Leg pain is common in cancer patients. But it can be hard to understand the cause and to offer a solution. Part of it is because there are several causes for cancer leg pain. So telling them apart can be a challenge. Still, some causes of pain are urgent. For instance, it is important not to miss a blood clot in a leg vein. Other times, pain can be a sign of cancer progression. For instance a metastases or enlarged lymph node might be pressing on a nerve.
Blood Clots
Blood clots are common in many types of cancer. There are several explanations for this. Some of the reasons are tied to molecules that the cancer secretes. Other times, the blood clots are actually a result of the cancer treatment.
A blood clot in a leg vein is called a deep vein thrombosis. Cancer patients have a higher likelihood for developing these blood clots than people without cancer. Also, once a clot develops, there is a higher chance that it will be extensive.
The symptoms of blood clots in the legs include leg swelling and leg pain. Sadly, sometimes the clot is so extensive that it will even jeopardize the artery flow to the leg. When this happens, we used the term “phlegmasia”. So, if a cancer patient develops sudden leg swelling and sudden pain, you must consider a blood clot as the cause.
The diagnosis of blood clots in cancer patients is similar to non-cancer patients. The most common test to use is an ultrasound. The advantages of ultrasound include safety, no pain, no radiation and no need for contrast.
Once we know there is a clot, the first treatment is with blood thinners. In the past, the main treatment were injections of a medication called low molecular weight heparin. But more recently, medications called DOAC have emerged as appropriate alternatives. Examples of these medications are rivaroxaban (Xarelto) and apixaban (Eliquis). Only patients with more advanced forms of clots will need procedures.
Cancer Leg Pain from Nerve Compression
Nerve compression can be very painful. In cancer patients, the cancer itself, or a metastases or an enlarged lymph node might compress a nerve. Certain cancer types, such as prostate cancer, tend to metastasize to the spine. If the metastases compresses the nerve roots coming out of the spine, this will cause pain in the leg. For this reason, if a cancer patient develops what looks like sciatica leg pain, you should think of nerve compression as well.
Cancer leg pain from nerve compression is sometimes worse at night. This has to do with position. When we lay in bed, the position of our spine changes. Sometimes that will make the compression worse. So new onset night leg pain in a cancer patient should raise the suspicion of nerve compression.
If you developed new-onset leg pain and you suspect that the cause is nerve compression, the next step is imaging. The type of imaging to use depends on the location of your pain. The two most common tests for cancer leg pain will be a CAT scan or an MRI. The purpose of these tests will be to look for compression of the nerve and to identify what is causing the compression.
Treatment of nerve compression usually means to treat the cancer. But, there are cases where the pain is severe or when there more neurological symptoms. For instance cauda equina syndrome, drop foot or incontinence. These other symptoms mean that the compression went beyond the pain fibers and other nerve components are involved. In these cases, we sometimes need more aggressive measures. Examples of options include emergency irradiation and surgery. The goal will be to shrink or remove the mass that is causing the compression.
Medication Side-Effects
Some cancer medicines can cause leg pain. Perhaps the most famous are medications that are used in multiple myeloma. Multiple myeloma patients often receive medications such as thalidomide and lenalidomide. Both these medicines cause neuropathy leg pain. The degree of neuropathy can be quite severe after using these medicines for a period of time and is often not reversible.
As I wrote in the previous section, some cancer medications can cause blood clots. Thalidomide, that I just mentioned as a cause for neuropathy, also causes blood clots.
If any of these side-effects happens in the context of cancer treatment, you will need to discuss your options with your oncologist. On the one hand, you may need the medication despite the side-effects. But sometimes there are alternatives. In these cases, limiting the side-effect by making a switch can make sense.
Other Types of Cancer Leg Pain
Cancer can cause pain in other ways. For instance, bone pain if the cancer spreads into bones. Bone pain is also a side-effect of some medications. For instance growth factors. While the intent is to stimulate the bone marrow to get more cells to grow, pain is also common.
Remember that many cancer treatments can cause pain. For instance, surgery or various tests. Unfortunately, cancer patients often need testing, and pain is one of the unwanted results. In this context, I should mention phantom pain. Phantom pain is a pain that is felt in a limb that is no longer there. Sadly, some cancer patients require amputation. For instance, after Ewing’s sarcoma. Cancer leg pain after the amputation might be phantom pain. Some have noted that increased phantom limb pain can be a sign of cancer recurrence or spread.
Another way cancer treatments can cause pain is through electrolyte imbalances. Sometimes, the reason is obvious. For instance, vomiting can change the blood pH and electrolyte composition. Other times, you need to really understand how the medication works to understand the problem. For instance, some medication side-effects include losing electrolytes in the urine. All these can result in muscle cramps. For this reason, cancer patients should not ignore muscle cramps. They should report them to their oncologists.
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