| | Illness and Demographic Correlates of Chronic Pain Among a Community-Based Sample of People With Multiple SclerosisAbstract Douglas C, Wollin JA, Windsor C. Illness and demographic correlates of chronic pain among a community-based sample of people with multiple sclerosis. ObjectiveTo investigate the prevalence, nature, and correlates of pain among a community-based sample with multiple sclerosis (MS). DesignA cross-sectional survey and structured pain interview. ParticipantsPeople with MS (N=219) recruited through systematic sampling from a randomly ordered MS society membership database. InterventionsNot applicable. Main Outcome MeasuresPain presence or absence, pain intensity (numeric rating scales), pain quality (McGill Pain Questionnaire), pain location(s) and extent (pain drawing), pain duration and frequency, provoking and relieving pain factors, and pain management techniques. ResultsPain was common with some 67.1% of the sample reporting pain during the 2 weeks preceding the study. Comprehensive pain assessment revealed that a substantial subset of these subjects experience chronic pain conditions characterized by moderate-to-severe pain intensity. Among those with pain, 75% reported pain in 3 or more locations, with participants reporting an average of 4.0±1.8 distinct pain sites. Women and people with more severe MS-related disability were significantly more likely to report both the presence of pain and greater pain intensity. In contrast, being in a married or in a de facto relationship and longer time since MS diagnosis were significantly associated with lower pain intensity. ConclusionsGiven the high prevalence and nature of pain experienced by people with MS, health care providers need to approach pain with a priority similar to that given to other MS-related problems such as mobility and functional independence. Women and people with more severe MS-related disability appear to be at particular risk for significant pain problems and therefore these groups warrant particular attention, such that routine clinical assessment should trigger routine pain assessment. List of Abbreviations: BPI, Brief Pain Inventory, CI, confidence interval, EDSS, Expanded Disability Status Scale, GNDS, Guy's Neurological Disability Scale, MPQ, McGill Pain Questionnaire, MS, multiple sclerosis, NRS, numeric rating scale, NSAID, nonsteroidal anti-inflammatory drug, OR, odds ratio, PRI, pain rating index ALTHOUGH EXTENSIVE literature exists on the nature of and treatments for chronic pain as a primary condition, little is known about the impact of chronic pain as a secondary problem in people who already have a disability such as MS.1, 2 Despite the paucity of literature on MS-related pain, it is evident that pain is a common problem over the course of the disease. Estimates of the prevalence of pain in MS range from as low as 29%3 to as high as 90%,4 with recent studies indicating that approximately two thirds experience pain.5, 6, 7 Thus, it is clear that pain affects a considerable proportion of the MS population. Beyond this consistent finding, however, the extant literature is extremely limited in size, scope, and methodology. Thus far, evidence concerning the relationship between MS-related pain and illness and demographic variables is inconclusive and contradictory. In several cross-sectional studies, the presence and intensity of pain was found to be independent of disease duration, age of disease onset, MS type, and level of disability.5, 6, 7, 8, 9, 10 In contrast, other investigators have found significant associations between the presence of pain and greater MS-related disability.11, 12, 13, 14 Sex differences were shown in 3 studies, with women reporting both increased frequency and intensity of pain.8, 15, 16 Yet, this finding was not replicated by others.7, 9, 10, 13, 14, 17 Similarly, although the prevalence of pain has been found to increase with age in several studies,3, 6, 8, 15, 17 this finding is not always supported.7, 9, 10, 14 General conclusions have been limited by several factors. First, the majority of research is based on small, convenience samples presenting to MS-specific clinics or hospital departments and therefore findings may not generalize to the wider MS population. Second, there is no consensus within the literature about the classification or definitions of MS-related pain. For example, researchers have adopted different timeframes for classifying specific types of pain. Further, the arbitrary exclusion of various pain conditions (eg, headaches, optic neuritis) in some studies makes comparisons difficult. Third, idiosyncratic methods of pain measurement are common and most researchers failed to use standardized pain assessment tools routinely used in the pain literature. Most authors devised specific questionnaires, the particular content or psychometric properties of which are not routinely reported. Last, the level of statistical analysis was most often at the univariate or bivariate level. Few researchers used multivariable modelling to examine complex relationships and to control for likely confounding variables. In summary, MS-related pain is a significant problem that has historically been underinvestigated and is currently poorly understood. The vast majority of the published literature consists of prevalence studies, descriptive research, and clinical reports. Where available, empirical data are often limited by methodologic and analytical problems such that substantive conclusions about the scope and nature of MS-related pain remain unclear. To redress these deficiencies and provide a valid and detailed assessment of MS-related pain in the community, the following research questions were addressed in the present study: (1) What is the prevalence and nature of pain experienced by people with MS? (2) What illness and demographic variables are associated with the presence and intensity of MS-related pain? Methods  Participants We sent questionnaires by post to a community-based sample of people with MS (N=500) recruited from the Multiple Sclerosis Society of Queensland membership database. There is estimated to be approximately 3000 