Assessment of Cancer Pain: Beyond the Basics

Robin L. Fainsinger, M.D., Associate Professor, Division of Palliative Medicine, Department of Oncology, University of Alberta, Edmonton, Alberta, Canada

Introduction

Pain presents in a variety of settings and situations, and can be categorized into acute pain, chronic non-malignant pain, and cancer pain. This brief review will focus on some of the complexities of cancer pain assessment and management. It is important to remember that regardless of a clinician's textbook understanding of pharmacological and non-pharmacological pain management, this information is of little value if the assessment is inaccurate in understanding the physiological and non-physiological underpinnings of the patient's pain syndrome. The basic approach to the international effort to improve pain management, has been to propose that better pharmacological management and increased use of opioids will provide effective analgesia in 70 to 95% of patients.¹ The "three step analgesic ladder" has been promoted by the World Health Organization in its guidelines "Cancer Pain Relief" as a method for health care providers to improve cancer pain management.² However although there is evidence that global consumption of opioids has increased, a basic approach to pharmacological management of cancer pain has still left a significant number of patients with intractable pain problems.³ In addition, in recent years there have been many reports of higher dose opioids resulting in side effects such as myoclonus, hallucinations, agitated delirium and seizures. ⁴ The failure of adequate pain assessment and recognition of the possible multidimensional aspects of a pain syndrome, can easily result in inappropriate application of the three step analgesic ladder and failure to provide adequate pain management.

Assessment

An approach to pain assessment can start with the following three questions: -

1. What is causing the pain?
2. How bad is the pain?
3. What may complicate pain management (poor prognostic factors)?

The first two points are the basics of pain assessment. It is important to clarify whether the pain is caused by the major presenting illness (e.g. cancer), indirectly related (e.g. increasing abdominal pain due to opioid induced constipation), caused by a treatment side-effect, or completely unrelated to the main presenting disease.

It is also important to differentiate nociceptive and neuropathic pain.⁵ Nociceptive pain includes somatic and visceral pain and is caused by the activation of normal nerve endings. Neuropathic pain is caused by injury to the nerve tissue and can be from peripheral nerve injury, damage to the autonomic nervous system, the central nervous system, or any combination of these different mechanisms. The main issue in differentiating neuropathic from nociceptive pain is to determine appropriate pharmacological management. Although there has been controversy with regard to the opioid responsiveness of neuropathic pain syndromes, there is now sufficient clinical and research experience to conclude that most neuropathic pains are opioid responsive, but may require higher doses and/or a different adjuvant analgesic regime. ^5,6

With regard to the severity of pain it is often recommended that a useful clinical approach is to use either a visual analogue scale, a numerical scale, or a number of other pain assessment tools described in the literature. ⁶ However it is important to remember that this simple approach to asking patients to assess their pain is ultimately a uni-dimensional not a multidimensional assessment. The complexity of a cancer patient's pain and suffering is well described by the following:

"It was true, as the doctor said that Ivan Ilych's physical sufferings were terrible, but worse than the physical sufferings were his mental sufferings, which were his chief torture."
"The Death of Ivan Ilych" by Tolstoy.

"It has been recognized, from a wide array of studies in many countries, that chronic pain has many psychological, sociological and cultural components." ⁷

"Ron Melzack taught us many things, but that which has most clearly guided our research is that pain is not simply the result of a bodily insult, but more the result of the interaction among the physical, psychological and cognitive states of the person in pain." ⁸

Some patients may be accurate in describing their pain severity from a physiological perspective alone. However some patients stating that their pain is 8/10 might mean: - "My back hurts a bit but I feel absolutely awful about my circumstances. I cannot cope with anything. Are you smart enough to hear my message?"

Beyond the Basics

We now live in a time where patients and families often read or hear in the media that physicians have sufficient pharmacological options to provide pain relief if they would only use opioids in sufficiently escalating doses. However as has been previously described ⁹, the wide diversity of opioid doses described in cancer patients has been reported using methods that do not allow us to explain the possible circumstances for this wide variability, and potential exposure to increasing opioid toxicity. A staging system for cancer pain has been proposed ^{10, 11} as a useful clinical and research tool that would include appropriate assessment of poorer prognostic factors for pain control. These factors include the pain mechanism, presence of severe incidental pain, complexity of pain management regime, cognitive impairment, psychosocial distress resulting in somatization, analgesic tolerance, and history of substance abuse suggesting poorer coping mechanisms. These potential complicating factors are best illustrated by the following alternative patient situations: - A 70 year old man with lung cancer and bone metastases presents with pain localized to the midback. He is comfortable, oriented and alert. He takes morphine 5 mg every four hours and is very comfortable. He has a longstanding stable marriage and home life, with no psychiatric history or history of addictive behavior; OR a 70 year old man with lung cancer and bone metastases presents with burning, stabbing pain down the right leg with a marked increase in pain if this area is touched. He is reasonable comfortable at rest, but any movement results in excruciating pain. He has poor attention and a fluctuating level of alertness. His morphine dose has increased from 5 mg every four hours to 200 mg every four hours over the last two weeks. He is also taking celecoxib, decadron, sertraline, and gabapentin. He has never been married and has a number of failed relationships, lives on his own, and has a history of depression and suicide attempts. He has continued to consume large amounts of alcohol and reports often requiring a drink first thing in the morning.

