Cancer Pain (PDQ®)–Health Professional Version
Pain Classification
Total Pain
The concept of total pain captures its multidimensional nature by explicitly including the physical, psychological, social, and spiritual components of pain.[1-4] The immediate implications for the clinician are severalfold:
- A complete assessment of pain requires screening for psychological distress, social disruption, and existential crises, to treat the pain effectively and to anticipate barriers to pain relief.
- Patients’ descriptions of pain that seem out of proportion to the known pathology may reflect other syndromes such as depression and existential distress.[5]
- Patients suffering from pain often require multidimensional interventions from supportive services such as palliative care, chaplaincy, or psychotherapy.[6]
- The concept of total pain does not suggest that pain is solely caused by psychological or existential distress, but that psychological and spiritual components can exacerbate or ameliorate the experience of pain. If the clinician suspects somatization, then referral for psychiatric or psychological evaluation is indicated.
Pain Mechanisms
Pain is classified on the basis of the underlying pathophysiologic mechanisms, the duration, or the description of recognizable syndromes associated with pain.[7] The three mechanisms underlying the pathophysiology of pain are nociceptive, neuropathic, and psychogenic.
Nociceptive pain, which may be either somatic or visceral in nature, originates with a chemical, mechanical, or thermal injury to tissue that stimulates pain receptors that transmit a signal to the central nervous system (CNS), causing the perception of pain. Pain receptors are found in somatic (e.g., cutaneous, bone) and visceral tissues. The amount of visceral sensory innervation and the diffusion of visceral pain signals within the brain explain the difficulty experienced by patients in describing or localizing visceral pain compared with somatic pain. A specific type of visceral pain is referred pain, which is explained by the commingling of nerve fibers from somatic and visceral nociceptors at the level of the spinal cord. Patients mistakenly interpret the pain as originating from the innervated somatic tissue. Visceral pain may be accompanied by autonomic signs such as sweating, pallor, or bradycardia. Somatic pain is more easily localized.
Neuropathic pain is pain caused by damage to the peripheral nervous system or the CNS (spinal cord or brain). Causes of neuropathic pain of particular relevance to cancer include chemotherapy (e.g., vinca alkaloids), infiltration of the nerve roots by tumor, or damage to nerve roots (radiculopathy) or groups of nerve roots (plexopathy) due to tumor masses or treatment complications (e.g., radiation plexopathy).[8] The pain may be evoked by stimuli or spontaneous. Patients who experience pain from nonnoxious stimuli are classified as having allodynia. Hyperalgesia connotes increased sensations of pain out of proportion to what is usually experienced.
Emotional distress may also contribute to the pain experience. Most patients with cancer and pain do not have somatic symptom disorder. However, if pain complaints appear to be disproportionate to the underlying pain stimulus, it is important to evaluate for psychological and existential distress contributing to the pain complaint, chemical coping, and substance abuse.
Acute and Chronic Cancer Pain
Pain is often classified as either acute or chronic or by how it varies over time with terms such as breakthrough, persistent, or incidental. Acute pain is typically induced by tissue injury, begins suddenly with the injury, and diminishes over time with tissue healing. There is no definite length but, in general, acute pain resolves within 3 to 6 months.[9] The treatment of acute pain focuses on blocking nociceptive pathways while the tissue heals.
Chronic pain typically persists even after the injury has healed, although patients with chronic joint disease, for example, may have ongoing tissue damage and therefore experience chronic pain. Pain becomes chronic when it continues for more than 1 month after the healing of precipitating lesions; persists or becomes recurrent over months; or results from lesions unlikely to regress or heal.[9] The transition from acute to chronic pain may be understood as a series of relatively discrete changes in the CNS,[9] but there are also clearly behavioral confounders in the genesis of chronic pain. Chronic pain involves the activation of secondary mechanisms such as the sensitization of second-order neurons by upregulation of N-methyl-D-aspartic acid channels and alteration in microglia cytoarchitecture. Chronic pain, with its multiple factors for perpetuation, often benefits from a multidisciplinary approach to treatment.
Breakthrough Pain
In caring for patients with pain, breakthrough pain is distinguished from background pain.[10,11] Breakthrough pain is a transitory increase or flare of pain in the setting of relatively well-controlled acute or chronic pain.[12] Incident pain is a type of breakthrough pain related to certain often-defined activities or factors such as movement increasing vertebral body pain from metastatic disease. It is often difficult to treat such pain effectively because of its episodic nature.[13] In one study, 75% of patients experienced breakthrough pain; 30% of this pain was incidental, 26% was nonincidental, 16% was caused by end-of-dose failure, and the rest had mixed etiologies.[14]
References
- Richmond C: Dame Cicely Saunders. Br Med J 331 (7510): 238, 2005. Also available online. Last accessed September 10, 2018.
- Mehta A, Chan LS: Understanding of the concept of “total pain”: a prerequisite for pain control. J Hosp Palliat Nurs 10 (1): 26-32, 2008.