people with MS in Queensland, 2139 being registered clients of the Multiple Sclerosis Society of Queensland. Of these, approximately 1200 people met the eligibility criteria of the study. Systematic random sampling was performed such that from a randomized membership roll, every third person was selected to a total of 500. Participant eligibility criteria were (1) chronologic age 18 years or older, (2) definite diagnosis of MS confirmed by their neurologist, (3) residents of Queensland within a 2-hour drive from Brisbane, to define a geographic area able to be covered by the researcher within the scope of the study, (4) fluency of English and therefore able to read and complete the questionnaire battery and participate in the pain interview, and (5) able to follow instructions and complete the self-report questionnaire correctly, to ensure that respondents had adequate cognitive functioning. To maintain confidentiality, the sampling and distribution of questionnaires was undertaken by Multiple Sclerosis Society of Queensland delegates under the instructions of the researcher. Procedures All participants completed a piloted, self-administered questionnaire booklet containing questions about their demographic and clinical characteristics, validated measures of quality of life and MS-related disability and a question on whether they had experienced clinically significant pain in the previous 2 weeks. It took respondents approximately 1 hour to complete. Each questionnaire was accompanied by an introductory letter, study information sheet, and a self-addressed reply-paid envelope. Request for respondents' contact details including telephone number and home address were included in the questionnaire, along with a single question determining whether they would consent to a follow-up interview. To increase the response rate, a reminder letter was sent 2 weeks after the distribution of questionnaires. To identify a subgroup likely to have clinically significant pain, participants responded to the following question from the BPI18: “Throughout our lives, most of us have had pain from time to time (such as minor headaches, sprains, and toothaches). Have you had pain other than these everyday types of pain in the last two weeks?” Participants who answered this question affirmatively were then contacted and asked to complete an in-person, structured pain interview assessing pain characteristics (ie, intensity, quality, location, extent, duration), exacerbating and relieving factors, and pain management techniques used. We decided to administer the pain interviews face-to-face to enhance the accuracy of measurement because some instruments were designed to be applied by interview (eg, the MPQ19). In addition, this method was chosen to prevent missing data and to allow for clarification of responses. The researcher negotiated, by telephone, a suitable time for the pain interview to take place. Most interviews were administered at the respondents' residences, although in 4 cases the interview took place at another mutually agreed location. The pain interview was administered in all cases by the primary researcher in a structured interview format guided by the use of selected instruments. It focused on pain experienced in the 2 weeks preceding the interview in order to limit errors due to memory and cognitive impairments. Additionally and in contrast to some past investigations,3, 10, 15, 17 all types of self-reported pain were included (eg, headache) on the grounds that such painful experiences may be related to MS either as a direct biologic consequence or as a response to the stress of adapting to the disease. A4-sized show cards were developed for each instrument requiring the choice of multiple answers to aid in the accuracy of responses. Average time interval from questionnaire to follow-up pain interview was 2 weeks (range, 1–3wk). The interview lasted approximately 45 minutes. The study questionnaire and protocol were approved by the Queensland University of Technology Human Research Ethics Committee. Study Measures The questionnaire consisted of 18 pages and was divided into 3 principal sections including demographic items, perceived quality of life, clinical characteristics, and MS-related disability. Only the first and third sections were relevant to the purpose of this study and are discussed below. Demographics Demographic items elicited information about sex, age, marital status, highest educational attainment, ethnicity, total annual household income, employment status and hours of paid employment per week, and residential location. MS-related measures The GNDS20 is an MS-specific measure of disability that evaluates functioning across 12 domains including cognition, mood, vision, speech, swallowing, upper-limb function, mobility, bladder function, bowel function, fatigue, sexual function, and other problems. Each subscale is graded according to its severity and impact on the person from 0 (normal function) to 5 (total loss of function with maximal assistance required), which are then summed to give an overall disability score ranging between 0 (no disability) and 60 (maximum possible disability). The GNDS has shown high internal consistency and test-retest reliability,20, 21 and self-report scores have been shown to correlate with clinical neurologic examination using the EDSS.22 In the current sample, the internal consistency of the GNDS was acceptable (α=.77). Two additional items assessed respondents' clinical course or type of MS, and time since their MS diagnosis. Pain Measures The follow-up pain interview included several standardized pain measures described below. Pain intensity An 11-point NRS (0 [no pain] to 10 [pain as bad as it could be]) from the BPI was used to assess pain intensity levels at present, worst, least, and on average over the previous 2 weeks. Each participant was read standardized instructions for the 11-point NRS developed by Wilkie.23 The reliability and validity of NRSs of pain intensity is well documented.24, 25 Pain quality The MPQ26 measures the sensory, affective, and evaluative aspects of the pain experience, based on the gate-control