1. What are the most common causes of pain in patients with cancer?

Pain in patients with cancer may be due to tumor involvement of pain-sensitive structures, to complications of therapy, or to processes not directly related to the cancer. The most common cause of pain in cancer is bone metastases. This is a nociceptive pain syndrome. Having said that, cancer patients can suffer from those pain conditions that patients without cancer develop. Because of abnormal posture, muscle wasting, malnourishment, unsteadiness and immobility, to name but a few, cancer patients can develop mechanical problems that generate pain. Therefore, it is important that a diagnosis is made of the cause of the pain, defining whether it is cancer related or not and which pain-sensitive structure is irritated and causing pain.

2. Is it common for patients with cancer to have more than one painful site?

Yes. In a large study of patients with severe cancer pain, 25% reported pain in two or more sites. Another survey, not limited to severe pain, showed an even higher prevalence of multiple painful sites. Furthermore, multiple sites may have multiple etiologies. For example, a patient with lung cancer could conceivably have postthoracotomy pain from the original surgery, multiple bone metastases, and a painful peripheral neuropathy from chemotherapy.

3. Name some neuropathic pain syndromes commonly seen in patients with cancer

Tumor invasion of the brachial or lumbosacral plexus is common in patients with cancer. Chemotherapy-related neuritis, postherpetic neuralgia, phantom limb pain, and peripheral neuropathy also occur frequently.

4. How common is neuropathic pain in patients with cancer?

Pain that can be inferred to be due to neurological lesions accounts for approximately 40% of severe pain syndromes. Although the somatic nociceptive pain syndromes are most common overall, patients with neuropathic pain are more likely to be referred to a pain specialist, presumably because of the inherent difficulty in treating these syndromes.

5. Which factors predispose a patient to develop postherpetic neuralgia (PHN)?

Advancing age is the most important factor that predisposes a patient to develop postherpetic neuralgia (PHN). The incidence of PHN rises exponentially after age 70. It is also more common in cancer and immunosuppressed patients than it is in the normal population. PHN commonly occurs in irradiated parts of the body. The trigeminal nerve (ophthalmic division) may also be predisposed to PHN.

Unfortunately, none of these factors can be controlled. There is some evidence to suggest that the severity of the rash and pain during the acute outbreak may predispose to later pain, so early and aggressive treatment may cut down the incidence of PHN. Also, the administration of analgesic antidepressants during the acute outbreak has been shown to be helpful.

6. Are opioids known to increase the risk of acute herpes zoster eruptions? Are opioids known to increase the subsequent development of PHN in patients who get acute zoster eruptions?

Opioids are not known to increase the risk of acute zoster eruptions nor do they increase the risk of postherpetic neuralgia. In fact, good pain control during the acute phase may lessen later pain.

7. Describe the pain syndrome associated with metastases to the clivus

Pain associated with metastases to the clivus is characterized by a vertex headache and exacerbated by neck flexion. There may be associated abnormalities of the lower cranial nerves, most commonly dysphagia from involvement of the glossopharyngeal nerve (IX). Occasionally, there is weakness of the trapezius from involvement of the spinal accessory nerve (XI).

8. Which types of malignancies are least likely to be painful?

Leukemia malignancies are least likely to be painful. In general, solid tumors of viscera and metastatic, invasive, destructive, and nerve-compressing cancers are more painful than leukemias. Bone metastases are the most common cause of pain in patients with cancer.

9. Is phantom limb sensation common after amputation?

All amputees, including those with cancer-related amputations of limbs and some other parts (i.e., breast, penis, rectum, nose, ears), almost invariably experience phantom sensations the day after surgery. These sensations are not always painful and may not be reported spontaneously. A small proportion of these patients go on to experience phantom limb pain. The rest have sensations that may or may not subside.

10. What is meant by incident pain?

Incident pain is when a mass, metastatic lesion, or pathologic fracture causes pain on movement, such as repositioning, deep breathing, or ambulation. This can be a very difficult pain to control, and it may be necessary to immobilize the injured structure. Anesthesiologic or ablative procedures may be required if analgesics are not helpful. Also, medication can be given before the precipitating event on an as-needed basis (e.g., before radiation therapy or physical therapy). Incident pain can also be related to therapy: cannula insertion, venipuncture and physical therapy can all be associated with incident pain.

Breakthrough pain may occur at the end of a dosing interval. It is easier to overcome, simply by shortening the dosing interval or increasing the amount of each dose.

11. What is the postthoracotomy pain syndrome?

There are two types of postthoracotomy pain: (1) immediate postoperative pain, which clears in 3 months and is associated with sensory loss in the area of scar, and (2) postoperative pain that lasts longer than 3 months or recurs in the surgical area following resolution of the initial postoperative pain. When pain recurs after a pain-free interval, suspect tumor recurrence or infection. When these are not found, the pain is most likely neuropathic.

12. True or false: cancer patients with new onset of progressive headaches should undergo imaging studies, even if there are no objective findings on exam

True. Headache is the most common symptom in patients with brain metastasis, and it is the most common neurologic complication or symptom of systemic cancer and carcinomatous meningitis. Headaches may appear to be of the tension type, but tend to progress in duration and severity (see Chapter 14, Brain Tumor Headaches). Eventually, focal neurologic deficits develop in most patients.

13. What are the clinical differences between radiation injury to the brachial plexus and tumor involvement of the plexus?

A woman with breast cancer treated with mastectomy and radiation of the brachial plexus region may develop ipsilateral pain with arm and hand weakness (a brachial plexopathy) after her treatments. If the symptoms are referable to the lower brachial plexus (i.e., lower trunk), it is most likely due to tumor recurrence. Radiation is more likely to cause a panplexopathy (i.e., involvement of all three trunks of the brachial plexus).

Horner’s syndrome is more common in tumor involvement. Electrophysiologically, myokymia is more commonly seen with radiation injury than with direct tumor involvement.

14. Why do women treated with radical mastectomy have a numb area just distal to the axilla on the inner upper part of the arm?

Injury to the intercostobrachial nerve is common in mastectomy patients and results in numbness in this specific area (Fig. 26-1). In some patients, neuropathic pain develops in the same location.

Figure 26-1 Area of numbness of the intercostobrachial nerve in mastectomy patients.