Volume 36, Issue 2 , Pages 167-172, August 2008
Sex Differences in the Adequacy of Pain Management Among Patients Referred to a Multidisciplinary Cancer Pain Clinic
Article Outline
Abstract
Few studies have evaluated sex differences in the adequacy of pain management in cancer. Existing studies have been marked by methodological limitations and results have been mixed. The present study sought to determine whether sex was associated with pain severity and pain management in cancer patients newly referred by their primary oncology team to a multidisciplinary cancer pain clinic. One hundred thirty-one cancer patients completed the Brief Pain Inventory-Short Form and medical chart review was conducted to obtain patients' clinical characteristics and pain treatment data. There were no differences between males and females in ratings of worst pain in the last week. Females were significantly less likely to have been prescribed high potency opioids by their primary oncology team and significantly more likely to report inadequate pain management as measured by Pain Management Index scores. These results suggest a sex bias in the treatment of cancer pain and support the routine examination of the effect of sex in cancer pain research.
Key Words: Pain, cancer, pain management, sex differences
Introduction
Despite the prevalence of pain in cancer,1 pain is often undertreated.2, 3, 4, 5 Research suggests that patient characteristics, such as minority status or less educational achievement, are associated with an increased likelihood of having pain inadequately treated.6, 7, 8, 9 Other patient characteristics, including sex, have not been as widely evaluated in studies of cancer pain patients.10 That research on the effect of sex on cancer pain and pain management is limited is particularly noteworthy given the fact that studies have suggested sex differences in pain sensitivity and tolerance,11, 12 response to analgesic medications,13, 14 and pain treatment outcomes.15
To date, the results of existing research examining the effect of sex on the treatment of pain in cancer have been mixed. For example, in a descriptive, cross-sectional study, Cleeland et al.3 described the treatment of pain in 1,308 outpatients with metastatic cancer. Results indicated that females were 1.5 times more likely to report inadequate pain management based on Pain Management Index (PMI) scores.3 The researchers did not report whether there were sex differences in reported pain severity or in the analgesic medication doses prescribed, however. Strömgren et al.16 examined pain control in 175 patients with advanced cancer referred for palliative care. Males and females did not differ in reported pain severity. Although the researchers compiled data on analgesic medications, including equianalgesic doses, they did not examine whether there were sex differences related to the adequacy of pain management. Edrington et al.17 assessed the severity and management of pain in 187 cancer outpatients with pain from bone metastases. There were no sex differences in pain severity, analgesic doses prescribed, or the adequacy of pain management based on PMI scores.
Given the paucity of existing research examining the effect of sex on pain management in cancer, as well as a lack of consistency among what medication data are reported and how, it is difficult to draw definitive conclusions about potential sex differences. Only Edrington et al.17 reported detailed information about analgesic doses prescribed, as well as PMI scores. The Edrington et al.17 study included a heterogeneous sample of cancer patients and there was considerable variability in the analgesic doses prescribed; both of these factors may have affected their ability to detect a sex effect and likely limited the generalizability of the results. Further research is warranted because existing studies have lacked methodological consistency in how potential sex differences in pain management have been examined.
The purpose of the present study was to evaluate whether sex was associated with the adequacy of pain management in patients newly referred to a multidisciplinary cancer pain clinic. We also were interested in examining whether other demographic factors, such as age and education, and other clinical factors, such as stage of disease, were associated with patients' pain severity and the adequacy of pain management.
Materials and Methods
Participants
Participants were individuals with a diagnosis of cancer referred by their primary oncology team at the Moffitt Cancer Center at the University of South Florida to the multidisciplinary cancer pain clinic within the Moffitt Cancer Center. Pain management services are available to cancer patients who are in active treatment or who are being seen for routine surveillance by their primary team. There are no formal criteria for making a referral; referrals are typically made when the primary team believes the patient needs more specialized pain management services or when the patient requests that the referral be made. Specific eligibility criteria for the study were that participants: (a) be at least 18 years of age, (b) have no documented or observable psychiatric or neurological disorders that would interfere with study participation (e.g., dementia or psychosis), (c) be able to speak and read standard English, and (d) provide written informed consent.
