It is now recognized that most people with cerebral palsy (CP) enjoy a life expectancy similar to that of the general population (1). This opens new perspectives for understanding of the impact of childhood disability on young adults. Quality of life (QoL) has been considered a key concept in disability research for the past two decades (2). However, its conceptual definition and its measurement in people with disabilities or chronic conditions are complex and still debated in the literature (3). In short, while health-related QoL (HRQoL) refers to those aspects of life that are directly influenced by disability, health problems, or treatments (4, 5), QoL is viewed as a broader concept that is not limited to functioning but encompasses subjective well-being and life satisfaction (6) in line with the approach proposed by the World Health Organization (WHO). Thus, QoL is a multidimensional construct defined as “the individual's perception of his or her position in life in the context of the culture and value system in which he or she lives, and in relation to his or her goals, expectations, norms, and concerns” (7).

Two points deserve particular attention when exploring trajectories of QoL from childhood to adulthood in people with childhood-onset disabilities. First, QoL explores subjective well-being across a range of domains that vary in relevance over time, necessitating the use of age-appropriate instruments. Second, because QoL measurement is weighted by the respondent's internal norms and values, having functional limitations does not systematically mean poor QoL for a given individual (6, 8). Previous studies have nonetheless shown that people with disabilities or chronic conditions report lower QoL scores as a group than the general population. However, the difference varies in magnitude depending on the context, suggesting that these differences may be more related to personal and environmental factors (personal resources, mental health, social support, and socioeconomic status) than to disability (9).

There has been little research on QoL in young adults with CP and even less on change in QoL from childhood. From studies carried out in children and adolescents, we know that pain is a factor strongly associated with a reduced QoL and that severity of impairment and associated conditions also negatively influence QoL (10–15). Deterioration in mobility, high rates of pain, and mental health problems have been observed in young adults with CP (16–20) and justify study of the impact of functional deterioration on QoL in a changing context for these persons who have new expectations and concerns (such as living independently or having romantic and intimate relationships). In addition, from a clinical perspective, it would be interesting to better understand the impact of disability on change in QoL across the life span and to identify what early factors, if any, can limit the deterioration of QoL. To the best of our knowledge, only one Dutch study (21) has explored QoL trajectories from childhood to transition to adulthood in individuals with CP, but it had several limitations. One of these was that it did not include young adults with intellectual disabilities. Overall, it is a major limitation of the existing literature that individuals with the most severe phenotypes are often excluded, notably because of their inability to self-report their QoL. Many authors have raised concerns about proxy-patient reporting, such as its lack of reliability and accuracy, particularly when exploring social or emotional domains (22–24). This leads to a poor representation of this population in studies.

The SPARCLE study aims to document the impact of personal and environmental factors on QoL, with the explicit goal of allowing all individuals with CP to contribute regardless of their severity profile. In this analysis, using longitudinal data from the European SPARCLE cohort, we sought to identify how the QoL of individuals with CP evolves from childhood to young adulthood and whether the severity of impairment and frequency of pain and seizures affect their QoL. We also aimed to determine whether different shapes of QoL trajectories exist in order to better understand the impact of impairment and comorbidities on QoL.

Our longitudinal sample included 164 young adults with CP (40.8% of eligible subjects) of whom more than two-thirds self-reported (with or without assistance) to the SPARCLE 3 questionnaire (n = 111, 67.7%). A total of 130 subjects participated in all the waves of the SPARCLE cohort with a similar self-report rate (n = 89, 68.5%).

In this longitudinal analysis of the SPARCLE cohort, we observed that QoL in individuals with CP linearly decreased from childhood to young adulthood in the domain of psychological well-being, whereas it linearly increased in social relationships. Severity of impairment was associated with reduced QoL in all life phases studied (childhood, adolescence, and young adulthood): motor impairment with social relationships, and intellectual impairment with psychological well-being and social relationships. At all time periods, frequent pain reduced psychological well-being, and seizures were associated with poorer QoL in the social relationships domain. Using clustering methods, we identified a group of young adults with CP who presented a reverse pattern to the overall trajectory of QoL in both domains.

