lung tissue. Nevertheless, many lung cancers are found by routine chest X-ray [15].

CT Scans: A computed tomography (CT) scan provides a more detailed, cross-sectional view of the lung and can detect smaller lesions or nodules that X-rays might miss. CT scans are also essential for staging lung cancer by assessing the size, location, and extent of the disease. They are more sensitive than standard chest X-rays in identifying lung tumors [16].

MRI: Magnetic Resonance Imaging (MRI) is particularly helpful in evaluating the extent of tumor invasion into nearby tissues or the chest wall, including the brachial plexus. MRI can offer superior soft tissue contrast compared to CT scans. Magnetic Resonance Imaging might be used for staging lung cancer or understanding its spread, especially to the brain or spinal cord [17].

Biopsy: If imaging suggests a lung tumor, a biopsy is necessary to confirm the diagnosis. This involves taking a sample of the tumor tissue, which can be done through bronchoscopy, needle biopsy, or surgical biopsy, and examining it under a microscope.

Other Tests: Based on initial findings, further tests like PET scans might be used to check for metastasis or to get a better understanding of the tumor’s activity.

Role of Pain Management in Improving Patient’s Quality of Life

Pain management, whether pharmacological or through other therapies, is a critical aspect of comprehensive cancer care. Managing pain effectively can greatly improve the patient’s ability to function, maintain independence, sleep better, and enjoy personal interactions, thereby elevating their overall quality of life [18].

Chronic Pain: Many lung cancer patients experience chronic pain, be it from the tumor itself, metastatic sites, or treatment side-effects. Effective pain management can dramatically enhance the patient’s quality of life.

Multimodal Approach: Pain management often involves a combination of medications, physical therapy, and sometimes interventional procedures. Opioids, NSAIDs, nerve pain medications, and others can be tailored to the patient’s needs.

Alternative Therapies: Techniques like acupuncture, massage, and meditation can be supportive in managing pain and the stress associated with cancer.

Treatment Options for Lung Cancer

Depending on the type, stage, and location of the lung cancer, as well as the patient’s overall health, treatment options may include surgery, chemotherapy, radiation therapy, targeted therapy, immunotherapy, or a combination of these treatments [19].

Surgery: In cases where the tumor is localized and hasn’t spread, surgical removal, like lobectomy or pneumonectomy, might be recommended.

Radiation Therapy: This utilizes high doses of radiation to kill cancer cells or keep them from growing. It can be used as the primary treatment or post-surgery to kill any remaining cancer cells.

Chemotherapy: This systemic treatment uses drugs to kill cancer cells or stop their division. It can be administered orally or intravenously.

Targeted Therapy: Advances in understanding the genetics of tumors have led to the development of drugs that specifically target cancer cells based on their mutations. These drugs can block tumor growth and spread.

Immunotherapy: This is a newer approach that boosts the body’s natural defenses to fight cancer. It uses substances made in a lab or by the body to improve or restore immune system function.

Palliative Care: Beyond aggressive treatments, the focus for some patients might be on relieving symptoms and improving quality of life without necessarily targeting the cancer. This care is vital for advanced-stage patients.

Conclusion

Lung cancer, a leading cause of cancer deaths globally, often remains insidious in its early stages, manifesting through subtle and sometimes unexpected symptoms. The association between shoulder pain and lung cancer, as highlighted in this discussion, serves as a testament to the body’s intricate network and the ways in which distant organs can be affected. Recognizing these early signs, such as shoulder pain, is paramount for early diagnosis and intervention.

For readers, it’s essential to remember that while shoulder pain is common and often arises from benign causes, any persistent or unusual pain, especially when accompanied by other systemic symptoms, should never be overlooked. Seeking timely medical advice could mean the difference between early detection and late-stage discovery. Always prioritize your health, listen to your body’s signals, and remain proactive in seeking care. Your health is invaluable, and early action can pave the way for better outcomes.

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