Procedure
The Institutional Review Board at the University of South Florida approved the study. Eligible participants were identified through the computerized appointment system at the Moffitt Cancer Center. Approximately two weeks prior to their scheduled pain clinic appointment, patients were mailed an introductory letter and packet of self-report questionnaires. A toll-free number was included and patients were asked to leave a message at this number if they did not wish to participate. Patients were contacted by telephone two days before their scheduled appointment to determine whether or not they would be willing to complete the questionnaires and bring the packet with them to their appointment. At their appointment, written informed consent was obtained and the completed questionnaires were collected.
Of the 161 patients who met eligibility criteria and agreed to participate, 131 (81%) completed the assessment just prior to their multidisciplinary cancer pain clinic appointment.
Measures
Demographic Data. Demographic data were obtained via a standard self-report questionnaire. Variables assessed were sex, age, race/ethnicity, marital status, annual household income, and education level.
Clinical Data. Clinical data were obtained via a self-report form and confirmed by medical chart review. Variables assessed were cancer diagnosis, date of diagnosis, disease stage, type of treatments to date, and current medications. Opioid medications were converted to their daily morphine equivalent values18 and the total daily doses were calculated.
Pain. The Brief Pain Inventory-Short Form (BPI-SF)19, 20 is a self-report measure of pain that measures the severity and location of pain and pain's interference in various domains of daily functioning. The BPI-SF has demonstrated both reliability and validity in the assessment of pain in cancer patients as well as studies of the effectiveness of pain treatment.20
Pain Management Index. The PMI3 assesses the adequacy of the management of a patient's pain by associating the pain medication prescribed by the health care provider to the patient's reported level of pain. Analgesic drug therapy is rated on a four-point scale (0
=no analgesic drug, 1=a nonopioid, 2=a “weak” opioid, and 3=a “strong” opioid). The patient's level of pain is determined from the worst pain score on the BPI-SF (1–3=mild, 4–7=moderate, 8–10=severe). The absence of pain is then scored as 0, mild pain as 1, moderate pain as 2, and severe pain as 3. The PMI is computed by subtracting the pain level from the analgesic level (range, −3 to +3). Negative scores reflect inadequate pain management whereas a score of zero or greater reflects adequate pain management.
Results
Demographic and Clinical Characteristics
Descriptive statistics were used to characterize the demographic and clinical characteristics of the sample. Potential sex differences in these characteristics were examined using Chi-square tests for categorical variables (e.g., marital status) and analyses of variance for continuous variables (e.g., age). As shown in Table 1, female patients were significantly younger than male patients, less likely to be married, and less likely to have annual household incomes equal to or greater than $40,000 (P values <0.05). There were no differences between male and female patients in race or education. The mean time since diagnosis was approximately 3.5 years, and on average, females had a significantly longer time since diagnosis than males (P=0.03). Based on these results, age, marital status, income, and time since diagnosis were included as covariates in subsequent analyses examining sex differences in pain severity, analgesic medications prescribed, and PMI scores.
Table 1. Demographic and Clinical Characteristics of the Sample
| Females (n=82) | Males (n=49) | P -Value | |
|---|---|---|---|
| Years of Age; M±SD | 54.33±13.0 | 59.59±13.8 | 0.03 |
| Race/Ethnicity | |||
| % Caucasian | 96.3 | 93.9 | 0.51 |
| Education | |||
| % college degree | 37.8 | 34.7 | 0.72 |
| Marital Status | |||
| % married | 68.3 | 87.7 | 0.01 |
| Annual household income | |||
| % ≥$40,000 | 47.6 | 65.3 | 0.05 |
| Years since diagnosis | |||
| M±SD | 4.05±4.2 | 2.51±2.9 | 0.03 |
| Diagnosis (%) | |||
| Breast | 34 | ||
| Ovarian | 12 | ||
| Head and neck | 4 | 25 | |
| Colorectal | 9 | 12 | |
| Hematologic | 6 | 12 | |
| Urologic | 2 | 18 | |
| Other | 33 | 33 | |
| Disease stage (%) | |||
| I | 25 | 14 | 0.59 |
| II | 25 | 25 | |
| III | 28 | 39 | |
| IV | 22 | 22 | |
| Treatment to date (%) | |||
| Surgery | 76 | 61 | 0.58 |
| Radiation | 52 | 65 | |
| Chemotherapy | 65 | 71 | |
In terms of cancer diagnosis, a heterogeneous mix of cancers was represented; the “other” category in Table 1 includes 17 different cancers. The most common diagnosis among females was breast cancer (34% of females) while the most common diagnosis among males was head and neck cancer (24% of males). To account for the potential confounding effect of the large number of breast cancer patients in the sample, we compared the pain severity ratings of these women with the pain severity ratings of women with other cancer diagnoses, as well as with the remainder of the sample. In analyses of variance, there were no significant differences in worst pain, least pain, average pain, or pain right now between breast cancer patients and other female cancer patients or between breast cancer patients and the other participants. Similarly, inadequate pain management was not specifically associated with a breast cancer diagnosis. We used the same approach to account for the potential confounding effect of the relatively large number of male head and neck cancer patients and likewise found that head and neck cancer was not significantly associated with greater pain ratings or with inadequate pain management.