theory. The psychometric properties of the MPQ have been well established27, 28 and the MPQ is often used as a criterion standard against which to validate pain measures. It consists of 78 pain descriptors, which are categorized into 20 groups evaluating the major dimensions of pain quality. Participants were read each list of descriptors and could select 1 word from each group if applicable to their pain. To prevent measurement error due to MS-related memory or recall problems, A4-sized show cards were created for each group of words. Each of the 78 words are assigned a rank value within its group and from these data it is possible to derive a PRI for the sensory, affective, evaluative, and miscellaneous subscales, as well as a total PRI.26 Pain location and extent To measure the sensory distribution of pain, participants also completed a pain drawing with outlines of the human body, front and back, on which to shade in their pain site(s). The pain drawing was enlarged (height, 16cm) to fit a single A4 page. Margolis et al29, 30 have developed a scoring system where the drawing is divided into 45 areas, each with a corresponding percentage value in order to compute the total body area percentage in pain. This technique was applied using a clear plastic template to score percentage values. The test-retest and interrater reliability of data from these pain drawings have been established.29, 30 Other pain-related variables Along with other components of the pain interview, data were collected from each participant about the time since onset of MS-related pain, exacerbating and relieving pain factors, and current pain management techniques used. Data were transcribed verbatim in list format and later divided into conceptual categories for analysis. Statistical Analyses Data analysis was undertaken by means of the SPSS.a There was generally minimal missing data (<5% at the item level) across all measures, except for items concerning sexual activity in the GNDS where it reached 12%. Exploration of the pattern of missing data revealed that respondents and nonrespondents did not differ in terms of background characteristics. Because of the low incidence of missing data, we used sample mean substitution for subsequent analyses. Descriptive statistics (means, SDs, ranges, frequency counts, percentages) were calculated to profile sample characteristics and to determine pain prevalence and characteristics. At the bivariate level, we used contingency chi-square tests, independent t tests and Pearson product-moment correlations to evaluate the associations among illness and demographic variables and pain measures. Stepwise multiple logistic regression and multiple linear regression analyses were then undertaken to determine the most parsimonious set of variables that predicted the presence and absence of pain and pain intensity, respectively. For all analyses, an α level of less than .05 (2-tailed) was considered statistically significant. Results Response Rate Of the 500 postal questionnaires, 30 were returned due to incorrect addresses, 7 addressees were deceased, and a further 7 reported that they did not meet the eligibility criteria. Of the 456 questionnaires distributed, 219 were returned giving an overall response rate of 48%. Information on nonrespondents was not available because the researcher, in order to maintain participant confidentiality, did not have access to the mailing list. Sample Characteristics The demographic characteristics of the sample are summarized in table 1. With a mean age ± SD of 51.1±12.0 years (range, 24–82y), respondents were predominantly Anglo-Australian women who were married, well educated, and living in an urban area. Approximately two thirds of the sample indicated that they were not in paid employment at the time of the investigation. Participants who were employed reported a median of 25 hours of work per week (range, 3–55h/wk). Almost half of the sample (46.6%) reported an annual household income of up to AUD $25,000 per annum, which approximates the second lowest quintile of household income in Australia.31 Table 2 presents the clinical characteristics of the sample. The median time since MS diagnosis was 9 years (range, 0.5–60.0y). Approximately half of the sample described a relapsing-remitting disease course. Respondents' GNDS scores reflected a range of severity of MS-related disability within the sample, with an overall mean score ± SD of 18.5±9.4 (range, 0–48). The mean number ± SD of MS-related symptoms reported on the GNDS was 7.2±2.7 (range, 0–12) with respondents being most affected by fatigue, bladder dysfunction, mobility, and sexual problems. Speech, swallowing, and visual disability, in comparison, were reported to be relatively minor. In the last subscale (ie, other problems), 62.1% of the sample identified a problem not previously addressed by the scale. Of these, the most frequent was spasticity (39%), followed by sensory symptoms (ie, numbness, paresthesias) (33%), and dizziness and vertigo (28%). | | |  | Characteristics | n | % | |
|---|
| Disease course | | | | |  Relapsing-remitting | 106 | 48.4 | | | Secondary-progressive | 36 | 16.4 | | | Primary-progressive | 46 | 21.0 | | | Other | 31 | 14.2 | | | GNDS | Mean ± SD | | | | Cognition | 1.3±1.1 | | | | Mood | 1.3±1.3 | | | | Vision | 0.8±0.7 | | | | Speech | 0.5±0.9 | | | | Swallowing | 0.6±1.1 | | | | Upper limb function | 1.5±1.4 | | | | Lower limb function | 2.2±1.7 | | | | Bladder function | 2.5±1.8 | | | | Bowel function | 1.3±1.5 | | | | Fatigue | 2.7±1.6 | | | | Sexual function⁎ | 2.0±2.1 | | | | Other | 1.8±1.7 | | | | | |
