The study of the descriptive epidemiology of chronic widespread pain (CWP) in several countries is of interest, as the occurrence of this condition varies among different populations. However, reports of pain prevalence are not consensual: it is clear that chronic musculoskeletal pain is frequent all over the world, varying from 4.2% to 13.3%. The reasons for the prevalence differences in CWP might include genetic and/or environmental factors.
Multifactorial aetiopathogenesis of CWP and fibromyalgia syndrome (FMS) certainly includes genetic susceptibility and environmental influences. The risk factors for the occurrence and maintenance of CWP/FMS include female gender, increasing age, family history of chronic pain, several causes of distress, obesity and poorest mental and/or physical status. On the other hand, risk factors that negatively influence the outcome of CWP/FMS are: high levels of psychological distress, presence of somatisation, presence of fatigue, poor sleep, higher number of painful sites and pain intensity, poorest mental status and functional capacity, presence of co-morbid conditions and highest number of primary-care consultations. Mild alcohol consumption and individualised social support seem to have a protective effect on the outcome of CWP/FMS.
Descriptive epidemiology
Introduction
Chronic widespread pain (CWP) and fibromyalgia syndrome (FMS), from a rheumatological perspective, are viewed as generalised musculoskeletal pain syndromes. From the broader epidemiological perspective of chronic pain, there is accumulating evidence that multiple chronic musculoskeletal pain sites, irrespective of formal definitions of ‘widespreadedness’, are an important measure of the population burden of pain and pain-related disability . This represents a shift towards thinking of multiple-site chronic pain as a continuum of experience, often established early in adult life, and away from the categorical view of widespread pain. To paraphrase Croft , the question is “How much of it have you got?” rather than “Have you got it?”. A large Norwegian cohort study tracked the number of musculoskeletal pain sites in participants over a 14-year period from 1990 to 2004 and found that the number of sites reported was stable over time (68.8% of those who reported five or more sites at baseline reported the same number of sites 14 years later) . Furthermore, this was seen consistently across age groups, suggesting that the persistence of relatively stable multi-site musculoskeletal pain is established early in adult life. From the perspective of measuring and reducing the global burden of musculoskeletal pain, the number of pain sites, a continuous measure with strong prognostic capacity for pain-related disability, may prove to be suitable as a marker of individual and population risk analogous to blood pressure .
Intriguingly, recent developments in the conceptualisation of FMS show a similar line of thought, with a shift away from a category-based definition towards a continuum-based approach . Twenty years after the American College of Rheumatology (ACR) first published fibromyalgia classification criteria, new ACR preliminary diagnostic criteria have been developed .
The fundamental change in the new criteria is that they allow fibromyalgia to be characterised as part of a dynamic continuum of chronic widespread musculoskeletal pain that takes into account changes in the ‘widespreadedness’ of pain in a quantitative manner as well as taking into account changes in concomitant symptoms (e.g., fatigue and loss of restorative sleep) and their level of severity. With the removal of the sometimes controversial requirement for tender points as a diagnostic criterion , there is now the potential for wider use of the new criteria in surveys and in future rounds of estimating the global burden of disease.
With a better understanding of the important role of central pain processing in CWP and in FMS, the gaps between the ‘fibromyalgia literature’ and the ‘chronic pain literature’ are rapidly narrowing. However, this article is based on what has gone before, and so necessarily focusses on studies of CWP and FMS that have used the 1990 ACR criteria.
Case definition
For many common musculoskeletal conditions, there are significant variations in case definitions that have been used in epidemiological studies that estimate population burden. This is as true for commonly occurring conditions, such as low back pain, as it is for generalised musculoskeletal pain conditions.
Incidence versus prevalence: selecting the most appropriate measure
In epidemiological studies of disease occurrence, two commonly used measures are incidence (first-ever occurrence or onset of a condition) and prevalence (presence of a condition), which may be measured at one point of time, or over a defined period of time. Generalised musculoskeletal pain conditions are characterised by a gradual onset, are often established by early adult life and follow a complex episodic course with remittance and recurrence of pain symptoms. It is therefore debatable whether measures of incidence do, in fact, capture initial onset of the condition or the onset of a new episode of an already prevalent condition. Therefore, prevalence is the preferred measure in the context of generalised musculoskeletal pain conditions.
