INTRODUCTION
Cerebral palsy (CP) describes a group of permanent disorders of the development of movement and posture, causing activity limitations that are attributed to nonprogressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of CP are often accompanied by disturbances of sensation, perception, cognition, communication, and behavior; by epilepsy; and by secondary musculoskeletal problems.1(p. 9)
CP is the most common cause of physical disability in childhood, occurring in 2 to 2.5 per thousand live births.2 Although the pathophysiology of CP is nonprogressive, the clinical manifestation of the condition is not. Adults with CP have high rates of secondary conditions that evolve over the lifespan and affect function and quality of life.3 Secondary conditions are not a part of the primary disabling condition but occur as a result of the condition; as such, they are viewed as potentially preventable.4 In 2 review articles relating to secondary conditions associated with CP, both Campbell4 and Gajdoski et al5 identified pain as one of the most common secondary impairments.
Pain is also a major topic of concern for children with CP and their families. In a qualitative study to develop a condition-specific measure of quality of life for children with CP, Waters et al6 determined that 1 of 13 themes deemed to be associated with quality of life was “body pain and discomfort.” Specifically, a high quality of life was perceived to be associated with the absence of stiffness and soreness in joints. In a study of a large and representative sample of children aged 8 to 12 years with CP living in 6 European countries, pain was experienced by more than half of the respondents in the previous week.7 Children who reported pain had significantly lower quality of life in the following domains: physical well-being, moods and emotions, self-perception, autonomy, relationships with parents, and school environment. Accordingly, these authors recommended that children's pain should be carefully assessed and managed. Others recommend obtaining the perspectives of children and youth, as well as their parents, in evaluating pain and its effect on daily life.8
Pain is clearly important to the everyday experiences of children, youth, and adults with CP, especially if the pain is chronic.9 We now explore what is known about the prevalence, location, intensity, and the effect of pain on daily lives of adults and children with CP.
Adults with CP
Chronic pain is a common secondary impairment in adults with CP, with prevalence rates ranging from 67% to 84% depending on the sample.10–12 The progression of secondary impairments in adults with CP is a concern as it has been reported that a third of this population deteriorates in function from adolescence to adulthood.13 Fifty percent to 69% reported pain in more than 1 body location,13–15 with the back and lower extremity being most often reported.13 Pain is also variable,15 with pain frequently being reported in the back, neck, foot, and ankle,16,17 and pain has been found to be influenced by the severity of CP.17 Although individuals with CP are reported to cope with aspects of pain, pain has also been found to be associated with low life satisfaction (45% of sample), deteriorating physical function,17 and poorer quality of life and physical and mental functioning.18
Forty percent of adults reported moderate to severe intensity of body pain,16 and pain intensity was found not to change during a 2-year period.17 Responses from 221 adults with CP to a mailed questionnaire14 indicated that 18% reported experiencing pain every day, and only a small fraction (21%) reported never experiencing pain. The remaining participants reported occasional pain.
Although in other studies, as many as 49% of adults reported no interference in their daily activities as a result of the pain they experience,14 pain intensity was found to account for 44% of the variance in predicting pain interference.16 In a non–population-based sample, in which approximately 21% of participants reported mild, moderate, or severe pain, there was no correlation with the Barthel index.19
Children and Youth with CP
The literature suggests that children with CP score very differently in domains of pain on the Child Health Questionnaire when compared with children without CP.20,21 Prevalence studies reported rates ranging from 61% to as high as 78% depending on the sample.22–25 Although the potential inflation of these rates because of convenience sampling is a concern, the rates have been supported in population-based studies, in which parents have reported rates as high as 53.6% for moderate pain and 18.1% for severe pain.26 Pain frequency has also been reported, with parents indicating rates of 11%27 and 36%24 of children experiencing pain daily and reports of 35% to 52% weekly.23,24 Pain intensity is not often reported, but a mean intensity of 6.1 on a 10-point scale has been found in a non–population-based sample of children with CP.23 Moreover, it was found that girls reported more extreme pain22 regardless of motor impairment,27 although this finding has not been supported elsewhere.23
Few studies have reported how pain characteristics are affected by the severity of CP (most frequently measured using the Gross Motor Function Classification System [GMFCS]),28 and those that have are inconsistent. A greater proportion of children who were ambulatory reported pain compared with children who were not ambulatory, although no significant trends were found across GMFCS levels.22 A similar lack of relationship between GMFCS level and pain was reported by Kennes et al.29 In contrast, other authors have suggested that pain is correlated with functioning level or motor impairment.27,30 Breau et al23 found that children who had greater motor abilities experienced more accidental pain. Recently, pain prevalence by GMFCS level was reported for a sample of children with a mean age of 11 years,31 with no significant differences among classifications.