In considering the multidimensional aspects of these two examples, it is helpful to consider how these two patients pain syndromes may be produced, perceived, and expressed. ^{12, 13, 14} Production of pain occurs at the site of injury, and cannot be measured directly in these patients. The perception of pain occurs at the level of the central nervous system/brain, and cannot be measured in clinical settings. We ask patients to express their pain as the main target for assessment and management. However assuming in the above example that the two patients have a similar injury, they may even have similar levels of perception, but certainly we may anticipate that these two patient's coping mechanisms may result in a different intensity of expression. Certainly for the latter patient this requires a multi-dimensional assessment to consider the total suffering that may be included in an 8/10 description of pain.

Neuropathic pain has been discussed previously, and an extensive discussion of the alternative pharmacological management of neuropathic pain can be found elsewhere. ⁶ However the presence of a neuropathic pain syndrome has been well described as a potentially more complex and problematic pain syndrome. ^{15, 16, 17}

Incidental pain is important although the patient may be relatively comfortable at rest. The increased analgesic requirements for relatively brief movements may place the patient at risk for increased side effects during the rest of the day when this medication level is not required. Cancer related incident pain has been described as a prevalent and heterogeneous phenomenon, that may be a marker for more severe pain syndromes and be associated with both pain-related functional impairment and psychological distress. ¹⁸

Complicated analgesic regimes and a history of sequential opioid and adjuvant analgesic trials without success certainly presents a treatment dilemma. However a careful reassessment of the clinical situation will often reveal an underlying poor prognostic pain management factor that has gone unrecognized, resulting in an over reliance on pharmacological approach.

The need to recognize, adequately investigate and manage cognitive impairments in cancer patients has received increasing recognition. ^{19, 20} Cognitively impaired patients have increased difficulty in providing an accurate pain history, and are certainly more at risk of increasing confusion and agitation with both opioid and adjuvant analgesic management. Increasing agitated behavior may often be misdiagnosed as increasing pain, resulting in escalating pharmacological management and a hopeless vicious circle. The need to include assessments of cognition and consider possible reversible factors such as medications, metabolic problems, dehydration, infections and hypoxia has been emphasized. For some hospice and palliative care programs, this has required recognition that dehydration in terminally ill cancer patients may not be a benign phenomenon. ²¹ It has increasingly been recognized that the dehydration and resulting renal impairment in terminally ill patients not provided with sufficient parenteral hydration, will inevitably result in accumulation of opioids and opioid metabolites. Some patients may then go on to develop opioid induced side effects such as myoclonus, agitated delirium and even seizures, that may be misinterpreted as increasing pain resulting in increasing opioid doses.

Previous discussion has already described the psychosocial distress and somatization that may complicate the expression of pain in cancer patients. Although it is certainly wise to give patients the benefit of the doubt in prescribing adequate amounts of opioids, there may be elements of the history and physical findings that alert us to unrecognized psychosocial/ somatization issues. If we attempt to manage these problems with a pharmacological approach alone we will inevitably fail. Skilled intervention from a comprehensive interdisciplinary psychosocial support team can be invaluable in ensuring a more successful management outcome. ^{12, 13, 14}

There is good evidence that opioid doses do not usually require escalation in the absence of progressive injury from the underlying cancer. ¹⁷ However there is a small subset of patients for whom true opioid analgesic tolerance results in a poor response to escalating doses and may be associated with increasingly difficult side effects. ^{22, 23} These patients can often be managed by changing the opioid or the route of opioid administration.

Despite a past history of alcohol or other drug abuse, the literature evidence would suggest that these patients should still be prescribed opioids. Preexisting opioid tolerance may sometimes require higher opioid doses, but can still be expected to achieve good pain management. ²⁴ However it is important to recognize that an inability to cope with the stress of life prior to developing an advanced incurable illness, and a tendency to depend on cognitively impairing substances in order to assist coping mechanisms, may be a risk factor for replacing or supplementing previous addictions by the use of increasing opioid doses to achieve the same obtunding effect.

Conclusion

Developing expertise and confidence in the management of pain in cancer patients requires an understanding of the basic approach to assessment, and a grasp of the WHO "three step analgesic ladder". However increasing experience and exposure to the complexity of a wide variety of patients and cancer pain syndromes will inevitably result in interaction with the 5 to 30% of patients who do not respond well to a basic approach. Moving beyond the basics of pain assessment and management requires an increasing appreciation of the possible multidimensional aspects of a patient's pain experience.

References

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2. World Health Organization. Cancer Pain Relief. Geneva, Switzerland: World Health Organization; 1986.
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16. Sykes J, Johnson R, Hanks GW. Difficult pain problems. BMJ 1997; 315:867-869.
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18. Portenoy RK, Payne D, Jacobsen P. Breakthrough pain: Characteristics and impact in patients with cancer pain. Pain 1999; 91:129-134.
19. Fainsinger RL, Tapper M, Bruera E. A perspective on the management of delirium in the terminally ill. J of Palliative Care 1993; 9(3):4-8.
20. Lawlor PG, Fainsinger RL, Bruera ED. Delirium at the end of life. Critical issues in clinical practice and research. JAMA 2000; 284(19):2427-2429.
21. Fainsinger RL, Bruera E. When to treat dehydration in a terminally ill patient? Supportive Care Cancer 1997; 5:205-211.
22. McQuay H. Opioids in pain management. Lancet 1999; 353:2229-2232.
23. Fainsinger RL, Bruera E. Case report: Is this opioid analgesic tolerance. J of Pain & Sympt Manage 1995; 10(7):573-577.
24. Kaplan R, Slywka J, Slagle S, et al. A titrated morphine analgesic regime comparing substance users and non-users with AIDS - related pain. J of Pain & Sympt Manage 2000; 19:265-273.

Jacksonville Medicine / May, 2001

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