To our knowledge, our study is the first to investigate long-term trajectories of QoL in young people with CP from childhood to early adulthood using individual longitudinal data. A Dutch study by Tal et al. also investigated long-term trajectories of QoL dimensions related to psychological and social functioning but reconstituted a longitudinal sequence with four neighboring 4-year follow-up cohorts: toddlers (n = 97), children (n = 116), adolescents (n = 108), and young adults (n = 103) (21). Unlike our findings, QoL in the domains of psychological and social functioning did not change significantly over time. Apart from study design, a series of differences between the two studies may explain the divergent results. Whereas, Tal et al. considered aspects of life directly influenced by disability, health problems, or treatments (4, 5), we used a broader definition of subjective QoL that encompassed the concept of holistic well-being (6). Although QoL and HRQoL reflect the individual's subjective perception of their position in life (30), these outcomes are substantially different (34, 35). In addition, the sample used by Tan et al., consisting of individuals with CP recruited from rehabilitation centers, had less severe impairment than those in our study and did not include young adults with intellectual disabilities. However, our results relating to long-term trajectories of QoL were unchanged when we excluded from analysis young adults with intellectual disabilities or those with proxy reports (94% with intellectual disability, 60% with GMFCS IV–V). Interestingly, we demonstrated that change in QoL with age was not one-directional. Our clustering analysis showed that 26.2 and 12.3% of the study population displayed a reverse trajectory of QoL in the psychological well-being and social relationships domains, respectively, as compared with their peers. Inclusion in these groups did not appear to be related to a specific profile of disability severity. The proportion of proxy reports did not significantly differ between these particular groups and the other two groups. Nevertheless, because of the small size of the groups, we were not able to investigate whether these reverse QoL trajectories were determined by specific factors. In young adults with CP, the association between severity of motor impairment and QoL appears to depend on the domain considered. Three cross-sectional studies investigated the association between GMFCS levels and psychological well-being (17, 36, 37) and reported conflicting results. Although they all used the concept of HRQoL, two studies showed no significant difference in perceived mental health across the range of GMFCS levels (36, 37), in agreement with our findings, whereas one study (17) showed that young adults with the most severe gross motor function impairments (GMFCS III–V) were more likely to have better perceived mental health than those less severely impaired (GMFCS I–II). On the other hand, our findings suggesting that severe motor impairment may affect the subjective perception of social relationships during childhood, adolescence, and young adulthood are not consistent with the findings of Tan et al. (21). While analysis of the SPARCLE data collected in childhood and adolescence identified GMFCS as a factor associated with QoL in the social relationships domain (14), it is interesting to note that fine motor function appears to have a more determining role for social interaction in young adults with CP. However, this association disappeared when individuals who proxy-reported their QoL were excluded (sensitivity analyses). The interpretation of these latter results is difficult. First, they may point to a specific social condition of individuals with the most severe profiles. Second, we cannot exclude that our findings may be supported by under- or overestimation of QoL in the social relationships domain due to proxy responses. Individuals reporting on behalf of another person often have a substantially different perspective on the QoL domain under consideration (23). To our knowledge, identification of intellectual impairment and seizures as factors associated with lower QoL in the social relationships domain from childhood to young adulthood has never previously been reported in the literature. Interestingly, these associated factors have previously been identified as determinants of non-inclusion at school (38), whereas severe intellectual impairment and seizures have also been reported as factors associated with unemployment (39–42). Because a recent qualitative study has highlighted the relationship between social participation and QoL (43), it is possible that the factors associated with lower QoL in the social relationships domain identified in this study indirectly reflect limited access to education or employment or, more generally, restrictions on social participation. Given that pain has been shown to be strongly associated with reduced psychological QoL in childhood and adolescence (12–14), it was not surprising to observe that this association continued in young adulthood. This finding confirms the importance of addressing pain across the life span in people with CP, especially as the prevalence of frequent pain is high regardless of age (44–49). In addition, fatigue frequently co-occurring with pain (48, 50) should be considered in further analyses of the role of pain. Our models for QoL in the psychological well-being and social relationships domains explained 16 and 18%, respectively, of the variance in outcome, which may seem low. However, this is not surprising because from childhood to early adulthood, people with CP face numerous and complex barriers that can impact QoL, and these barriers are not limited to the severity of impairment and the presence and frequency of pain (51–53). The SPARCLE cohort is, to the best of our knowledge, the largest prospective study of people with CP from childhood to young adulthood. Our sample was selected from European population-based registries or various sources in northwest Germany, thus limiting selection bias. We purposely overrepresented the most severe forms of CP to investigate this less common group in depth. However, our choice calls into question the external validity of our findings, notably for QoL trajectories. Moreover, we cannot exclude that dropouts during follow-up led to the exclusion of the most severe cases. All analyses were adjusted for the predictors of non-response identified in this study to limit the impact of dropout. Despite these potential differential errors, it is interesting to note that the participants in the SPARCLE cohort who contributed to the third wave had a similar distribution of impairment and seizures when they were children as the individuals born between 1990 and 2006 and recorded by the SCPE (54).