Morbidity
Generalised musculoskeletal pain syndromes are commonly associated with an array of symptoms and conditions. Some of these – pain at multiple sites, fatigue, sleep disturbance, mood disturbance and cognitive symptoms (e.g., impaired concentration and memory) – are also found in other musculoskeletal conditions and a range of syndromes characterised by the co-occurrence of multiple symptoms, such as chronic fatigue syndrome and irritable bowel syndrome . The new ACR diagnostic criteria for FMS incorporate specific measures of persistent common symptoms and symptom severity for fatigue, lack of restorative sleep, cognitive problems and somatic symptoms in general .
Generalised musculoskeletal pain syndromes can have a profound effect on health-related quality of life (HRQoL); compared with the general population, those with CWP or, particularly, FMS report lower scores on the Short-Form (36) Health Survey (SF-36) .
A notable feature of the effect of generalised musculoskeletal pain syndromes on HRQoL is the global impact on physical and psychological well-being and functioning, seen consistently across studies .
Mortality
CWP/FMS is associated with neuroendocrine disturbances, smoking, poor exercise capacity and increased body mass index. Therefore, there are a priori grounds for considering whether these conditions contribute to increased mortality. There are studies that have shown a statistically significant but small relationship between different forms of widespread pain and increased risk of cancer mortality ; however, others have not .
A new Danish study examined mortality in a cohort of FMS patients seeking care between 1984 and 1999 through linkage to the Danish Mortality Registry . While there was no overall increase in mortality, there was an elevated risk of cause-specific mortality in females for three causes of death: suicide (10-fold increase in mortality risk), liver cirrhosis/biliary tract disease (sixfold increase in mortality risk) and cerebrovascular disease (threefold increase in risk). Recently, a large prospective data linkage study found that, for chronic pain more generally, socio-demographic factors appeared to explain the relationship between pain and mortality . However, severe pain (defined by high levels of pain intensity and substantial pain-related disability) was associated with an increased risk of all-cause mortality even after adjusting for socio-demographic factors.
Geographical variation
Geographical differences in occurrence of chronic widespread pain
What is the importance of epidemiological studies of rheumatic diseases?
The study of the descriptive epidemiology of rheumatic diseases in several countries and areas around the world is of interest, as the occurrence of these diseases varies among different populations. Geographical, ethnic and racial factors can be determinant for their frequency and expression. In contrast to industrialised countries, the prevalence of rheumatic diseases in developing countries is largely unknown. The investigation of the epidemiological profile of rheumatic diseases in these countries can reveal the role of environmental and lifestyle factors characteristic of this populations, providing insights into the disease aetiology.
Why study CWP ‘and’ Fibromyalgia?
CWP is the cardinal symptom of the FMS, one of the most common reasons for referral to a rheumatologist.
Prior to 1990, several diagnostic criteria for FMS and CWP were available . In 1990, the ACR established the classification criteria for CWP , which is defined as pain above and below the waist, involving both sides of the body and lasting for at least 3 months, and for FMS, which includes CWP and the observation of pain brought on by pressure at specific anatomic sites. Previous studies did not use consistent criteria for this syndrome and, in particular, definitions of widespread pain differed. Therefore, we should not neglect the fact that minor differences in the definition of widespread pain can be reflected in the disease prevalence estimates .
Although CWP is the cardinal feature of FMS, the relation between these two clinical expressions of chronic pain is by no means clear. Neither CWP nor FMS appears as confined conditions, as with time, patients frequently move across different categories of pain syndromes . This supports the concept that chronic pain conditions may constitute a continuum of pain distribution from localised to widespread, rather than different entities. About 20% of the population with CWP also has 11 of 18 tender points , and in 70–80% of the patients who later develop FMS, the disease starts with localised and intermittent pain. The number of painful sites usually increases slowly over the years, before the patient finally develops the full-blown picture of FMS . It is not clear why some people with widespread pain also have a compatible FMS examination and others do not.
Very few studies have estimated the prevalence of CWP in the general population and there are currently no published robust international epidemiological data even though the classification criteria can be easily applied to an epidemiological context ( Table 1 ).
| Study | Year | Country | Age group | Prevalence (%) total | Prevalence (%) women |
|---|---|---|---|---|---|
| Forseth et al. | 1992 | Norway | 20–50 | NI | 15.3 |
| Croft et al. | 1993 | England | 18–79 | 11.2 | 15.6 |
| Wolfe et al. | 1995 | USA | 18+ | 10.6 | NI |
| Jacobsson et al. | 1996 | USA (Pima) | 35–70 | 0.0 | NI |
| Mikkelsson et al. | 1997 | Finland | Pre-adolescents | 7.5 | NI |
| White et al. | 1999 | Canada | 18+ | 7.3 | NI |
| Hunt et al. | 1999 | England | 18–65 | 4.7 | 5.3 |
| Buskila et al. | 2000 | Israel | 18+ | 9.9 | 14.0 |
| Lindell et al. | 2000 | Sweden | 20–74 | 4.2 | NI |
| Bergman et al. | 2001 | Sweden | 20–74 | 11.4 | NI |
| Storzhenko et al. | 2004 | Russia | 27–75 | 13.3 | NI |
| Mas et al. | 2008 | Spain | 20+ | 8 | NI |
Valuable information about the epidemiological aspects of CWP can be obtained by reviewing studies on FMS. FMS appears to have a worldwide distribution, particularly in the Western world, where differences in frequency can be found between various geographical regions ( Table 2 ).