Pain has also been correlated with poor quality of life among children.7,26 Interference with daily activities was associated with those activities related to mobility and high physical demand.24 Parental report suggested that 33% of children experienced pain interfering with normal activities. In a phenomenological study by Castle et al,9 the experience of pain in a sample of adolescents highlights its overwhelming effect on their lives.
Purpose
Although the pain experiences of adults with CP are relatively well understood, the corresponding literature relating to children and youth is limited. Children and youth with CP have been reported to experience pain, yet the nature of it is still not well understood. Little research exists on understanding how pain is affected by GMFCS level and gender; moreover, no work has been done to date that investigates location of pain in this younger population. In addition, the literature is dominated by parental reports of pain, with few self-reports from the perspective of the person who has CP. The purpose of this article is to describe pain in a population-based sample of youth with CP, with a focus on pain distribution, intensity, and effect on daily activities across gender, and GMFCS levels.
METHODS
Design
The data reported here were obtained from the first data collection point of a prospective cohort study called the Adolescent Study of Quality of Life, Mobility and Exercise (ASQME).
Setting and Participants
The ASQME is a 5-year follow-up of the 5-year long Ontario Motor Growth (OMG) study32 that followed a stratified random sample of 567 children with CP from a population-based cohort obtained between 1996 and 2001. In brief, for the OMG study, participants were recruited through 19 publicly funded children's rehabilitation centers in the province of Ontario. Because each program serves the majority of eligible children in its geographical area, this sample is proposed to be closely representative of the population of children with CP in Ontario. The OMG sample was stratified by the GMFCS level28,33 and age and is not necessarily representative with respect to those factors.
All 343 OMG participants who were 11 years or older in April 2002 were invited to participate in ASQME. A total of 244 (71.1%) youth and families agreed to participate, and 230 of these completed a pain questionnaire at the first of 4 scheduled annual data collection points. Participants of ASQME were not significantly different from eligible OMG study participants who chose not to participate on all background variables except for maternal education; nonparticipating eligible individuals had mothers with lower education levels than ASQME participants. Otherwise, we propose that the participants of this study are as close to population based as possible. Overall, the sample comprised 104 females and 126 males with mean ages of 14.7 and 14.8 years (SD for both = 1.7 years) at the study onset. Table 1 contains the distribution of gender, age, Spinal Alignment and Range of Motion Measure34 scores, and health utilities index attribute scores for cognition35 by GMFCS level. As expected, the cognitive utilities decrease and the Spinal Alignment and Range of Motion Measure scores increase from GMFCS levels I to V. The ASQME study was approved by the Research Ethics Board at McMaster University. Written informed consent was obtained from caregivers, and written assent was obtained from the adolescent participants.
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TABLE 1: Descriptions of Participants by Gender and GMFCS Level
Measures
Although many measures were used in the ASQME study, only 2 are relevant here: the GMFCS and the Pain Questionnaire. The GMFCS28 is a standardized, reliable, and valid system to classify motor function of children with CP aged 2 to 12 years of age. As part of the work of the ASQME study, a version for youth aged 12 to 18 years was validated.36 Using this system, classification is based on each individual's self-initiated movement and need for assistive technology and wheeled mobility. Individuals are classified into 1 of 5 levels, from I, in which the person is able to walk and run but is limited in more advanced skills, to V, in which the person has very limited mobility. This classification system is quick and easy to use by anyone who is familiar with the motor abilities of persons with CP.