- Syrjala KL, Jensen MP, Mendoza ME, et al.: Psychological and behavioral approaches to cancer pain management. J Clin Oncol 32 (16): 1703-11, 2014. [PUBMED Abstract]
- Merskey H, Bogduk N, eds.: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 2nd ed. Seattle, Wash: IASP Press, 1994. Also available online. Last accessed September 10, 2018.
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- Wachholtz A, Makowski S: Spiritual dimensions of pain and suffering. In: Moore RJ, ed.: Handbook of Pain and Palliative Care: Biobehavioral Approaches for the Life Course. New York, NY: Springer, 2013, pp 697-713.
- Chang VT, Janjan N, Jain S, et al.: Update in cancer pain syndromes. J Palliat Med 9 (6): 1414-34, 2006. [PUBMED Abstract]
- Dworkin RH, Backonja M, Rowbotham MC, et al.: Advances in neuropathic pain: diagnosis, mechanisms, and treatment recommendations. Arch Neurol 60 (11): 1524-34, 2003. [PUBMED Abstract]
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Pain Assessment
Patient-Reported Outcomes
Effective pain treatment begins with screening at every visit and a thorough assessment if pain is present. Patient self-report is the standard of care for evaluating pain.[1]
Many tools have been developed to quantify the intensity of pain. The most commonly used tools include the numerical rating scale (0–10: 0 = no pain, 10 = worst pain imaginable); the categorical scale (none, mild, moderate, severe); and the visual analog scale (0–100 mm: 0 mm = no pain, 100 mm = worst pain imaginable). Multidimensional pain assessment tools such as the McGill Pain Questionnaire, the Brief Pain Inventory,[2] and the PROMIS-PI (Patient-Reported Outcomes Measurement Information System—Pain Interference) [3] have been developed to evaluate pain and its interference with daily functions. Although these tools are important, they may be best applied in the research setting, given their complexity and significant time requirements.
Pain assessment tools have been developed for special populations such as children and those with cognitive impairment (refer to the Special Considerations section of this summary for more information).
Pain intensity may be assessed for different time frames, such as “now,” “last 24 hours,” or “last week.” In addition to the average pain intensity, the worst or lowest intensity may be assessed. Evaluation of pain intensity at each visit would allow clinicians to monitor for changes and treatment response. Pain intensity scales can also be used to develop a personalized pain goal.[4]
Clinician Assessment
Failure to assess pain adequately leads to undertreatment. Assessment involves both clinician observation and patient report. The goal of the initial pain assessment is to characterize the pathophysiology of the pain and to determine the intensity of the pain and its impact on the patient’s ability to function. It is important to recognize that psychosocial issues can either exacerbate or ameliorate the experience of pain.[5] These psychosocial issues cannot be easily treated through pharmacologic approaches; therefore, it is critical that clinicians include these in initial and subsequent examinations of patients with pain to ensure referrals to appropriate treatment resources. Furthermore, distinct cultural components may need to be incorporated into a multidimensional assessment of pain, including how culture influences the pain experience, pain communication, and provider response to pain expression.[6-9]
Identifying the etiology of pain is important to its management. Clinicians treating patients with cancer need to recognize the common cancer pain syndromes. (Refer to the Approach to Somatic Pain, Approach to Visceral Pain, and Approach to Neuropathic Pain sections of this summary for more information.)
Effective pain management requires close monitoring of patient response after treatment is initiated. In a review of 1,612 patients referred to an outpatient palliative care center, more than half of patients with moderate to severe pain did not show pain relief (a reduction in 2 out of 10 points or a 30% decrease on the pain scale) after the initial palliative care consultation.[10] In addition, one-third of patients with mild pain progressed to moderate to severe pain by the time of their first follow-up visit. The study also identified baseline pain intensity, fatigue, and Edmonton Symptom Assessment System symptom burden as factors predicting response.[10]
Ideally, comprehensive pain assessment includes a discussion about the patient’s goals and expectations for pain management. This conversation may lead to a fruitful discussion about balancing pain levels and other patient goals, such as mental alertness. Comprehensive pain assessment also includes pain history, pain intensity, quality of pain, and location of pain. For each pain location, the pattern of pain radiation is assessed. Also important is provider awareness of the patient’s current pain management treatment plan and how the patient has responded to treatment; this includes how adequately the current treatment plan addresses any breakthrough or episodic pain. A full assessment also reviews previously attempted pain therapies and reasons for discontinuation; other associated symptoms such as sleep difficulties, fatigue, depression, and anxiety; functional impairment; and any relevant laboratory data and diagnostic imaging. A focused physical examination includes clinical observation of pain behaviors, pain location, and functional limitations.
Psychosocial and existential factors that can affect pain are also assessed and appropriately treated. Depression and anxiety can have a large influence on the pain experience. Across many different types of pain, research has shown the importance of considering a patient’s sense of self-efficacy over their pain: low self-efficacy, or focus on solely pharmacologic solutions, is likely to increase the use of pain medication.[11,12] In addition, patients who repeatedly catastrophize pain (e.g., patient reports pain higher than 10 on a 10-point scale) are more likely to require higher doses than are patients who do not catastrophize. Catastrophizing is strongly associated with low self-efficacy and reliance on chemical coping strategies.[13-17] Furthermore, assessing the impact of pain on the individual’s life and associated factors that exacerbate or relieve pain can reveal how psychosocial issues are affecting the patient’s pain levels.