| Study | Year | Country | Age group | Prevalence (%) total | Prevalence (%) women |
|---|---|---|---|---|---|
| Mäkelä and Heliövaara | 1991 | Finland | 30+ | 0.8 | 1.0 |
| Forseth and Gran | 1992 | Norway | 20–49 | NI | 8.6–10.5 a |
| Lydell and Meyers | 1992 | South Africa | 35+ | NI | 3.2 |
| Prescott et al. | 1993 | Denmark | 18–79 | 0.7 | 1.3 |
| Wolfe et al. | 1995 | USA | 18+ | 2.0 | 3.4 |
| Lindell et al. | 1996 | Sweden | 20–74 | 1.3 | NI |
| Farooqi and Gibson | 1998 | Pakistan | 15+ | 0.1–3.2 b | NI |
| Clark et al. | 1998 | Mexico | 9–15 | 1.2 | 2.5 |
| White et al. | 1999 | Canada | 18+ | 3.3 | 4.9 |
| Carmona et al. | 2001 | Spain | 20+ | 2.4 | 4.2 |
| Cardiel and Rojas-Serrano | 2002 | Mexico | 16+ | 1.4 | NI |
| White and Thompson | 2003 | Amish, Canada | 18+ | 7.3 | 10.4 |
| Senna et al. | 2004 | Brazil | 16+ | 2.5 | 3.89 |
| Haq et al. | 2005 | Bangladesh | 15+ | 3.2 b | NI |
| Salaffi et al. | 2005 | Italy | 18+ | 2.22 | NI |
a Minimum and maximum prevalences.
Reports of pain prevalence are not consensual, at least in part, as a consequence of the different definitions of pain used in individual studies, but also likely due to study methodologies and populations. Despite these facts, it is clear that musculoskeletal pain is frequent all over the world.
Prevalence of CWP and fibromyalgia
Recent studies have reported that CWP is common in the general population and its prevalence, varying between 4.2% and 13.3%, is quite high in the USA, UK, Canada, Israel and Russia ( Table 1 ). Population-based studies of CWP performed in the USA and UK suggest that approximately 5–11% of the population has this symptom at a given time . In adolescents, there is paucity of data. Mikkelsson et al. studied 1756 third- and fifth-grade schoolchildren and found widespread pain in 7.5% ( Table 1 ), but further investigations of CWP in children and adolescents are clearly warranted.
Recently, Macfarlane et al. conducted a study that compared the occurrence of CWP and analysed the potential aetiology behind differences in prevalence in Europe. The authors demonstrated that there is higher prevalence, particularly in Eastern Europe, which is due to adverse psychosocial factors including poorer psychological health and physical morbidities. The major limitation of this study is that it only included men and, it is known that CWP is more frequently diagnosed in middle- and older-age females .
Geographical variations have also been observed among patients with FMS. FMS is recognized as a common condition in the clinic and a major cause of morbidity worldwide. FMS has a different prevalence depending on the studied population and the diagnostic criteria used, ranging from 0.7% (Denmark) to 2.4% (Spain) ( Table 2 ).
In the first study that determined FMS prevalence in the general population of five European countries, using an identical methodology, Branco et al. found overall prevalence of FMS in the Italian (3.7%), Portuguese (3.6%), German (3.2%), Spanish (2.3%) and French (1.4%) general populations comparable to those already published. Of note, this study provided the first evidence of FMS prevalence in France and Portugal. In this survey, the estimated prevalence of FMS in the general population was age-related, reaching a peak prevalence in the group of 75–84 years. However, it is likely that these results could be overestimated in the elderly because ageing is associated with frequent co-morbidities that may result in widespread pain and/or fatigue. In this study, besides gender and age, the likelihood of having FMS did not appear to be affected by other socio-demographic variables.
What are the reasons for the different prevalence rates of FMS and CWP between various geographical regions?
