Despite the vast resources spent on pain management, many patients with cancer continue to have severe, unrelieved pain.1,2 Cancer pain is associated with a variety of physical and emotional symptoms including disability, loss of sleep, and depression.3-7 Neuropathic pain is present in at least 25% to 40% of people with cancer pain and is thought to be more difficult to control than other types of cancer-related pain.8,9
Relationships between neuropathic pain and diminished physical and psychological well-being have been well documented in nononcology patients.10-14 Studies indicate that people with neuropathic pain experience a significant burden of illness. This includes poor general health and reduced physical performance, which can result in significant emotional distress.10,14-16 Coexisting symptoms (insomnia, disequilibrium, etc) can also affect the health and well-being of persons with neuropathic pain.17,18 Similar relationships may exist in cancer patients with neuropathic pain; however, these relationships have been understudied and warrant further investigation.19-21 In addition, little is known about how neuropathic pain differs from nonneuropathic pain with respect to pain severity and physical and emotional performance in persons with cancer. Important differences may exist that, if recognized, could lead to better pain management for all patients.
The purpose of this study was to explore differences in the experience of cancer patients who describe their pain using neuropathic descriptors (numbness, tingling, or electric-like sensations) compared with those who do not use these descriptors. The following research question guided this study: How does the experience of cancer patients with numbness, tingling, and electric-like sensations differ from the experience of other cancer patients with respect to pain, physical symptoms, health-related quality of life, and depressive symptoms?
Symptoms of neuropathic pain vary greatly from person to person. Numbness, tingling, and electric-like pain are descriptions repeatedly used within the literature to describe neuropathic pain and are thought to be unique to neuropathic pain because their presence indicates neuronal dysfunction.22 Numbness, tingling, or electric-like are unlikely to be used to describe pain of nonneuropathic origin. Therefore, this study looks at numbness, tingling, and electric-like sensations as indicators of neuropathic pain.
Muscle weakness, problems with concentration, and dizziness/lightheadedness represent potential motor and autonomic symptoms that may co-occur with neuropathic pain and interfere with physical and emotional well-being. Because these symptoms may share an underlying neuropathic etiology, more information regarding the prevalence of these symptoms in persons with cancer is needed. Sleep has also been identified as a significant problem in persons with cancer as well as persons with peripheral neuropathy.15,23
Study Methods
The data for this study were extracted from data collected for a National Institute of Nursing Research-funded study entitled "Coping With Pain: A Problem-Solving Approach for Caregivers of Cancer Patients" (R01 NR008270-04). The purpose of the parent study was to evaluate a psychoeducational intervention for caregivers of cancer patients with pain.
The focus of the parent study was to support family caregivers of patients experiencing cancer pain. The authors of the current study sought to learn more about the experiences of patients experiencing pain, particularly those with pain with a neuropathic component. Only data from the first set of patient questionnaires, collected upon agreement to participate in the study, were included in this secondary analysis.
Sample and Setting
The sample of 234 outpatients with cancer was accrued at Moffitt Cancer Center, a large National Cancer Institute-designated comprehensive cancer center in Tampa, Florida. Participants were recruited from all outpatient clinics at the cancer center. Inclusion criteria included a diagnosis of cancer and pain severity level of at least 3 on a 0- to 10-point scale. Patients had to be at least 18 years old, have at least a sixth-grade education, and have no documented neurological or psychiatric disorders. Patients were excluded if they were unable to read and understand English or were receiving hospice or home health care services. A sample of 345 participants was sought for the parent study; however, accrual was limited by time and patient and caregiver refusals.
Instruments
The instruments used for this study included the Memorial Symptom Assessment Scale (MSAS), Medical Outcomes Study-Short Form (MOS SF-36), and the Center for Epidemiologic Studies Scale-Depression (CES-D) and a revised version of the Brief Pain Inventory (BPI). Demographic data including age, sex, race and ethnicity, marital status, religious preference, income, employment status, type of cancer, and stage of cancer were collected.