What is the Prevalence and Nature of Pain Experienced by People With MS? Of the 219 respondents, 147 reported clinically significant pain during the 2 weeks preceding the study yielding a point prevalence of 67.1% (95% CI, 60.9%–73.3%). Of those reporting pain, complete pain interview data were available for 105 respondents. Reasons for respondents not being administered the pain interview included: no or incorrect contact details given (n=2); respondents now lived greater than 2 hours drive from Brisbane Central Business District (n=3); respondents were unavailable or not able to be contacted (n=20); or they did not consent to the pain interview (as indicated on the questionnaire (n=17). The following descriptive data are based on this subsample of 105 respondents reporting a current pain problem. When compared across background characteristics, participants who completed the pain interview were similar to those lost to follow-up except for age, with respondents slightly older (mean ± SD, 52.3±11.3y) compared with nonrespondents (mean, 48.1±11.4y) (t139=2.1, P=.037). Participants reported a mean pain intensity on average of 4.6±2.1 (range, 0–10) for the 2 weeks preceding the interview. Mean scores of pain “right now” and “pain at its least” were reported as 3.1±2.5 (range, 0–10) and 1.8±2.0 (range, 0–8), respectively. Mean pain intensity “at its worst” was 7.4±2.1 (range, 2–10). Table 3 shows the distribution of pain intensity scores when grouped by cutpoints representing mild (1–4), moderate (5–6), and severe (7–10) pain, following the work of Serlin et al.32 Notably, although 41.9% of participants rated their average pain intensity as mild, the majority reported a typical background pain of moderate (37.1%) to severe (18.1%) intensity. Approximately two thirds of the sample reported their pain intensity “at its worst” to be in the severe range. | | | | Pain Intensity Scores | Mild (NRS 1–4) | Moderate (NRS 5–6) | Severe (NRS 7–10) | |
|---|
| Presentpain | 46.7 | 21.0 | 10.5 | | | Worstpain | 10.5 | 21.9 | 67.6 | | | Leastpain | 46.7 | 10.5 | 1.9 | | | Averagepain | 41.9 | 37.1 | 18.1 | | | | |
The descriptive data derived from the MPQ are shown in table 4. MS-related pain was predominantly sensory-discriminative in quality, the most frequently endorsed descriptors (chosen by >33% of respondents) being sharp (54.3%), shooting (49.5%), cramping (45.7%), burning (43.8%), aching (42.9%), throbbing (39%), and tingling (38.1%). Affective and evaluative descriptors most frequently chosen were exhausting (59%), annoying (45.7%), and nagging (53.3%). In addition to these descriptors, study participants often supplemented the MPQ with analogies or metaphors to describe the quality of their pain. Common examples reported by participants included feeling as if they had “severe sunburn under a cold shower,” or as if their “legs were on fire.” | | | | Variable | Mean ± SD | Possible Range | Actual Range | |
|---|
| PRI total | 30.67±11.43 | 0–78 | 6–64 | | | PRI sensory | 19.10±6.96 | 0–42 | 4–35 | | | PRI affective | 4.14±2.98 | 0–14 | 0–11 | | | PRI evaluative | 2.26±1.43 | 0–5 | 0–5 | | | PRI miscellaneous | 5.17±3.10 | 0–17 | 0–14 | | | No. of words chosen | 12.74±3.96 | 0–20 | 4–20 | | | | |
In terms of the 45 anatomic areas defined by the scoring template of the Margolis pain drawing, the median number of painful locations reported by the sample was 10 (range, 1–43). The median percentage of body surface area in pain reported by the sample was 26.5% (range, 4.0%–96.5%). Pain locations were also scored according to a broader categorization of body regions similar to classifications used by others in the MS-related pain literature5 (table 5). Based on this classification, three quarters of the sample reported pain in 3 or more locations, with respondents reporting an average of 4.0±1.8 distinct pain sites. Total number of pain sites were found to be significantly associated with overall MS-related disability score (r=.28, P=.006). Although the median duration of pain for the sample was 6 years (range, 1mo–36y), for a substantial minority (34.3%) pain had persisted for over 10 years. The majority of participants (68%) reported that they experienced pain on a constant, daily basis and most of the remainder (24.5%) described their pain as intermittent. | | | | Location | Frequency | % | |
|---|
| Head | 23 | 21.9 | | | Back | 71 | 67.6 | | | Neck | 40 | 38.1 | | | Face | 36 | 34.3 | | | Arms | 35 | 33.3 | | | Hands | 39 | 37.1 | | | Trunk | 26 | 24.8 | | | Legs | 90 | 85.7 | | | Feet | 57 | 54.3 | | | | |
Respondents were also able to identify a number of factors known to provoke or exacerbate their pain. Table 6 reports the percentage of respondents reporting each factor. Participants most commonly stated that prolonged activity or overexertion made their pain worse. Changes in environmental temperature, bodily posture and position, stress, fatigue, and sensory stimulation were also reported to exacerbate pain. The data on pain management techniques used by the sample are summarized in table 7. The mean number ± SD of pain management techniques reported by participants was 3.3±1.7 (range, 0–8). When compared by background characteristics, women reported more pain management techniques than men (mean, 3.5±1.6 vs 2.4±2.1; t103=2.4, P=.017), as did participants in paid employment compared with those not in current paid employment (mean, 4.1±1.8 vs 2.9±1.6; t103=3.3, P=.001). Number of reported techniques did not significantly differ by other characteristics. Most participants (83.8%) took medications regularly for pain relief, although these were predominantly over-the-counter simple analgesics, such as nonopioids and NSAIDs. Participants used a range of other nondrug pain management techniques including physical and/or exercise therapy, thermotherapy, rest and/or sleep, distraction, relaxation techniques, as well as a range of alternative and complementary therapies. | | | | Factors | Frequency | % | |
|---|
| Activity or exercise | 49 | 46.7 | | | Environmental temperature | 37 | 35.2 | | | Postural (eg, immobility, certain movements) | 33 | 31.4 | | | Stress | 26 | 24.8 | | | Fatigue | 20 | 19.0 | | | Sensory stimulation (eg, light touch, friction) | 9 | 8.6 | | | | |
| | | | Techniques | Frequency | % | |
|---|
| Medications | | | | | Nonopioid analgesics | 65 | 61.9 | | | Anti-inflammatories | 30 | 28.6 | | | Spasmolytics | 22 | 21.0 | | | Antidepressants | 19 | 18.1 | | | Opioids | 15 | 14.3 | | | Anticonvulsants | 11 | 10.5 | | | Alternative medicines | 9 | 8.6 | | | Disease-modifying agents | 8 | 7.6 | | | Other treatments | | | | | Physical or exercise therapy (eg, massage, physiotherapy) | 55 | 52.4 | | | Thermotherapy (eg, hot or cold) | 36 | 34.3 | | | Rest or sleep | 29 | 27.6 | | | Distraction (eg, work, recreation) | 21 | 20.0 | | | Relaxation techniques (eg, meditation, guided imagery) | 16 | 15.2 | | | Alternative therapies (eg, acupuncture, aromatherapy, hypnosis, magnetic therapy) | 13 | 12.4 | | | | |