A pain questionnaire was developed by our team for the purpose of this study. Participants were asked to respond to the initial question “Over the past month, have you experienced physical pain?” (yes or no). Those responding “yes” were asked “Please indicate how severe your pain was over the past month, on average,” with response options from 1 (very little pain) to 10 (extremely painful). They were also asked to indicate “How much the pain gets in the way of your daily activities over the past month” from a low of 1 (does not get in the way at all) to 10 (unable to carry out activities because of the pain). Finally, they were asked to indicate the body regions in which they experienced pain. The pain questionnaire is included in the Appendix, which is available online at https://links.lww.com/PPT/A6.
Procedures
Trained and reliable physical therapists classified ASQME participants using the GMFCS. Adolescents provided data on pain either independently or through proxy by parental report. There was no difference in the proportion of the sample reporting pain or the magnitude of the severity of pain or the effect on daily activities between the adolescents who completed the questionnaire either independently or with physical help from parents, and those who required parents to respond on their behalf because of their cognitive limitations.
Statistical Analyses
Frequency distributions were used to describe the prevalence of pain and its presence in various body regions. Chi-square analysis determined the differences in frequency of pain by gender and GMFCS level. Medians and ranges were used to describe the intensity of pain. Spearman ñ was used to determine the relationship between intensity of pain and effect on daily activities.
RESULTS
Overall, pain was reported by 63% of females and 49% of males (Fig 1). Pain prevalence was highest in GMFCS level II for males and GMFCS level V for females. Slight variations did exist among GMFCS levels, although no visible trend was found for increasing GMFCS levels, an effect that was found to be nonsignificant after a χ2 analysis. Females generally reported more pain than males for all levels, except GMFCS level I. No statistically significant effect was found between genders.
Fig. 1.:
Prevalence of pain in adolescents with CP across GMFCS levels and gender.
Figure 2 contains bar graphs representing the proportion of the sample reporting pain across body regions by GMFCS and gender. Adolescents (both males and females) in GMFCS level I reported pain in the ankle and foot (n = 25), knee (n = 14), calf (n = 14), and lower back (n = 11). A similar trend was observed in GMFCS level II, with the ankle and foot (n = 17), knee area (n = 11), and lower back (n = 7) being most often reported. The results from GMFCS level III displayed a similar degree of variation, with the majority reporting pain in the ankle and foot (n = 20), knee (n = 10), lower back (n = 10), hip (n = 9), and neck (n = 8). Adolescents in GMFCS level IV demonstrated higher proportions of reported pain across more body regions, as the results from the ankle and foot (n = 20), thigh (n = 15), hip (n = 14), knee area (n = 13), shoulder (n = 13), and lower back (n = 13) reports demonstrate. Patterns in GMFCS level V are very different. The ankle and foot (n = 15) and knee (n = 11) areas were most often reported. Unlike the other 4 levels, the upper back was reported more often (n = 5) compared with the lower back region (n = 2). In addition to analyzing reports by GMFCS levels, results were also analyzed by gender. Males in GMFCS levels I and IV reported pain in more regions compared with females, whereas females reported experiencing pain in more regions for levels II, and slightly more for levels III and V. Overall, the knee and ankle/foot regions represent key areas in which the adolescents experienced pain, regardless of GMFCS level. In addition, the lower back seems to be a highly reported painful area, for those classified in levels I to IV.
Fig. 2.:
Percentage of males and females in GMFCS levels who reported pain in specific body regions. n indicates neck; Sh, shoulder; E/F, elbow and forearm; W/H, wrist and hand; H, hip; Th, thigh; Kn, knee; Ca, calf; A/F, ankle and foot; BN, back of neck; UB, upper back; LB, lower back.
