ReviewTowards a better understanding of MS pain: A systematic review of potentially modifiable psychosocial factors
Introduction
Pain affects around two thirds of people with Multiple Sclerosis (MS)1 [1] and is associated with poor quality of life [2], [3], [4]. Prevalence rates for pain in MS are reported to range from 40 to 80% [2], [5], [6]. This variability may be explained by the divergent definitions of pain used and patient populations studied [5]. A third of people with MS describe pain as one of their worst symptoms [7]. People with MS may experience acute or chronic pain [8] arising from multiple aetiologies [9] including neuropathic pain resulting from injury to nerve tissue, musculoskeletal pain related to degenerative muscle or joint dysfunction and migraine headache [5], which can be neuropathic in origin or secondary to the disease process [10], [11]. Neuropathic pain includes extremity pain, trigeminal neuralgia, Lhermitte's sign and painful tonic spasms including paroxysms. People with MS can experience one or more of these pain syndromes across their disease course [12], [13], but prevalence does not appear to be associated with age, disease duration [14] or MS subtype [15], [16].
MS pain is typically treated within a biomedical framework. However, a recent review suggests that biomedical treatments achieve only modest reductions in pain severity [17] and a large proportion of people with MS experience ongoing uncontrolled pain [18]. Pain in MS may benefit from a broader conceptualisation including psychosocial factors that may contribute to the experience of pain and incorporating these in treatment approaches. There is at least one proposed biopsychosocial theory of pain-related interference for MS [14], [18]. Although an important advance, it draws from a more general model of stress rather than a model or theory developed specifically from empirical data on pain in MS. One way to expand this formulation may be to draw not only on the empirical MS pain literature, but also on the extensive theoretical and empirical literature on primary, non-disease related, chronic pain [19].
The primary chronic pain literature distinguishes between two key outcomes of pain, the severity of the pain and physical dysfunction, including the extent to which pain interferes with activities of daily living, relationships with others and sleep [20]. These outcomes are considered separately because pain severity only explains some of the variance in the extent to which pain interferes with physical functioning. Physical functioning can also improve even in the absence of improvements in pain severity [21], [22]. Several potentially modifiable cognitive, emotional, behavioural and social factors or processes consistently explain variance in physical functioning over and above pain severity in this group [23].
A range of theoretical models exist which attempt to explain how these modifiable psychosocial factors interact to maintain the severity of pain and impact of pain on physical function (pain interference). Early operant behavioural theory [24] highlighted the negative impact of environmental influences (e.g. overly solicitous responses to pain by others) on pain behaviours and outcome. The traditional cognitive behavioural model [25] expanded on operant behavioural theory, suggesting that pain-related emotions, beliefs and coping responses (e.g. anxiety, low mood, self-efficacy and perceived social support) also play a crucial role alongside behaviour. Pain catastrophizing, defined as an exaggerated negative orientation towards painful stimuli during actual or anticipated pain experience [26], also emerged as a key component of the traditional cognitive–behavioural model [27], and a consistent predictor of outcome. Recent expansions to the traditional cognitive–behavioural model include two specific behavioural pathways: The fear-avoidance model [28] suggests that pain-related fear, defined as interpreting potentially pain-inducing situations as threatening and causing further damage to the body, contributes to hypervigilance, behavioural avoidance and inactivity, resulting in greater pain and interference [29], [30]. A recent addition to this model suggests another opposing pathway, avoidance–endurance [31], characterised by suppression of pain and increased task persistence, leading to physical overuse and overload, greater anxiety, depression and ultimately reduced functioning.
More recently, contextual cognitive–behavioural theory [32] or acceptance and mindfulness-based ‘third-wave’ approaches have been applied to chronic pain [33]. Influenced by operant behavioural theory and the traditional cognitive–behavioural model, these draw on six integrated processes within the psychological flexibility model [34]. One process, pain acceptance, defined as willing engagement in activities in a way that includes contact with pain, without defense or attempts to struggle with or control it [35], [36], has consistently been identified as a key process of change influencing reductions in pain severity and interference [37], [38]. Although there is no single unifying model of pain, most have reasonable empirical support [39], [40], [41], [42]. There is also a large body of evidence suggesting that therapies based on these theoretical approaches decrease pain severity, disability and related mood disturbance in primary, non-disease-related chronic pain conditions [39], [41].
Whilst primary chronic pain may have a different pathophysiology to pain secondary to a neurological condition, exploring psychosocial factors drawn for these models in the context of MS pain will provide insight as to any overlap in these conditions.
The purpose of this study is therefore to identify and systematically review evidence for potentially modifiable psychosocial factors associated with pain severity and pain interference in the MS literature, applying quality ratings when evaluating and interpreting study findings. We refer to pain interference specifically rather than the broader construct of physical functioning as in the context of MS, the latter is potentially effected by a wide range of disease-related symptoms. How these data relate to existing theories of primary chronic pain will be explored and a working theoretical framework of MS pain proposed. Finally, this review will provide directions for future research in this area with a view to refining a psychological treatment approach to pain in MS.
Section snippets
Criteria for including studies within the review
Studies were included if they met both the following two criteria: (a) Studies of adults with MS experiencing pain and (b) used quantitative, psychometrically validated pain severity and pain interference measures in conjunction with cognitive, emotional, behavioural or social factors/processes typically considered modifiable in the context of cognitive–behavioural models of pain and treatment. Studies were also required to either: (c) Explore bivariate relationships between psychosocial
Study characteristics
The combined search yielded 5012 abstracts, after removing duplicates. Thirty-one studies (29 published and 2 unpublished) were identified as meeting the inclusion criteria for this review (Fig. 1) and are summarised in Table 1. Table 2 summarizes the strength of psychosocial factors examined in relation to pain severity and interference measures across these studies. Supplementary materials: Appendix D provides a full summary of the key methodological, demographic and clinical characteristics
Perceived social support and perceived solicitude
Within the broader psychological literature [49] and primary chronic pain models (e.g. operant behavioural [24] and traditional cognitive-behavioural model [25]) perceived social support and perceived solicitude have been conceptualized as both helpful and unhelpful psychosocial factors [50], [51]. Solicitous responding is typically defined as a primary reinforcing process by the spouse associated with unhelpful pain behaviours in primary chronic pain conditions [24]. Perceived solicitousness
Pain acceptance
One medium quality study (M. Glowacka, unpublished data, June, 2010) demonstrated a large negative relationship between the pain willingness component of the Chronic Pain Acceptance Questionnaire (CPAQ) and pain interference at the bivariate level.
Summary of regression findings
A number of cross-sectional studies identified associations between pain severity, interference and psychosocial variables using multivariate models. Other than perceived social support and solicitude [9], [67], [74], all psychosocial predictors within regression models, usually in conjunction with other psychosocial factors, were significant, accounting for between 4 and 30% of the variance in pain severity and pain interference [9], [53], [57], [66] (M. Glowacka, unpublished data, June, 2010:
Overall completeness and applicability of the evidence
The purpose of this systematic review was to identify and assess the quality of studies looking at potentially modifiable psychosocial factors associated with MS pain severity and interference and synthesise the evidence. 31 studies, most of medium to good quality, offer preliminary support for the presence of several treatment modifiable psychosocial factors related to MS pain.
In most instances, in line with the primary chronic pain literature [23], correlations between a range of psychosocial
Conflict of interest
The authors report no conflicts of interest. This review is supported by the Multiple Sclerosis Society (Grant number: 967/12).
Acknowledgments
The authors express thanks to the MS Society for funding this research.
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