What Illness and Demographic Variables Are Associated With the Presence and Intensity of MS-Related Pain? To determine whether pain prevalence differed by illness and demographic characteristics, comparisons between participants with and without MS-related pain were first conducted at the bivariate level. Location was omitted given the low cell count in suburban and rural categories. These analyses did not reveal any significant associations between the presence of pain and age, marital status, educational level, ethnicity, socioeconomic, or employment status (table 8). In addition, although there was a notably higher proportion of women (69.3%) reporting pain compared with men (57.5%), this difference fell short of statistical significance (χ2=1.6, P=.21). In terms of illness-related variables, no significant differences existed between the 2 groups with regard to disease course or time since MS diagnosis. However, the presence of pain was associated with more severe MS-related disability with a mean difference of 6 score units on the GNDS (95% CI, 3.5–8.4; t217=−4.8, P<.001). When pain prevalence was considered by GNDS class intervals, the report of pain became more common with increasing level of disability (χ2=27, P<.001) (fig 1). | | | | Variable | With Pain (n=147) | Without Pain (n=72) | χ2/t | P⁎ | |
|---|
| Sex, n (%) | | | 1.6 | .21 | | | Male | 23(57.5) | 17(42.5) | | | | | Female | 124(69.3) | 55(30.7) | | | | | Marital status, n(%) | | | 2.3 | .31 | | | Single | 28(60.9) | 18(39.1) | | | | | Married or de facto relationship | 96(70.6) | 40(29.4) | | | | | Separated/widowed | 21(60.0) | 14(40.0) | | | | | Educational level, n(%) | | | 2.2 | .70 | | | <High school graduate | 14(63.6) | 8(36.4) | | | | | High school graduate | 76(70.4) | 32(29.6) | | | | | Apprenticeship | 12(66.7) | 6(33.3) | | | | | University or college | 35(66.0) | 18(34.0) | | | | | Postgraduate | 9(52.9) | 8(47.1) | | | | | Ethnicity, n(%) | | | 0.0 | .90 | | | Anglo-Australian | 138(67.3) | 67(32.7) | | | | | Other | 8(61.5) | 5(38.5) | | | | | Annual household income(AUD$), n(%) | | | 4.6 | .20 | | | <10,000 | 16(61.5) | 10(38.5) | | | | | 10,000–24,999 | 49(76.6) | 15(23.4) | | | | | 25,000–49,999 | 37(67.3) | 18(32.7) | | | | | >50,000 | 28(58.3) | 20(41.7) | | | | | Employment status, n(%) | | | 0.5 | .49 | | | Paid employment | 46(63.0) | 27(37.0) | | | | | Not in paid employment | 99(68.8) | 45(31.2) | | | | | MS type, n(%) | | | 4.2 | .12 | | | Relapsing-remitting | 76(71.7) | 30(28.3) | | | | | Secondary-progressive | 31(86.1) | 5(13.9) | | | | | Primary-progressive | 38(82.6) | 8(17.4) | | | | | Mean age ± SD (y) | 51.3±11.5 | 50.6±13.2 | 0.4 | .69 | | | Mean time since MS diagnosis ± SD (y) | 11.2±9.7 | 12.4±10.3 | −0.9 | .38 | | | Mean disability ± SD (GNDS) | 20.4±8.7 | 14.4±8.5 | 4.8 | <.001 | | | | |
| ⁎ P calculated using chi-square tests, except for age, time since diagnosis, and disability, for which independent t tests were used. |
A stepwise multiple logistic regression was subsequently conducted to examine the independent associations of illness and demographic characteristics with the presence of clinically significant pain. All demographic variables were entered, along with time since diagnosis and MS type. In addition, as MS-related disability was significant at the bivariate level, all 12 GNDS scales were entered to identify important associations with specific disability scales. As shown in table 9, the final model fit the data well (Hosmer-Lemeshow goodness-of-fit test, χ2=4.86, P=.77). When considered together, 4 of the background variables were significantly related to the likelihood of having clinically significant pain, namely sex, cognition, sexual function, and other problems (as indicated on the GNDS, eg, spasms, vertigo, paresthesias). Being female increased participants' likelihood of experiencing MS-related pain more than 3-fold relative to males (OR=3.40; Wald χ2=6.69, P=.01). In addition, each unit change on the cognition (Wald χ2=4.25, P=.039), sexual function (Wald χ2=8.61, P=.003), and other (Wald χ2=20.07, P<.001) scales of the GNDS increased participants' likelihood of pain 1.4, 1.3, and 1.9 times, respectively. To examine associations between illness and demographic characteristics and pain intensity among respondents reporting a current pain problem, we used a stepwise multiple linear regression analysis. All illness-related and demographic variables were entered as independent variables, with pain intensity as measured by the MPQ PRI total as the dependent variable. As shown in table 10, the final model, which accounted for 27% of the variation, included disability, sex, marital status, and time since diagnosis. Greater severity of MS-related disability (t=4.31, P<.001) and female sex (t=2.47, P=.015) were significantly associated with higher levels of pain intensity, whereas being in a married or in a de facto relationship (t=−2.28, P=.025) and longer time since MS diagnosis (t=−2.24, P=.028) correlated with lower pain ratings. | | | | Predictor Variables | b | SE b | β | sr2 | |
|---|
| Disability (GNDS) | 0.47 | 0.11 | .40† | .16 | | | Female | 6.71 | 2.71 | .23⁎ | .05 | | | Married or de facto relationship | −5.08 | 2.23 | −.21⁎ | .04 | | | Time since diagnosis | −0.23 | 0.10 | −.21⁎ | .04 | | | Constant | 20.13† | | | | | | | |