Of the 65 females and 63 males who reported pain (Fig 1), the median intensity of pain reported ranged from a median of 3 to 5 for both genders across GMFCS levels (Fig 3). For females, level IV had the highest median report of pain (5.0), and males reported the highest intensity of pain in levels IV and V (5.0 for both). There is little difference in the reports of pain intensity across GMFCS levels, and the reports of intensity ranged across the entire spectrum of possible values. Only GMFCS level III for females and GMFCS level II for males displayed a small range (1–5) of pain values. The largest range was observed at level III for males (1–10) and levels IV and V for females (1–10 for both).
Fig. 3.:
Intensity of pain across GMFCS levels among those who reported pain in males and females.
Figure 4 highlights the effect of pain on daily activities for GMFCS levels and gender. The medians of the effect of pain demonstrated a small range, from values of 2.5 to 4.0 across GMFCS levels. The lowest median for females was in GMFCS level III (2.5) and males in GMFCS level II (2.5). The highest effect was for level IV for females (median of 3.5), and levels III, IV, and V for males (median of 4.0 for all; refer to Fig 4). No trends were found for GMFCS level and effect of intensity on daily activities, although a significant relationship was found between intensity of pain and degree to which pain interfered with daily activities. A correlation of 0.75 for females (n = 65) and 0.82 for males (n = 63) was determined (p < 0.01, 2-tailed).
Fig. 4.:
Reported effect of pain on daily activities for GMFCS levels and gender.
DISCUSSION
This study is the first to use a population-based sample to investigate the prevalence of pain, localization of painful regions, intensity, and its effect on the daily activities of adolescents with CP. Although no statistically significant differences were found across GMFCS levels or between males and females, the results do highlight some interesting trends that support previous work done with adults and children, despite a potential limitation with recall bias in the period of a month before responding.
Prevalence
The prevalence of pain in our sample, 62.5% and 49.2% for females and males, respectively, is similar to results reported by Dickenson et al,7 with rates of 54% for participants in a population-based sample in Europe of children aged 8 to 12 years. Moreover, GMFCS level was not found to be associated with the prevalence of pain, a result that has been reported in the literature pertaining to both children7,29,31 and adults.13 This suggests that children in each level require equal attention in terms of working toward alleviating pain. Gender and GMFCS level do not significantly influence the experience of pain, although females report more pain for all GMFCS levels except for level I, which supports earlier work showing that males were perceived to have less pain than females.22,27 Research with adults has shown significant associations between pain and gender,17 suggesting the possibility that earlier trends become stronger. Given this, it is important to pay close attention to the pain experience of females, and also, to clarify whether females are more likely to report pain than males, an effect which is likely to bias self-reporting results. This self-reporting bias can have important implications in planning interventions and providing appropriate care for both males and females.
Body Regions Involved
Studies concerning body regions implicated in the pain experience are very limited in this young population and work conducted to date with adults supports the results of this study. One study conducted by Castle et al9 with adolescents locates pain in the hips, back, bladder, and upper limbs, although this effect is not classified by level of involvement. In adults, the body regions most often implicated with pain are those of the lower extremities and back,11,12,17 findings that are similar to those reported here. Although no significant differences were found across GMFCS levels and between genders and the reporting of pain, there are differences between genders observable as trends that have the potential to direct intervention and the efficient provision of services. Given that this is the first study conducted concerning the location of pain in a sample of adolescents, it is important to replicate these results in other samples and to conduct more investigations looking at differences across GMFCS levels. The similarities between these data and those from adults suggest that these pain experiences start early and continue into adulthood, and early intervention has the potential to alleviate some of these experiences.