Pain Severity and Pain Interference
As shown in Table 2, in analyses of variance there was not a significant difference between males and females in worst pain scores, least pain scores, or pain interference on the BPI-SF, but females reported significantly higher scores for average pain in the last week and pain right now (P-values <0.05).
Table 2. Patient-Reported Pain Severity and Pain Interference Scores
| Females (n=82) | Males (n=49) | P-Value | |
|---|---|---|---|
| Worst pain | 7.51±2.34 | 7.59±2.23 | 0.84 |
| Least pain | 3.93±2.56 | 3.12±2.25 | 0.07 |
| Average pain | 5.89±2.22 | 4.96±1.95 | 0.02 |
| Pain right now | 5.54±2.67 | 4.49±2.36 | 0.03 |
| Pain interference | 6.24±2.40 | 5.83±2.24 | 0.34 |
Given that PMI scores are calculated using worst pain scores in the past week on the BPI-SF, we also conducted analysis of variance with continuous variables or Chi-square test with categorical variables to examine the relationship between worst pain and the other demographic and clinical characteristics. Age, education, marital status, income, stage of disease, and type of treatment were not significantly associated with worst pain severity scores.
Analgesic Medications
Table 3 presents data on analgesic medications. The mean total daily morphine equivalent dose for the sample was 89.89±156.64mg. In analysis of variance, the mean total daily dose was significantly greater for males than for females (P=0.03). No other demographic or clinical characteristics were associated with the mean total daily dose.
Table 3. Prescribed Analgesic Medications
| Females | Males | P- Value | |
|---|---|---|---|
| Mean total daily dose (morphine equivalent value) | 66.14±128.2 | 130.32±190.6 | 0.03 |
| Non-opioid analgesics | 41.5% | 30.6% | 0.21 |
| Low potency opioids | 29.3% | 32.7% | 0.68 |
| High potency opioids | 32.9% | 51.0% | 0.02 |
| Adjuvant analgesics | 30.5% | 27.1% | 0.68 |
Types of medications prescribed were not mutually exclusive in that patients may have been taking more than one type of pain medication. Thirty-five percent were taking no opioids. As shown in Table 3, in Chi-square analysis, females were significantly less likely than males to be taking high potency opioids (P=0.02). With respect to other demographic and clinical characteristics, compared to patients with more education, patients with less education were more likely to be taking low potency opioids (P=0.009). Type of treatment and disease stage were not associated with the types of analgesic medications being taken by the sample.
Pain Type
The most frequently reported type of pain was neuropathic pain (58.8%). Approximately half of the sample (52.6%) reported somatic pain, 32.7% reported visceral pain, and 10.5% reported headaches. Types of pain reported were not mutually exclusive in that patients could have reported experiencing more than one type of pain. In Chi-square analysis, sex was not associated with type of pain reported. The only demographic characteristic associated with type of pain was age; younger patients were more likely to report headaches (P=0.004). With respect to clinical characteristics, time since diagnosis, type of treatment, and disease stage were not significantly associated with type of pain reported. More advanced stage of disease was marginally associated with the presence of visceral pain (P=0.06).
Pain Management Index
PMI scores for the sample ranged from −3 to +2 (see Table 4). Nearly half of the sample (46.5%) had PMI scores less than 0. Among those patients reporting adequate pain management, the vast majority (78.6%) had PMI scores equal to 0. Using the nonparametric Mann–Whitney U test, females were significantly more likely than males to report inadequate pain management on the ordinal level PMI (P=0.04), and in logistic regression, there was a significant sex effect (P=0.005) even after controlling for age, marital status, income, and time since diagnosis.