A pain assessment includes a review of any patient and family history of substance use and the extent of the patient’s chemical coping strategies before and since the cancer diagnosis. The extent of chemical coping strategies, including reliance on legal substances (e.g., nicotine, alcohol, and sleeping pills), may indicate a history of reliance on chemicals to alleviate distress. It can also provide the clinician with information about the patient’s nicotine use, which may affect how certain opioids may be differentially metabolized and the amount of opioids required to achieve pain control.[18] A remote history of substance abuse can still affect current pain levels and analgesic requirements. Remote substance use may have long-term implications for pain sensitivity, even if the patient has a history of prolonged abstinence from opioid use.[19] Together, personal and family substance use can inform a risk assessment for potential abuse of medications, potential analgesic requirements, and diversion of prescriptions.
Pain Prognostic Scores
A number of pain-related factors and patient-related factors predict response to pain treatment. Specifically, a high baseline pain intensity, neuropathic pain, and incident pain are often more difficult to manage.[20] Furthermore, several patient characteristics such as a personal or family history of illicit drug use, alcoholism ,[21,22] smoking,[23-25] somatization,[26] mental health issues such as depression or anxiety,[27] and cognitive dysfunction [28-30] are associated with higher pain expression, higher opioid doses, and longer time to achieve pain control.
On the basis of these predictive factors, several risk scores have been developed to assist clinicians in clinical practice, such as the Edmonton Classification System for Cancer Pain (ECS-CP) [20,31] and the Cancer Pain Prognostic Scale (CPPS).[32]
- The ECS-CP consists of (1) neuropathic pain, (2) incident pain, (3) psychological distress, (4) addiction, and (5) cognitive impairment. The presence of any of these factors indicates that pain may be more difficult to control. The ECS-CP has been validated in various cancer pain settings.[33]
- The CPPS includes four variables in a formula to determine the risk score, including worst pain severity (Brief Pain Inventory), Functional Assessment of Cancer Therapy - General (FACT-G) emotional well-being, initial morphine equivalent daily dose (≤60 mg/day; >60 mg/day), and mixed pain syndrome. The CPPS score ranges from 0 to 17, with a higher score indicating a higher possibility of pain relief.
Predictive factors can help to personalize cancer pain management. Especially for patients with a poor pain prognosis, clinicians may consider discussing realistic goals for alleviating pain, focusing on function and use of multimodality interventions. Repeated or frequent escalation of analgesic doses without improvement of pain may trigger clinicians to consider an alternative approach to pain.
Special Considerations
Self-report is accepted as the gold standard of pain assessment; however, for certain vulnerable populations, such as children, those with learning disabilities, and those who are cognitively impaired, self-report may not be feasible or reliable.
While adults and children older than 7 years can effectively utilize the numerical rating scale, young children and those with cognitive impairment may benefit from using a pictorial scale such as the Faces Pain Scale.[34] (Refer to the PDQ summary on Pediatric Supportive Care for more information.)
Cognitive impairment may impede a person’s ability to describe pain, recall pain events, or understand the tools used to assess pain, leading such patients to receive more or less analgesia.[35-37] The American Society for Pain Management Nursing has developed a position statement on pain assessment in the nonverbal patient that includes clinical recommendations.[38] Pain assessment can be evaluated via direct observation, family/caregiver report, and evaluation of response to pain relief interventions. For patients with advanced dementia, tools relying on professional caregiver assessment of pain through the observation of patient behaviors have been developed.[39-41] Although the validity and reliability of these tools have been questioned, the tools are often recommended for patients with advanced dementia who cannot report pain and, in combination with self-report by other cognitively impaired groups, as a means to enhance pain assessment and avoid undertreatment of pain.
Cognitive impairment extends beyond patients with a diagnosis of dementia, such as those with brain tumors and delirium, which are common complications of advanced cancer. In such patients, the Faces Pain Scale [42] and the Coloured Analogue Scale [43] as well as vertical instead of horizontal orientation of scales may be preferable to the numeric rating scales.[44]
Culture also plays a role in the patient experience of pain and the reporting of pain. For example, among some Asian cultures, patients tend not to report pain.[6] Complaining of pain may be perceived as a sign of weakness. Individuals may hide pain from family members to avoid burdening the family. For some patients, pain may have spiritual value, leading them to accept pain rather than dull the experience with medication.[45] Thus, understanding an individual patient’s spiritual and cultural background without making assumptions is important in approaching pain assessment.
In a cross-sectional study, the cancer pain experience of white patients was individual and independent, while that of ethnic minority patients was family oriented. Minority patients received support from their families during the cancer treatment, and they fought cancer for their families. The families were involved deeply in their decision making related to cancer treatment and pain management.[7]
References
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- Fainsinger RL, Fairchild A, Nekolaichuk C, et al.: Is pain intensity a predictor of the complexity of cancer pain management? J Clin Oncol 27 (4): 585-90, 2009. [PUBMED Abstract]
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