No instrument has been developed to adequately measure QoL over such a wide age range. Therefore, we used two different instruments based on the same concept and the WHO definition (7). As mentioned earlier, these two instruments presented the advantage of having a comparable number of items and response modalities, and of providing QoL scores on a 0–100 scale. Nevertheless, we cannot be sure that this choice is valid for bridging the age gap between adolescence and young adulthood. First, it is likely that the two instruments have different Rasch scaling. Therefore, it would have been better to use transformed Rasch scores that take into account discriminant ability of items rather than raw scores as we did. However, we were limited by the lack of data on the psychometric properties and population norms of the WHOQOL-Bref in our specific population of European young adults, whereas Rasch scores exist for the KIDSCREEN-52 and were constructed to meet the population norms of European children and adolescents (mean = 50, SD = 10) (29). We considered additional analyses to explore this point, but none seemed satisfactory. Among them, use of the KIDSCREEN index, a short form of the KIDSCREEN-52, which was collected in all waves of this study, was considered; but unfortunately, this instrument only measures overall QoL and not domain-specific QoL. The exact opposite is true for the WHOQOL-Bref. This limited our ability to use the KIDSCREEN index as a validation tool in our study. Finally, we performed the analyses by pooling self-reports and proxy reports to describe QoL across the whole range of severity of our population, considering that regardless of the respondent, the report was the best available estimate of QoL. We cannot rule out a potential for under- or overestimation of QoL when using proxy reports (23). But the majority of our findings did not change when proxy reports were excluded from our sensitivity analyses, reducing the impact of this limitation. Only the association between BFMF and QoL in the social relationships domain was no longer significant, which may nuance our findings in this particular domain. Furthermore, given that the majority of individuals with intellectual disability (IQ <70) was in the proxy-reporting group (n = 50/85, 58.9%) while almost all of those with an IQ ≥ 70 were able to answer the questionnaire themselves (n = 75/77, 97.4%), the significant impact of intellectual disability on QoL trajectories observed in the total sample was no longer significant when the analyses were restricted to self-reports.

Identification of QoL trajectories and their associated factors improves our knowledge of the experience of individuals with CP up till young adulthood. Further studies are needed to better understand which of the disability, personal, and contextual factors have the most influence on the differently shaped long-term trajectories of QoL.

The data analyzed in this study is subject to the following licenses/restrictions: dataset is accessible after submission of a scientific project and approval of the project by the investigators of each participating country. Requests to access these datasets should be directed to Catherine Arnaud, catherine.arnaud@univ-tlse3.fr.

The relevant Ethics and Regulatory authorizations were sought in each country and the study fully approved by the below: France: The data were collected and stored in accordance with the reference methodology MR003 [Declaration No. 2205849 at the Commission for Data Protection and Liberties (CNIL)] each patient having been informed individually of the research under Article L1122-1 of the Public Health Code. Germany: Ethikkommission der Universität zu Lübeck [AZ 18-172]. Italy: Comitato Etico Lazio 1c/o A.O. San Camillo Forlanini [2143/CE Lazio 1]. Sweden: Regional Ethical Review Board in Göteborg. All young people with CP or their legal representatives gave written informed consent to participate, or non-opposition where appropriate.

NVEB and CA conceived and designed the analysis. NV performed the analysis under the supervision of VE and drafted the manuscript. CA, JF, SS-S, UT, KH, and MM conceived and designed the cohort and contributed to the longitudinal data. CA, CD, SS-S, UT, KH, and MM designed the third wave of follow-up, which was managed by CD. All authors contributed to the article, provided critical feedback, and approved the submitted version.

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) and the French Agence Nationale de la Recherche (ANR) (DFG-ANR N°316684170) in Germany and France; the Sunnerdahls Handikappfond, the Swedish state under the agreement between Swedish government and the country councils, the ALF-agreement (ALFGBG-726001) in Sweden; and the Fondazione Carivit in Italy. The funders were not involved in any way in the preparation of this manuscript or the decision to submit it.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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