Table 4. Pain Management Index Scores for the Sample
| Femalesa % | Males % | |
|---|---|---|
| −3 | 13.6 | 14.3 |
| −2 | 14.8 | 8.2 |
| −1 | 27.2 | 8.2 |
| 0 | 35.8 | 53.1 |
| +1 | 6.2 | 16.3 |
| +2 | 2.5 | 0.0 |
aMann-Whitney U |
There were no other demographic characteristics associated with inadequate pain management. With respect to clinical characteristics, patients who underwent surgical treatment were more likely to report inadequate pain management (P=0.006).
Discussion
Results from the current study indicate that female and male cancer patients referred to a multidisciplinary cancer pain clinic by their primary oncology team did not differ in their self-report of worst pain severity. This is consistent with previous research among cancer pain patients.16, 17, 21 Results also indicated sex differences in the prescription and dosing of analgesic medications and the adequacy of pain management based on PMI scores. Females were less likely to be prescribed strong opioids and less likely to have their pain adequately managed. This is consistent with the finding by Cleeland et al.3 that female sex was associated with a greater likelihood of inadequate pain management.
None of the other demographic or clinical characteristics assessed were associated with worst pain severity. Given the greater likelihood of pain in metastatic disease, one might have expected that more severe pain would be associated with more advanced stage of disease and with a longer time since diagnosis if this suggests progressive disease. That this was not the case may be attributable to the nature of the sample included in the study. The patients had been referred for pain management by their primary oncology team. On average, their pain scores were quite high, and the average time since diagnosis was more than three years. Although we did not assess how long each patient had been experiencing pain, it may be that as time went on, patients' pain became more chronic in nature and eclipsed the primary team's ability to adequately manage their pain.
In terms of the adequacy of pain management, less education was the only other demographic characteristic, besides female sex, that was associated with the type of opioid medication prescribed. Just as the primary team's ability to manage patients' severe pain may have been limited, patients with less education may have been perceived by the primary team as less able to cope with the increased complexity of strong opioids to optimize pain control. The only clinical characteristic associated with adequacy of pain management was surgical treatment. Although the reason for this is not clear, more than two-thirds of patients underwent surgery as part of their cancer treatment, and this result may reflect the long-term after-effects of extensive surgical resection.
This study is one of the few to examine sex differences in cancer-related pain management; thus, limitations of the study should be noted. The majority of patients was Caucasian and well educated, with more than half reporting incomes greater than $40,000. The sample size was small. Although the sample as a whole was homogeneous in terms of demographics, the sample was clinically quite diverse. There were many different cancer diagnoses, and the full range of disease stages was represented. Finally, although we examined the effect of time since diagnosis on pain reports, we did not assess whether the pain reported was acute or chronic in nature.
Our findings that females were less likely to be prescribed strong opioids by their primary oncology team and more likely to experience inadequate pain management based on PMI scores suggest a sex bias in the treatment of cancer pain. Although this possibility has not been widely evaluated in the cancer pain literature, other researchers have found evidence of a sex bias in the treatment of chronic pain in other medically ill patients.22 In the absence of a sex bias, there are other possible explanations for our findings. There may have been sex differences in how participants communicated the severity of their pain to their primary oncology team. Women may have differed in their perceptions of and response to pain such that they were more likely than men to seek a referral for specialized pain treatment. There may have been sex differences in preferences for opioid medication. Women may have been more likely to prefer weak opioids and less likely to be prescribed strong opioids due to a greater likelihood of experiencing opioid-related side effects. Despite the current study's limitations, the findings indicate the need to improve the treatment of pain in ambulatory cancer patients and to more closely examine physician and patient-related factors that may hinder adequate pain management. The findings also support the routine examination of the effect of sex in future cancer pain research.
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PII: S0885-3924(08)00108-5
doi:10.1016/j.jpainsymman.2007.09.013
© 2008 U.S. Cancer Pain Relief Committee. Published by Elsevier Inc. All rights reserved.
Volume 36, Issue 2 , Pages 167-172, August 2008