BRIEF PAIN INVENTORY-REVISED
Pain severity and pain interference were assessed using a revised version of the BPI (BPI-R). Brief Pain Inventory-Revised assesses pain severity with 4 items that ask about present pain, pain at its worst, pain at its least, and on average using a 0- to 10-point scale.24,25 A 7-item interference subscale assesses pain's interference with daily functioning. Participants are asked to rate on a scale of 0 to 10 how much in the past week pain has interfered with general activity, mood, walking ability, normal work, relationships with other people, sleep, and enjoyment of life. Subscale scores range from 0 to 70. Significant correlations of the interference subscale with functional impairment and mood disturbance items from the Profile of Mood States provide evidence of validity. Cronbach [alpha]'s ranged from .86 to .91. Test-retest reliability was strong in previous studies.26 The pain severity items and interference items in the BPI-R are identical to the same items on both the long and short forms of the original BPI.27,28
The long version of the BPI contains a list of 15 pain descriptors that patients may use to describe pain.28 Three descriptors were added (tingling, electric-like, and dull) for the parent study to allow differentiation of pain into nociceptive and neuropathic. The BPI-R asked patients to circle as many of the following words as needed to fully describe their pain: aching, throbbing, shooting, stabbing, gnawing, tingling, sharp, tender, burning, exhausting, tiring, electric-like, penetrating, nagging, numb, miserable, unbearable, and dull. Patients were also asked if pain was continuous or intermittent and how long (in months) had they had this pain.
MEMORIAL SYMPTOM ASSESSMENT SCALE
The MSAS was used to assess select physical symptoms that have been previously identified in persons with neuropathic pain: muscle weakness, sleep problems, problems with concentration, and dizziness/lightheadedness.29 The MSAS was designed to assess symptoms commonly associated with cancer in 3 dimensions: (1) severity of the symptom, (2) frequency with which it occurs, and (3) the distress it produces. For this study, only data regarding the presence, severity, and distress of selected items were used in the analysis. Scores for severity and distress range from 0 to 3, with higher scores indicating higher severity or distress.29,30
Validity and reliability data for the original MSAS have been strong in persons undergoing cancer treatment.29 Factor analysis confirmed 2 factors that distinguished 3 major groups of symptoms. The 3 confirmed groups of symptoms were psychological, high-prevalence, and low-prevalence physical symptoms. Reliability coefficients indicated strong internal consistency for the subscales ([alpha] = .83-.92).
MEDICAL OUTCOMES STUDY-SHORT FORM
Health-related quality of life was measured using MOS SF-36, a 36-item self-report measure that assesses 8 health-related concepts.31 Four of the 8 subscales assess physical well-being, and 4 assess emotional well-being. Physical subscales include physical functioning, role limitations due to physical health problems, bodily pain, and general health. These 4 subscales combine to form a physical component score. Emotional subscales include vitality, social functioning, role limitations due to emotional problems, and mental health.32 These 4 subscales combine to form a mental component score. Higher scores indicate higher levels of functioning. The MOS SF-36 has undergone extensive psychometric testing and has been widely used in studies involving individuals with cancer. Test-retest reliability coefficients for the subscales range from .68 to .93, and internal consistency reliability results range from .52 to .78.
CENTER FOR EPIDEMIOLOGIC STUDIES SCALE-DEPRESSION
The CES-D is a 20-item self-report scale that assesses current depressive symptoms. Scores range from 0 to 60, with higher scores indicating more depressive symptoms. Scores greater than 16 on the CES-D are associated with high levels of psychological distress.33 The CES-D is a widely used scale that has proven useful in measuring the symptoms of depression. The CES-D has been translated into multiple languages and has impressive reliability and validity. Factor analysis confirmed the structure of the scale. Cronbach [alpha]'s were .85 for the general public and .85 to .91 in persons with cancer, indicating strong reliability.34-36
Procedures
The study was approved by the Protocol Research Monitoring Committee at the Cancer Center and the institutional review board of the University of South Florida. For the parent study, potential participants with a scheduled appointment were identified for eligibility through clinician referral and review of the medical record. Participants who were determined to be eligible were invited to participate and then consented and randomized into an intervention group or a control group who received usual care. The intervention consisted of three 1-hour sessions and 2 brief follow-up calls with caregivers over a 12-week period. Topics included pain assessment, managing adverse effects of pain medications, communication with health care providers, coping techniques, and stress management. Patients and caregivers were asked to individually complete separate questionnaire packets at 3 time intervals: one upon consent to participate, another at 6 weeks after the beginning of the study, and finally at 12 weeks after the beginning of the study. Participants were reimbursed $25 per questionnaire packet completed.
