Importance of Assessing, Treating Pain in the Cancer Patient

CLEVELAND—A comprehensive evaluation of acute and chronic pain in the cancer patient is essential in order to choose the appropriate therapy, detect the progression of disease, and optimize quality of life, Donna S. Zhukovsky, MD, of the Harry R. Horvitz Center for Palliative Medicine at the Cleveland Clinic Foundation, said at a conference on palliative medicine sponsored by the Cleveland Clinic Foundation.

In addition to a medical history, such an evaluation must include the patient’s functional status, as well as social and psychological factors. Depression, anxiety, loss of financial autonomy, and changes in the patient’s role within the family and community can all affect the perception of pain. “Failure to address all contributing factors will not result in the treatment goal, which is to optimize the quality of life,” Dr. Zhukovsky said.

The importance of proper pain diagnosis and control was shown by a study of 276 consecutive pain service consultations conducted at Memorial Sloan-Kettering Cancer Center, Dr. Zhukovsky said. In 64% of patients, the evaluation identified a previously undiagnosed etiology for the pain.

There are two basic categories of cancer pain, nociceptive and neuropathic, Dr. Zhukovsky said. Nociceptive pain can be somatic or visceral. Somatic pain is well-localized and usually described as aching, throbbing, and gnawing. It is caused by the activation of nociceptors in skin and deep tissues, as, for example, when tumor invades soft tissue.

Visceral pain, by contrast, is poorly localized, she said. Patients describe deep aching, cramping, and pressure. It is caused when stretched, distended, or inflamed thoracic or abdominal viscera activate nociceptors. Referred pain is also visceral pain.

Neuropathic Pain

The other category of cancer pain, neuropathic pain, is described as burning, shooting, stabbing, or vice-like. Patients may say it feels like bugs crawling on their skin, and they may say they feel like they’re going crazy. Neuropathic pain is caused by injury to the peripheral or central nervous system, due to tumor infiltration, chemotherapy, or radiation. Neuropathic pain is an unfamiliar experience for most people.

Neuropathic pain is generally difficult to treat well, she said. It may be less opioid responsive than nociceptive pain. Adjuvant agents, like antidepressant drugs or anticonvulsants, play a main role in its treatment, Dr. Zhukovsky said.

Most cancer patients require several modalities of pain control. These include disease-specific therapy, drugs, physical therapy, and cognitive-behavioral therapy. For a small group of patients, invasive anesthetic and surgical techniques of pain control may be extremely beneficial, she said. Transcutaneous electrical nerve stimulation (TENS), a noninvasive technique of neuroaugmentation that involves a battery-powered generator applied to the skin, has proven useful for some patients.

Giving Pharmacologics

There are three classes of pharmacologics for treating pain: nonopioids (acetaminophen, aspirin, and other nonsteroidal anti-inflammatories), opioids, and adjuvant analgesics, Dr. Zhukovsky said. Pharmacologics should be administered following a few basic principles, she said.

First, believe the patient’s complaint of pain. The literature shows that physicians tend to underestimate the patient’s degree of pain, she said. Perform a complete evaluation.

When prescribing, start with one drug at a time and allow an adequate trial before deciding the drug is ineffective (see description of the WHO ladder below).

Choose the appropriate route of administration, she said. Although oral administration is preferred, it may not be feasible. Routes of drug administration include oral, rectal, sublingual, parenteral, spinal (epidural, intrathecal), trans-dermal, and transbuccal.

Provide regularly scheduled drug administration for chronic pain and supplemental or “rescue” doses for breakthrough pain.

Anticipate and treat side effects. When starting an around-the-clock opioid regimen, for instance, expect constipation and start a bowel regimen as well. Continuously assess pain control to note any changes.

Finally, remain readily available to the patient.

The WHO Ladder

When prescribing pain control, clinicians should follow the World Health Organization three-step analgesic ladder, which allows for the sequential use of progressively stronger analgesic agents, in combination with adjuvant therapies if indicated. “You can start on whatever step is needed,” she said.

In step 1, a nonopioid is used. If this does not relieve the pain, an opioid for mild to moderate pain should be added (step 2). If this combination strategy fails, an opioid for moderate to severe pain should be substituted, with nonopioid and adjuvant therapies continued if appropriate (step 3).

Only one drug from each of the groups should be used at the same time. If a step 2 opioid ceases to be effective for the patient, the clinician should prescribe a stronger agent rather than switch to an alternative step 2 drug.

Use of Opioids

The nonopioids, unlike opioids, all have a ceiling effect. After a certain point, if the dose is increased, no additional analgesia is obtained but side effects worsen. When combination drugs such as Percocet (oxycodone and acetaminophen) are used, the nonopioid component limits dose escalation.

Opioid dosages, on the other hand, can be increased as needed. Patients may ask if they are receiving a high dose, Dr. Zhukovsky said. Remind patients that “numbers don’t matter,” she said. “The right dose is the one that adequately controls pain.”

Some clinicians may be surprised to learn that parenteral infusion of opioids is quite feasible even with home care. Use a 25-gauge needle under the skin on the chest or belly, Dr. Zhukovsky said. There are some volume constraints with this mode of administration.

Rescue doses, used for breakthrough pain, may be needed up to four times a day even in patients with well-controlled pain, she noted.

Side effects of opioids include constipation, sedation, and altered mental status, nausea and vomiting, orthostatic hypotension, and dry mouth. Except for constipation, patients rapidly develop tolerance to these side effects. Preventing dry mouth may be “particularly problematic,” she said. Meticulous mouth care is important. Sucking on ice chips may also help.

Morphine is the standard used for comparison among different opioid analgesics. “However, it’s good to have a variety of opioids to handle patients with various side effects,” Dr. Zhukovsky said.

Codeine, which metabolizes to morphine, is more nauseating and constipating than morphine. Heroin, although available for medicinal use in the United Kingdom and Canada, is unavailable in the United States. Around-the-clock use of meperidine is contraindicated, since it leads to the accumulation of norme-peridine, a toxic metabolite.

Clinicians can use the phenomenon of cross-tolerance to better manage sedation and nausea and vomiting in patients receiving opioid therapy, she said. By alternating opioids, the patient receives the benefit of analgesia with fewer side effects. The alternate opioid should be given at half the equianalgesic dose, Dr. Zhukovsky said.

She noted that nausea and vomiting may also be helped by switching modes of administration or by administering an antiemetic. Opioid-related sedation can also be helped by opioid rotation or by administration of a stimulant such as methylphenidate, she added.