REVIEW

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Epidemiology of neuropathic pain

Practice Points

Blair H Smith†1 & Nicola Torrance1

„„

Lack of agreed definitions and diagnostic criteria for neuropathic pain hamper epidemiological studies.

„„

Neuropathic pain is probably more common than previously thought, with 6–8% of adults in the general population reporting chronic pain with neuropathic characteristics, around 20% of patients with long-standing diabetes and around 8% of those who have had shingles.

„„

Neuropathic pain is likely to become more common in future because of aging populations and improved recognition.

„„

Compared with other forms of chronic pain, neuropathic pain leads to greater detrimental impact on activities of daily living and lower health-related quality of life.

SUMMARY

Epidemiology is an essential clinical tool in designing and evaluating management and prevention strategies, and is particularly relevant to neuropathic pain. Despite its relevance to neuropathic pain however, there is a paucity of accurate information on its prevalence, distribution and determinants, for several reasons. In many ways, it is appropriate to study neuro­ pathic pain merely as a symptom or a pain mechanism rather than a specific disease. However, the different causes display sufficient similarities in their clinical and personal impact, and in their response to treatment, to make it worthwhile to consider neuropathic pain as a distinct condition. There are, however, important specific disease-based factors that need to be considered separately. Older estimates of the prevalence of neuropathic pain (based on specific diagnoses) tend to be lower (1–2%) than newer estimates that are based on questionnaires examining classic symptoms (6–8%). Further methodological research is needed to clarify these. Associated poor general health is a feature of all neuropathic pain, similar to other severe chronic diseases. Epidemiology of neuropathic pain Despite rapid advances in our understanding of the mechanisms and assessment of neuro­ pathic pain, we lack accurate information on its prevalence and risk factors at a population level. There are good reasons for this, and

these will be explored in this article, along with the steps being taken to address the knowledge gap. It is important to strive for a good epidemiological understanding of neuro­ pathic pain, to allow improved prevention and management.

Aberdeen Pain Research Collaboration, Centre of Academic Primary Care, University of Aberdeen, Foresterhill Health Centre, Westburn Road, Aberdeen AB25 2AY, Scotland, UK † Author for correspondence: Tel.: +44 122 455 3990; Fax: +44 122 455 0683; [email protected] 1

10.2217/PMT.10.5 © 2011 Future Medicine Ltd

Pain Manage. (2011) 1(1), 87–96

ISSN 1758-1869

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Review  Smith & Torrance Epidemiology Epidemiology is defined as, “the study of the occurrence and distribution of health-related states or events in a specified population, includ­ ing the study of the determinants influencing such states, and the application of this know­ ledge to control health problems” [1] . The first half of this definition implies the need for mea­ surement and observation, and needs maximum statistical and clinical precision. With these in place, the second half of the definition makes epidemiology an exciting and important disci­ pline, of primary relevance to physicians and to society. One of the strengths of the epidemiological approach is that it can allow the development of successful strategies to prevent and manage diseases even without a full understanding of their underlying etiological mechanisms. Early epidemiological research in diseases such as scurvy, cholera and cancer identified impor­ tant and influential preventive measures many years before the underlying mechanisms were understood. In addition, the proven associations indicated the direction of subsequent scientific approaches to the diseases, further enriching our understanding and the development of therapeu­ tic approaches. The same is likely to be true for neuropathic pain, with epidemiological, clini­ cal and basic scientific research combining to improve treatment and prevention. Challenges to the epidemiology of neuropathic pain The first important step in epidemiological research is to establish a valid case definition that truly reflects the condition under exami­ nation. Sometimes this is straightforward, but represents our first barrier in the epidemiology of neuropathic pain. For epidemiological pur­ poses, a case definition needs to be applicable in a population-based study, and cannot generally rely on detailed clinical, laboratory or radiologi­ cal examination. The International Association for the Study of Pain (IASP) defines it formally as, “pain initiated or caused by a primary lesion or dysfunction in the nervous system” [2] . A more recent international consensus amended this to, “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system” [3] , although this definition has not been adopted by the IASP. On close examination it can be seen that the differences between these, although small, are important, and also that both present