Data Analysis
The intervention and control groups were combined, and baseline data from both groups were analyzed. Data from the first set of patient questionnaires were included. The sample was divided into 2 groups using pain descriptors reported on the BPI-R. Patients who reported 1 or more of the following pain descriptors: numbness, tingling, or electric-like, were grouped together and compared with a group of patients who did not use any of those 3 descriptors to describe their pain. This approach to grouping participants was based on the current literature that consistently identifies numbness, tingling, and electric-like sensations as terminology consistent with a neuropathic pain component and provided a logical method for the researchers to examine neuropathic pain within the context of the parent study.
Demographic data were analyzed using descriptive statistics including frequencies, percentages, means, and SDs. Differences between means were analyzed to determine differences between patients with numbness, tingling, or electric-like sensations and patients who did not report these symptoms. A series of independent t tests were used to determine differences in pain levels, pain interference, length of pain, health-related quality of life, severity and distress levels of muscle weakness, sleep problems, problems with concentration, and dizziness/lightheadedness. Bonferroni adjustments were used because multiple comparisons were made. A series of [chi]2 tests were analyzed to determine differences in number of participants in each group reporting muscle weakness, sleep problems, problems with concentration, and dizziness/lightheadedness, disability, and continuous versus intermittent pain. A power analysis was conducted prior to this analysis to determine adequacy of the existing sample size. Estimating a medium estimated effect size, a total of 128 patients (64 patients in each group) were needed to achieve 80% power with 2-sided 5% significance level.
Results
Sample
Data describing the demographic characteristics of the sample were analyzed. The sample was almost equally divided between men and women, who were predominantly white and married (Table 1). A majority was Christian, either non-Catholic or Catholic, and was retired or disabled. Annual family incomes ranged from less than $10 000 to more than $100 000. Patients had a mean age of about 56 (SD, 12.8) years and ranged in age from 24 to 84 years. They reported an average of 13 (SD, 2.3) years of formal education and had a variety of cancer diagnoses including solid tumors and hematologic malignancies, Most had stage III or IV disease and were receiving chemotherapy or radiation therapy (Table 2).
Eighty-five participants (36%) were in the group who reported numbness, tingling, or electric-like pain, and 149 (64%) participants were in the comparison group. In the group reporting numbness, tingling, or electric-like pain, 54% (n = 46), used 1 of the 3 included descriptors, 34% (n = 29) used 2 of the 3 descriptors, and 12% (n = 10) used all 3 of the included descriptors. Patients in both groups had similar ethnicity, income, education, religion, and marital status. Patients with numbness, tingling, or electric-like sensations (mean, 54 [SD, 13.8]) were an average of 4 years younger than patients who did not report these pain characteristics (mean, 58 [SD, 11.91] years) (t192 = 2.12, P = .034).
Analysis of data from the demographics questionnaire revealed that patients who reported numbness, tingling, and electric-like sensations were more likely to be disabled. Disability was reported in 51% of patients with numbness, tingling, or electric-like sensations compared with 30% of patients without these symptoms, [chi]21 (N = 234) = 9.6, P = .003.
Pain
Pain and pain interference were assessed using data from the BPI-R to identify differences in severity and interference with performance. Patients with numbness, tingling, or electric-like sensations reported significantly higher levels of current pain severity (P = .001), pain at its worst (P = .001), pain on average (P = .019), and pain at its least (P = .008) (Table 3). Patients with numbness, tingling, or electric-like sensations were more likely to report continuous instead of occasional pain, [chi]21 (N = 234) = 8.6, P = .004. Pain duration in months was almost twice as long for patients with numbness, tingling, or electric-like sensations (mean, 36.7 [SD, 66.3] months) than for patients who did not report these pain characteristics (mean, 17.4 [SD, 42.2] months). Patients with numbness, tingling, or electric-like sensations reported greater pain interference with general activity, walking ability, normal work, sleep, mood, relationships with other people, and total pain interference (Table 4). Differences in pain interference with enjoyment of life were nonsignificant.
Symptoms
Muscle weakness, dizziness/lightheadedness, problems with concentration, and problems with sleep were assessed using individual items from the MSAS to determine differences in the symptom experience between the 2 groups. Patients with numbness, tingling, and electric-like sensations reported problems with dizziness/lightheadedness significantly (P = .004) more often than did patients who did not report these pain characteristics (Table 5) and also reported more severe problems with concentration (P = .047). No significant differences in occurrence of muscle weakness, sleep problems, or problems with concentration were found. No significant differences in severity or distress of muscle weakness, dizziness/lightheadedness, or problems with sleep were found among those who reported the symptoms in each group.