Discussion In this large, community-based sample of people with MS, clinically significant pain was experienced by 67.1% of participants during the 2 weeks preceding the survey. This finding is consistent with a growing consensus in the literature that pain is experienced by approximately two thirds of the MS population over the course of their illness5, 6, 7, 8, 17 and reaffirms that pain is a significant problem among people with MS. Others have found considerably lower,3, 11, 13, 14 or higher,4, 12, 33 prevalence rates, which likely reflect differences in sampling procedures, measurement and classification systems used, or timeframes and exclusion criteria for MS-related pain. Indeed, several inconsistencies and methodologic limitations within the extant MS-related pain literature have generally precluded substantive conclusions about the prevalence and nature of pain experienced. Notably, almost all available data is based on convenience samples drawn from specialized clinics or hospital departments, thereby limiting the generalizability of findings. This study therefore sought to overcome many of these limitations by using (1) community-based, systematic random sampling; (2) comprehensive, in-person structured pain interviews; (3) standardized pain measures; and (4) the inclusion of all self-reported pain problems within 2 weeks preceding the survey, so as to include clinically meaningful pain while avoiding information bias due to memory problems. Although the current study attempted to correct a number of methodologic limitations of previous prevalence studies, the findings may have been influenced by a number of factors. Despite efforts to emphasize study participation regardless of pain status, the results may reflect some degree of selection bias. That is, respondents with pain may have been more or less likely to complete the questionnaire than those without and therefore be over- or under-represented in this sample. Moreover, because the sample was restricted to members of the Queensland Multiple Sclerosis Society, the sample may have been biased toward persons with differing characteristics, such as people with greater access to resources. Nonetheless, the background characteristics of the sample were quite representative of the target population and other published epidemiologic data. The high prevalence of pain experienced in the MS population raises the question of why some people do not develop pain over the course of the disease. It could prove informative to determine what demographic, clinical, and psychosocial factors protect against the development of chronic pain problems. Compatible with previous studies, the current study found the presence of MS-related pain to be unrelated to several important demographic and clinical variables including age, marital status, educational level, ethnicity, socioeconomic and employment status, disease course, or time since diagnosis. Pain, however, correlated significantly with level of disability, as measured by the GNDS. This suggests that pain may be more likely among those with greater disease severity, although this relationship remains unclear from these cross-sectional results. When considered independently by logistic regression, cognition, sexual function, and other scales of the GNDS were significantly associated with the presence of pain. It may be that people with greater cognitive impairment are more likely to experience ongoing pain due to impaired cognitive coping and problem-solving abilities. On the other hand, both cognitive34, 35 and sexual36, 37 difficulties are common among persons with chronic pain as a primary condition. MS-related pain may itself create memory and concentration difficulties and interfere with sexual interest and functioning. Further investigation is needed to determine the nature of these relationships. The only study to examine the relationship between pain and cognitive functioning in MS found no differences in performance on a task of auditory verbal learning between those with and without pain.17 The finding that the other GNDS variable was significantly associated with pain must be qualified by the fact that it commonly included potentially painful conditions such as spasms and paresthesias. Hence, this finding may simply indicate that as participants developed more MS-related symptoms that may be painful, they are more likely to develop pain. Few consistent findings about clinical characteristics associated with pain have emerged from previous research. Several studies failed to identify any relationship between MS-related pain and indices of disease progression, such as disease course, duration, or severity.5, 6, 7, 8, 9, 10 In contrast, Brochet et al11 prospectively assessed 108 people with MS over a 3-year period and found that pain occurred more frequently during acute relapses and pain persisted more frequently when exacerbations were followed by residual neurologic deficit. These authors reported a significant correlation between pain and increased disability, as measured by the Kurtzke Disability Status Scale. Stenager et al12 also showed that over a 5-year period, participants with deteriorating Disability Status Scale scores were significantly more likely to experience pain. Recent large, cross-sectional studies by Ehde,13 Solaro,14 and colleagues also found pain prevalence increased with greater disease severity, as defined by the EDSS. Here, logistic regression also revealed that being female independently increased participants' probability of experiencing MS-related pain more than 3-fold (OR=3.40; 95% CI, 1.4–8.6). This finding is compatible with previous studies8, 15, 16 showing that women were significantly more likely to report MS-related pain than men. It is also consistent with increasing evidence that several chronic pain problems appear to have a specific sex distribution. Women appear to be at greater risk of a variety of recurrent and chronic pain conditions such as headache, facial pain, abdominal pain, and musculoskeletal pain.38, 39 Both biologic and psychosocial factors have been hypothesized to account for these findings, such as sex differences in social role expectancies, cognitive appraisals, coping strategies, familial factors, anatomic structures, hormones, and brain chemistry.38, 40 It should be noted, however, that the current sample predominantly included women, yielding a female-to-male ratio of approximately 4:1, which does not correspond with the 2 to 3:1 sex ratio typical of the MS population.41 An important finding in this study was that pain in people with MS is not only common, but it is also usually chronic and often severe