Intensity of Pain
The intensity of pain was not found to differ significantly between males and females, and further, no differences were found across GMFCS levels. The intensity of pain was rather consistent across levels, with higher medians for those in levels IV and V. Earlier work by Breau et al23 highlights that children with less motor abilities reported more nonaccidental pain, which was also found to be associated with higher mean intensity of pain, compared with those with greater motor abilities who reported more accidental pain and a lower mean intensity of pain. Other authors who studied populations of children report relationships between severity of pain and motor impairment,27 and still there is some debate.29 More work needs to be conducted investigating the role of GMFCS and motor involvement in pain. Nonetheless, our results suggest that alleviation of pain is an important factor for individuals at all levels and should be an important factor when planning interventions, given the frequency and intensity of pain in adulthood.11,24
Activities of Daily Living and Quality of Life
We reported here that the experience of pain significantly affects daily activities. Tervo et al22 reported that 33% of parents reported that their child's pain interfered with normal activities. Quality of life and participation are important components of health, and earlier work indicates that pain is associated with low life satisfaction7,26 and deteriorating physical function in children,30 adolescents,13 and adults.17 Pain has been associated with poorer quality of life in children.7,26 The experience of pain has been associated with negative educational and social consequences in children,27 as well as aspects of self-care and sleep.24 Greatest functional interference has been found with aspects of mobility,24 and a lack of physical activity has been documented to potentially contribute to the development of pain.37 These observations have important implications for alleviating pain and encouraging activity and participation in children and adolescents to manage future pain experiences.
Children have reported a greater effect of pain than adults, which might be reflected by differences in perception or more effective learned coping strategies. Work with adults highlighted only minor interferences with activities,11,12,14 although pain was found to have an influence on lifestyle decisions.15 Coping strategies have been found to be associated with pain interference and depressive symptoms.16 Interventions directed toward coping and pain management might account for differences in reports in adults. Pain has been shown to mediate the relationship between diagnostic subtypes of CP and school functioning,8 highlighting the importance of focusing on pain and pain management in interventions for children. More work needs to be done investigating potential shifts in perception—an effect that is difficult to capture through parental reports that are common in the literature pertaining to children. Self-reports are important for capturing the effect of pain from the perspective of the individual with the disability. Moreover, Gajdosik et al5 suggested that individuals with CP need to monitor at least 3 different components of their overall health: acute health problems (eg, infections), lifestyle health risks (eg, heart disease), and secondary impairments associated with their condition (eg, pain and musculoskeletal health).
The results of this study highlight the prevalence, location, intensity, and effect of pain in children and youth with CP and draw attention to a need to focus on the prevention of secondary impairments, with an emphasis on health promotion. To provide the evidence for this recommendation, future work should be conducted to better understand the contributions of the patella alta, hip subluxation/dislocation, and scoliosis and other malalignments and past bone surgeries on pain experiences. Moreover, other work should focus on understanding appropriate types and amounts of physical activity for different musculoskeletal conditions manifested by children and youth with CP. With this knowledge, children and youth can be encouraged to take responsibility for their musculoskeletal health and physical fitness,4 with the potential to develop lifelong healthy habits that continue through adolescence into adulthood. Improving clinical practice to account for these needs is possible through the development of appropriate programs focused on lifelong fitness, weight control, musculoskeletal health, education about the nature of disability, self-management, and self-determination.4 Both Campbell4 and Gajdosik et al5 emphasized that therapists need to take a greater role in educating children and families about the lifespan issues and the clinical course of CP. Given that pain is so prevalent among individuals with CP, it has been suggested that the preadolescent years are an appropriate starting point for increasing awareness about pain.5
CONCLUSIONS
Ultimately, developing a better understanding of the effect of pain on the activities of daily living, school functioning, participation, and exercise in children and youth can assist with developing effective programs directed toward early health promotion and ultimately increasing integration and quality of life. The prevention of the development of chronic pain is an important goal, and combining self-determination with the prevention of musculoskeletal impairment can provide long-term benefits that persist well into adulthood.
ACKNOWLEDGMENTS
The authors thank the ASQME (Adolescent Study of Quality of Life, Mobility and Exercise) study team (Peter Rosenbaum, Robert Palisano, Steven Hanna, Dianne Russell, Stephen Walter, and Barb Galuppi) for their support and access to the data.
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