Health-Related Quality of Life
Differences in health-related quality of life were assessed using data from the MOS SF-36. Patients with numbness, tingling, or electric-like pain had significantly (P = .003) more bodily pain and perceived their general health as poorer (P = .009), had more role limitations due to physical health problems (P = .001), and had lower scores for vitality (P = .008). Differences in emotional role functioning indicate that patients with numbness, tingling, or electric-like sensations have more difficulty (P = .003) performing regular daily activities as a result of emotional distress (Table 6). Physical (P = .019) and mental (P = .024) component scores were significantly lower in patients with numbness, tingling, or electric-like pain.
Depressive Symptoms
Differences in depressive symptoms were assessed using data from the CES-D. This study found no significant differences in depressive symptoms. Both groups reported high levels of depressive symptoms. The mean CES-D score for patients without numbness, tingling, or electric-like sensations was 18.96, whereas the mean score for patients with these characteristics was 20.38. Center for Epidemiologic Studies Scale-Depression scores were negatively correlated with MOS SF-36 mental component scores (r = 0.404, P < .001), indicating that as depressive symptoms increase, mental health decreases.
Discussion
Sample
In this sample, 36% of patients reported numbness, tingling, or electric-like pain, which are characteristics typically associated with neuropathic pain. This high incidence of neuropathic pain characteristics among outpatients with moderate to severe pain suggests that control of neuropathic pain continues to be problematic, even in facilities whose entire mission is to care for the needs of cancer patients. Literature supports the use of agorithms and treatment guidelines as effective in alleviating neuropathic pain but requires close communication between clinicians and patients as well as ongoing assessment.8,37
The higher incidence of disability among the patients with numbness, tingling, or electric-like sensations, along with the findings that these patients report more interference and poorer health-related quality of life, indicates that neuropathic pain has a strong influence on patients' ability to maintain their usual lifestyle and activity level. Patients with neuropathic pain may have coexisting neurological symptoms such as loss of balance, muscle weakness, loss of manual dexterity, and loss of fine motor coordination that contributed to the high incidence of disability and functional deficits in this study.17,19,20,38 Such symptoms limit physical performance and may also prevent people from being able to perform essential job responsibilities.
This study did not thoroughly evaluate nonpainful symptoms of a neuropathic origin, but future studies should focus on evaluation of both painful and nonpainful neuropathies. In our study, disability was measured by a single item on the demographic questionnaire, but the findings from the MOS SF-36 physical and emotional role limitations subscales and the BPI-R interference scale also indicate that patients with neuropathic pain have significantly more difficulty performing in their usual roles. These findings support the results of earlier literature documenting relationships between neuropathy and physical disability.15,20,39,40
Pain
The study confirms that patients in our sample with numbness, tingling, or electric-like sensations report more intense current pain, least pain, average pain, and worst pain and report continuous pain more often. They also had more pain interference with general activity, walking ability, normal work, sleep, relationships with people, and mood. Insignificant differences in enjoyment of life probably reflect the myriad of issues that cancer patients face that impact their enjoyment of life, including pain.
Similar findings have been demonstrated in persons with chronic pain from a variety of causes, where pain that was considered predominantly neuropathic in origin was found to be significantly more severe and debilitating than nonneuropathic pain.14 Previous studies of patients with peripheral neuropathy have also demonstrated high levels of pain severity that interfere with both physical and mental functioning.15 These findings again highlight the need for aggressive pain management in cancer treatment, including differentiating the source of the pain so that individuals with neuropathic pain can be reliably identified and treated more appropriately. More research evaluating treatment approaches for neuropathic pain is needed, and health care professionals need ongoing education focusing on assessment and treatment of neuropathic pain.
One limitation of the study is the lack of clinical assessment of pain. Future studies should include evaluation by a clinician trained to properly differentiate between nonneuropathic and neuropathic pain or verify mixed pain syndromes. A second limitation of the study was that the BPI-R had not previously been validated to differentiate between neuropathic and nonneuropathic pain as was done in this study. However, results show significant differences between the 2 groups, which offer beginning support for the validity of this use. Further research in this area is needed.
Symptoms
Analysis of selected symptoms including muscle weakness, sleep problems, problems with concentration, and dizziness/lightheadedness showed that dizziness/lightheadedness was more prevalent, and severity of problems with concentration was more severe in patients with numbness, tingling, or electric-like sensations. Dizziness/lightheadedness and problems with concentration may also reflect symptoms of neuropathy.41 Previous studies have identified relationships between neuropathic pain and sleep in noncancer populations15,23 and muscle weakness in cancer patients,42,43 but no differences in these symptoms were demonstrated in this study. Patients with documented neurological disorders were excluded from the study, which may have affected these results, because patients with previously diagnosed neurological disorders may have been more likely to experience these symptoms.