in nature. At the time of investigation, the median duration of pain was 6 years, but for a significant minority (34.3%), pain had existed for over 10 years. Of those participants with pain, 68% reported that they experienced pain on a constant, daily basis. Most of the remainder (24.5%) also experienced pain on a daily basis, although it was described as intermittent. Thus, once MS-related pain develops, it is usually a chronic, persistent problem over the course of the illness. Participants reported a mean pain intensity ± SD on average of 4.6±2.1 (on a 0–10 scale) for the 2 weeks preceding the interview, which is similar to that reported by other authors. Four studies4, 8, 9, 13 found average pain intensity among people with MS to range from 4.6 to 5.8 using the NRS. Further examination of the data, however, reveals that over half (55.2%) of the current sample reported a typical background pain of moderate-to-severe intensity (≥5 on a 0–10 scale). In addition, approximately two thirds (67.6%) of the sample reported their pain intensity at its worst over the preceding fortnight to be in the severe range. These findings replicate those of Ehde et al,13 who reported that average pain intensity was often moderate (35.6%) to severe (26.7%) for their community-based MS sample over the 3 months preceding their survey, as measured by the 11-point NRS. Findings from the MPQ further show that the severity of MS-related pain is considerable. The mean total PRI ± SD for the sample was 30.67±11.43, exceeding calculated normative PRI total mean scores reported by Wilkie et al27 for chronic cancer (24), low back (27.9), and mixed (25.4) pain conditions. Participants' mean scores were also appreciably higher when compared with means reported for Australian samples of chronic rheumatoid arthritis,42 orofacial pain,43 and chronic postsurgical pain.44 The qualitative aspects of pain reported by this sample are similar to those found in the MS literature.6, 8, 45 Interestingly, participants scored comparatively lower on the affective and evaluative dimensions of the MPQ. One possible explanation for this finding is that pain is less distressing or threatening to people in the context of other intrusive MS-related symptoms. Or as is suggested by previous qualitative findings,46 people may come to accept pain as a permanent consequence of disability, one that becomes an enduring part of daily life. Thus they might tend to perceive and discuss pain primarily in terms of its sensory qualities rather than its affective-evaluative dimensions. Descriptive findings from the MPQ were also remarkably similar to those of Dudgeon et al47 who explored the qualitative features of disability-related pain among people with lower-limb amputations, spinal cord injury, and cerebral palsy, using both the MPQ and open-ended pain interviews. The authors found word pattern use to be similar across groups and therefore suggested a set of 15 adjectives, derived from the most frequent descriptors, to inform disability-related pain assessment. These adjectives correspond well with the current findings and may have clinical utility in the MS population. Like Dudgeon,47 however, we also found that during pain interviews study participants often supplemented the MPQ with analogies or metaphors to describe the quality of their pain. Some participants described a sensation similar to severe sunburn under a cold shower, or as if their legs were on fire, or explained their whole body ached with fatigue. Such descriptions likely represent the often-frustrated attempts of those with central pain to convey their subjective experience48 and perhaps point to a limitation of measures such as the MPQ to adequately assess the complex nature of chronic disability-related pain.47 Little is known about what factors influence pain intensity among people with MS. A correlational study by Brunet et al49 found higher income and relapsing-remitting MS predicted lower pain levels, whereas a family history of MS and the presence of headaches were associated with higher pain severity, as measured by the 36-Item Short-Form Health Survey bodily pain scale. Other investigators, however, have found no association between pain severity and age, disease duration, MS subtype, or EDSS scores.4, 7, 9, 50 In the current study, regression analysis revealed that women and participants with greater disease severity reported significantly higher levels of pain, whereas being in a married or in a de facto relationship and longer time since diagnosis predicted lower pain scores on the MPQ. The finding that women reported greater pain severity is consistent with 3 previous studies in the MS literature,8, 16, 50 as well as evidence from other pain-related conditions such as rheumatoid arthritis or osteoarthritis,51, 52 human immunodeficiency virus or acquired immune deficiency syndrome,53 and neuromuscular disease,54 suggesting that women who have chronically painful conditions are likely to report heightened pain compared with men. Overall MS-related disability score showed the strongest association with pain intensity, which stands in contrast to previous findings.7, 9, 50 However, because several pain variables in this study were correlated with disease severity, the conclusion that pain is related to advanced disease seems warranted. Being in a partnered relationship was associated with significantly lower pain intensity, suggesting that social support may be an important buffer against the development of severe pain problems.55, 56 Longer time since MS diagnosis also predicted lower pain intensity, which may reflect increased attempts to use self-management strategies and greater adaptation to illness over time.57 Taken together, these findings suggest that in contrast to a biomedical model of disability-related pain that ties pain severity solely to disease activity and impairment, a range of factors likely interact to influence the severity of MS-related pain. It is noteworthy that the majority of study participants reported multiple pain locations, experiencing several types of pain simultaneously. When scored across 9 bodily regions, participants