Any ethnic differences in widespread pain prevalence may be a result of psychosocial or cultural differences, as well as genetic predisposition and the physical or social environment. If psychological and psychosocial factors influence the reporting of symptoms, and subjects at higher risk can be identified by past health and illness attitudes and beliefs, then it would be surprising if there were not differences in prevalence between countries because such risk factors or markers are likely to differ between populations of countries with distinct cultures . On the other hand, unfavourable climatic conditions and variations in sunlight exposure and vitamin D status may also influence musculoskeletal pain.
White and Thompson conducted a very interesting study in a community of Amish adults in Southwestern Ontario, having as a priori assumption that, if litigation and/or compensation availability have major effects on FMS prevalence, then FMS prevalence in the Amish should approach zero. The question was “Is it possible that individuals in this culturally isolated society express their FMS differently?” Strikingly, the authors found that FMS prevalence in the Amish was clearly greater than zero (7.3%). Somewhat surprisingly, FMS prevalence was higher in this population than in any other previously reported population. In accordance with this hypothesis, Jacobsson et al. verified that no subject in the Pima Indians reported chronic generalised musculoskeletal pain. The extremely low prevalence of CWP among Pimas also contrasts with the prevalence of inflammatory rheumatic diseases observed in these Native Americans; the reasons for these prevalence differences in two isolated communities might include genetic and/or environmental factors.
Geographical variation
Geographical differences in occurrence of chronic widespread pain
What is the importance of epidemiological studies of rheumatic diseases?
The study of the descriptive epidemiology of rheumatic diseases in several countries and areas around the world is of interest, as the occurrence of these diseases varies among different populations. Geographical, ethnic and racial factors can be determinant for their frequency and expression. In contrast to industrialised countries, the prevalence of rheumatic diseases in developing countries is largely unknown. The investigation of the epidemiological profile of rheumatic diseases in these countries can reveal the role of environmental and lifestyle factors characteristic of this populations, providing insights into the disease aetiology.
Why study CWP ‘and’ Fibromyalgia?
CWP is the cardinal symptom of the FMS, one of the most common reasons for referral to a rheumatologist.
Prior to 1990, several diagnostic criteria for FMS and CWP were available . In 1990, the ACR established the classification criteria for CWP , which is defined as pain above and below the waist, involving both sides of the body and lasting for at least 3 months, and for FMS, which includes CWP and the observation of pain brought on by pressure at specific anatomic sites. Previous studies did not use consistent criteria for this syndrome and, in particular, definitions of widespread pain differed. Therefore, we should not neglect the fact that minor differences in the definition of widespread pain can be reflected in the disease prevalence estimates .
Although CWP is the cardinal feature of FMS, the relation between these two clinical expressions of chronic pain is by no means clear. Neither CWP nor FMS appears as confined conditions, as with time, patients frequently move across different categories of pain syndromes . This supports the concept that chronic pain conditions may constitute a continuum of pain distribution from localised to widespread, rather than different entities. About 20% of the population with CWP also has 11 of 18 tender points , and in 70–80% of the patients who later develop FMS, the disease starts with localised and intermittent pain. The number of painful sites usually increases slowly over the years, before the patient finally develops the full-blown picture of FMS . It is not clear why some people with widespread pain also have a compatible FMS examination and others do not.
Very few studies have estimated the prevalence of CWP in the general population and there are currently no published robust international epidemiological data even though the classification criteria can be easily applied to an epidemiological context ( Table 1 ).
| Study | Year | Country | Age group | Prevalence (%) total | Prevalence (%) women |
|---|---|---|---|---|---|
| Forseth et al. | 1992 | Norway | 20–50 | NI | 15.3 |
| Croft et al. | 1993 | England | 18–79 | 11.2 | 15.6 |
| Wolfe et al. | 1995 | USA | 18+ | 10.6 | NI |
| Jacobsson et al. | 1996 | USA (Pima) | 35–70 | 0.0 | NI |
| Mikkelsson et al. | 1997 | Finland | Pre-adolescents | 7.5 | NI |
| White et al. | 1999 | Canada | 18+ | 7.3 | NI |
| Hunt et al. | 1999 | England | 18–65 | 4.7 | 5.3 |
| Buskila et al. | 2000 | Israel | 18+ | 9.9 | 14.0 |
| Lindell et al. | 2000 | Sweden | 20–74 | 4.2 | NI |
| Bergman et al. | 2001 | Sweden | 20–74 | 11.4 | NI |
| Storzhenko et al. | 2004 | Russia | 27–75 | 13.3 | NI |
| Mas et al. | 2008 | Spain | 20+ | 8 | NI |
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