Dizziness and lightheadedness may contribute to falls, and problems with concentration may also compromise patients' ability to maintain safety within the home. Interventions aimed at promoting safety and minimizing fall risk should be initiated and reevaluated at regular intervals because symptoms may worsen quickly.41 Instruments are available to help evaluate neuropathic symptoms.19,22,44-48 These instruments should be widely utilized along with physical assessment, in clinical practice, to gain a better understanding of how neuropathic pain is influencing patients' lives and make appropriate recommendations and referrals.
Health-Related Quality of Life
Results of this study indicate that patients with neuropathic symptoms (numbness, tingling, and electric-like sensations) have poorer health-related quality of life than those without these characteristics. Patients with numbness, tingling, or electric-like sensations had significantly greater physical and role limitations and reduced vitality. They also had more bodily pain and perceived their general health as poorer. These findings indicate that patients with neuropathic pain have less energy, are more socially isolated, and experience more physical and psychological distress. Again, these results support the findings of earlier studies that demonstrate that patients with chronic neuropathic pain have poorer health-related quality of life than that of patients with nonneuropathic pain.14 These results also further support the use of the BPI-R to group patients into neuropathic and nonneuropathic pain groups.
Nurses should be cognizant of the profound impact that neuropathic pain can have on health-related quality of life, including physical and mental functioning. Nursing interventions should focus on relieving pain and improving functional status. Maintaining independence and improving physical and emotional well-being are important goals that patients and clinicians can work toward together.
Depressive Symptoms
Mean scores for depressive symptoms were higher in patients with numbness, tingling, or electric-like sensations, although differences were not statistically significant. Measurement of depression may be confounded by the physical symptoms that cancer patients experience. This may have occurred in our study as scores are higher than those in previous studies involving persons with cancer. Higher scores in this study may also have been related to the fact that all the patients had at least moderately severe pain.34,49 The results support previous findings of high levels of depressive symptoms in persons with chronic pain.15,23 Negative correlations between CES-D scores and MOS SF-36 mental component scores support validity of the CES-D in this study.
In addition to chronic pain and cancer-related symptoms, loss of independence, financial pressures, and strained relationships all contribute to depressive symptoms in cancer patients.50 It is important for health care professionals to assess for psychological distress and depressive symptoms, take time to listen to concerns, and provide emotional support. Nurses may be the first to recognize depressive symptoms and initiate appropriate referrals to mental health professionals.
Limitations
Several limitations in the sample were found. The sample was not large; there was a very small sample of minority patients; all had to be able to read and understand English, which eliminated several minority patients; and all came from 1 cancer center in a single geographic location. Future studies should include more ethnically and geographically diverse samples. Because the larger study from which these data were taken required patients to have a family caregiver, patients with no spouse were less likely to be included. The presence of an available family caregiver might have biased the results in some unknown ways.
Previous researchers differentiated between neuropathic pain and nonneuropathic pain using pain descriptors from the McGill Pain Questionnaire with mixed results.9,51,52 Further research using the descriptors included in this study is needed. Although numbness, tingling, and electric-like sensations are believed to reflect neuropathic pain, and the literature confirms the use of these terms, it is possible that there were patients with neuropathic pain who did not report numbness, tingling, or electric-like sensations. Pain description should be combined with clinical assessment to identify underlying pain mechanisms. It is not uncommon for patients to simultaneously experience 2 or more types of pain.53 Because only the presence of specific characteristics was examined as indicators of neuropathic pain, it is likely that the percentage of patients with neuropathic pain was underestimated in this study.
Conclusions
The results of this study indicate that cancer patients with numbness, tingling, or electric-like sensations have significantly higher levels of pain and pain interference and lower health-related quality of life than do patients without these symptoms. No significant differences in depressive symptoms were detected, although relatively high levels of depressive symptoms were identified in both groups. When evaluating patients with severe pain, the possibility of a neuropathic component should be considered, because neuropathic pain requires a different approach to treatment.37,54,55 These results highlight the ongoing need for research evaluating methods of treating neuropathic pain, education regarding assessment and management of neuropathic pain, and aggressive efforts to relieve neuropathic pain in oncology settings. Better control of neuropathic pain may positively influence quality of life and improve physical and emotional well-being in persons with cancer.
References