Bone pain is a specific cancer pain syndrome that also happens to be the most common cause of cancer pain. Cancer involvement of bone is also something that can be seen with numerous types of cancer. It is a type of somatic pain, which is “body-related” pain, as I mentioned in my Pain 101 post.

The more common bone sites for metastases include the spine, skull, humerus (upper arm), ribs, pelvis, and femur (hip bone).   The more common cancers that cause bony metastases include lung, breast, prostate, and multiple myeloma.   The incidence of bone involvement varies among these different cancers, but for example in lung cancer, up to 24% of patients have bony metastases.   Bone pain in cancer also occurs as a complication of certain treatments, such as avascular necrosis (bone death in the large hip or shoulder bones) due to steroid treatments or osteoradionecrosis (bone death after radiation, particularly in the jaw bone).  I will focus primarily on bone pain from metastases in this post.

Why do bone metastases cause pain?  While the mechanisms are not completely understood, it is thought that cancer metastases disrupt the normal balance of bone building and bone resorption (bone breakdown); this imbalance contributes to the pain.   The pain is usually constant and localized; it can sometimes “refer” or be felt in other adjacent locations.   Patients often describe bone pain as an ache, versus the shooting electrical qualities of neuropathic pain, and it often gets worse with certain activity.  Should the bone metastasis cause a fracture or damage a nerve, then the pain can become more complex and severe, with qualities of both somatic pain and neuropathic pain.

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Neuropathic pain is a common pain syndrome for patients with cancer. As I mentioned in my introductory pain post, neuropathic pain is one of the three main types of pain (somatic, visceral, and neuropathic).  It is nerve-related and is typically described as an electrical or burning sensation; it can occur both due to damaged peripheral nerves (outside of the spinal cord and the brain) or damage within the central nervous system (CNS, which includes the spinal cord and brain).   Because of associated nerve injury, some patients can develop decreased sensation or actual muscle weakness.  While there are certainly isolated instances of pure neuropathic pain, often neuropathic pain is part of a “mixed” syndrome in which a patient can have neuropathic pain in conjunction with the other types of pain as well.

Why does this pain develop when a nerve is damaged, even after the injury has occurred?   Nerves that are damaged can begin to have abnormal sensing—the pain fibers in the nerves can become more sensitive due to damage and can also trigger pain spontaneously.   In the spinal cord, the signals from pain can be amplified by nerve damage—this causes the pain response to be much higher than expected to minor stimuli (a bedsheet touching the feet or something cold hitting the skin).

In hearing about neuropathic pain, we often think of the hands and feet being affected and feeling paresthesias (pins and needles) there, but neuropathic pain can occur anywhere there are nerves.   In cancer, the mechanism of nerve injury can occur through three main ways:

1) direct pressing on the nerve by tumor

2) cancer treatments toxic to nerves

3) paraneoplastic syndromes where the cancer causes an abnormal reaction from the body’s autoimmune system against the nerves.  Paraneoplastic syndromes are much less common, so I won’t be discussing this.

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Opioids are a class of pain medications that are frequently used for cancer-related pain, and for good reason. They target the opioid receptors, which are found throughout our body and effect pain transmission in the nervous system, from our peripheral nerves all the way to the brain.  Of note, our bodies make natural opioids—you may have heard of endorphins or enkephalins, which act on these opioid receptors as well. Opioids can help with all three main types of cancer-related pain that I mentioned in my last post: somatic (body-related), visceral (organ-related), and neuropathic (nerve-related). Opioids are usually used by physicians if medications such as tylenol or NSAIDs (like ibuprofen) aren’t working.

Examples of opioids include morphine, hydrocodone, oxycodone, dilaudid (hydromorphone), or fentanyl.  There are several others, but those are the most common.  They come in many different forms (pill, liquids, intravenous or subcutaneous, transdermal) so that there are quite a few options that can be tailored based on patients’ individual characteristics.

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In reviewing posts from GRACE, it’s not surprising to see that pain is major issue for many patients with cancer. Pain is not unique to cancer, but for most patients with cancer, their pain is related to the cancer in some way. In cancer, the causes of pain not only include the disease itself, but also the treatments and procedures involved. There are particular types of pain and pain syndromes that are seen primarily in patients with cancer compared to other illnesses. Within oncology and pain management, cancer pain is so crucial for patient care that it has become essentially its own specialty in recent years. Dr. Janet Abrahm, an oncologist and cancer pain expert at the Dana Farber, has written one of the definitive texts on cancer pain management which is a major reference for this post.

Cancer-related pain can be categorized in several ways into what time course it follows. Patients who have acute cancer-related pain have pain that is expected to improve with cancer-directed therapy or, if it is a treatment-related complication, will resolve after treatment. Chronic cancer-related pain is not expected to resolve or its source cannot be eradicated. This chronic pain is very frustrating; similar to non-cancer patients with chronic pain, treatment focuses on therapies that can help patients function and improve their quality of life.

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