reported a mean ± SD of 4.0±1.8 different pain sites. Three quarters of the sample reported pain in 3 or more locations. Participants most commonly described pain in the lower extremities, although pain was frequently reported in the back, neck, upper extremities, and facial regions also. The number of painful regions and localization of pain as found in this study are very similar to those found by others.6, 8, 14 Archibald et al9 found that 89% of subjects with MS-related pain had multiple anatomically separate pain sites, reporting a mean of 4.1 pain locations. The present data also show that number of pain locations was positively correlated with MS-related disability. Although previous studies have failed to examine this relationship, a compounded effect of multiple areas of pain on functioning seems likely. Thus, it may be important to consider more than simply the presence or severity of pain when examining the relationship between pain and MS-related disability. Moreover, given that people with MS typically experience multiple pain problems, additional studies are needed to determine the causes of these conditions and whether there are common patterns of multiple pain problems in this population. The pain variables assessed in the current study focused on the overall subjective experience of MS-related pain. However, given the diverse nature of MS-related pain, it may be useful for future research to clinically differentiate between pain conditions and perform detailed analyses by pain type, because each may have varying intensity and functional consequences.58 Participants were able to identify a number of factors that were known to provoke or exacerbate their pain. The most common triggers were prolonged activity or overexertion, changes in environmental temperatures or bodily posture or position. Others noted that stress, fatigue, and sensory stimulation aggravated pain. In addition, participants reported a variety of treatments and strategies they used to alleviate pain. Most participants (83.8%) took medications regularly for pain, although these were predominantly nonprescription, simple analgesics such as nonopioids (eg, paracetamol and aspirin products) and NSAIDs (eg, ibuprofen). Although anecdotally ineffectual, most study participants self-medicated with simple analgesic preparations and therefore health care providers should be aware of the extent of over-the-counter medication use when new drug therapies are initiated. Approximately less than one fifth of participants who reported pain were being treated with opioid or adjuvant pharmacotherapy. Several nonpharmacologic pain management strategies, including physical therapy, thermotherapy, rest and sleep, distraction, relaxation techniques, and alternative therapies were also used by participants. It is unknown whether these strategies were initiated by study participants or whether health care professionals recommended them. However, given the number and diversity of therapies spontaneously reported, future research should examine the effectiveness and comparative effectiveness of these strategies so that clinicians can base recommendation and treatment on empirical evidence. Study participants reported an average of 3.3±1.7 current pain management techniques, with greater numbers of techniques being reported by women and those in paid employment. Heckman-Stone and Stone4 similarly found women with MS reported more pain management strategies than men, citing higher health care use among women and a greater willingness to try nonmedication strategies as potential explanations. Women may also be more motivated to try pain-relieving techniques because they reported greater pain intensity. Similarly, people may attempt to cope with MS-related pain by using a variety of self-management strategies to remain employed. Further inquiry into the effectiveness of pain management techniques used by people with MS in the community and potential barriers to self-management should be the target of future research. Conclusions Consistent with previous research, pain was found to be common among people with MS, with 67.1% of this community-based sample reporting pain during the 2 weeks preceding the study. Comprehensive pain assessment revealed that a substantial subset of these subjects experience chronic pain conditions characterized by moderate to severe pain intensity. Moreover, study participants reported an average of 4 concurrent pain sites. These findings underscore the need for increased clinical focus on assessment and management of MS-related pain. In contrast to previous cross-sectional studies, greater severity of MS-related disability strongly correlated with both pain prevalence and severity. Greater disability was also associated with multiple pain locations. Taken together, these results suggest that people with more severe MS are at a greater risk for developing clinically significant pain. This explanation seems biologically plausible, yet one that remains confounded by the correlational research design. Longitudinal research is required that examines how MS-related disability and pain covary over time. The findings also show significant sex differences, because women were independently associated with both increased prevalence and severity of MS-related pain. Women also reported greater extent of pain compared with men and used a greater number of self-management strategies. Thus, women with MS may be at particular risk for developing pain problems. 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a School of Nursing, Queensland University of Technology, Kelvin Grove, QLD, Australia b School of Nursing and Midwifery, Griffith University, Meadowbrook, QLD, Australia  Reprint requests to Clint Douglas, RN, PhD, School of Nursing, Queensland University of Technology, Victoria Park Rd, Kelvin Grove, QLD, Australia 4059
Supported by the Multiple Sclerosis Society of Australia. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. PII: S0003-9993(08)00504-2 doi:10.1016/j.apmr.2008.03.022 © 2008 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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