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problems for population-based research. Even if agreement between these competing definitions were achieved however, we would still need to clarify precisely what constitutes a ‘(primary) lesion’ or ‘disease’ and whether a diagnosis (or case) of neuropathic pain can be established without absolute proof of the presence of these. This brings us to our second challenge: case ascertainment. Even if a practical case definition for neuropathic pain can be agreed, we need to consider how to identify those in the population who do and who do not fulfill this definition. Whereas ascertainment of many types of chronic pain can rely on patient-defined subjective assess­ ment, the ascertainment of neuropathic pain requires a clinical component. However, even in a specialist clinical setting there is no ‘gold standard’ for determining whether or not an individual has neuropathic pain. There is inter­ national consensus on the assessment of neuro­ pathic pain in the primary care setting  [4] and potentially in the specialist clinic [5] . However, whilst these detailed approaches are important for ascertaining neuropathic pain in individuals, they are too resource-intensive and impractical for the large-scale population-based studies that are the basis of epidemiology. An additional complexity is added by the emerging recognition that pain is not a binary phenomenon (neuropathic or nociceptive) as traditionally taught. Instead, neuropathic characteristics contribute to different pains to different extents and pain can be ‘more or less neuropathic’ [6,7] . Pain is therefore a spectrum, and we need to identify the clinically relevant level of neuropathic contribution and to deter­ mine the point on this spectrum at which it is valid to ascertain a case of neuropathic pain in any epidemiological study. This should mainly be determined by clinical relevance (i.e., the response to specific neuropathic pain treatments at different points on the spectrum), and this is currently unknown. Is neuropathic pain a single entity? There is a fundamental discussion regarding the relevance of considering neuropathic pain as a single, global entity, rather than as a number of different conditions, with different patho­ logies that are grouped together for reasons of convenience. It is certainly true that there are many clear differences in the etiology of diseases such as postherpetic neuralgia (PHN), painful diabetic neuropathy (PDN) and HIV-related

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Epidemiology of neuropathic pain  neuropathy. These differences have obvious implications for prevention and management of these distinct conditions and there is therefore much to be gained from the separate study of their epidemiology [8] . However, there are also good reasons for studying the global condition of neuropathic pain, particularly from the population or pri­ mary care perspective. First, whatever the under­ lying cause is, physicians see a common pattern of signs and symptoms suggesting a single dis­ ease entity. Second, the impact of the pain on the individual sufferer is much less dependent upon its cause than its severity [9] . Third, at the patho­ logical level, although there are important differ­ ences in the pathophysiological mechanisms of different neuropathic pain conditions, there are also many similarities irrespective of the under­ lying lesion or disease. Most importantly from a clinical point of view, especially in primary care (where the majority of those with neuro­ pathic pain present and are managed), there are many similarities in responses to treatment. Because these responses differ importantly from responses in non-neuropathic pain (pharmaco­ logically [10–12] and nonpharmacologically [13]), it is valid to assess and manage neuropathic pain as a single, separate clinical entity (while still ensur­ ing that treatable underlying causes are isolated and addressed). In this respect it is analogous to epilepsy. Indeed, clinically it will often be impossible to distinguish a precise neurological diagnosis without resorting to expensive and time-consuming investigations, and this will be unnecessary if therapeutic benefit is obtained with standard treatments. This uncertainty will also be apposite to epidemiological research, but so perhaps is the relevance of a blunt, inclusive approach to case ascertainment. However, current and emerging research suggests that such a comparatively simplistic approach will be permissible. For example, there is evidence of at least two different subtypes of PHN, perhaps with different responses to topi­ cal treatment [14] . Recently, through detailed assessment of symptoms and sensory profiles, Baron et al. identified five distinct subtypes of neuropathic pain, and found that these occurred at different frequencies in different neuro­ pathic conditions [15] . If these subtypes prove to have different responses to treatment, there are clear implications for clinical management, and therefore also for epidemiology. Even more recently there is evidence that the effectiveness

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Review

of treatment for burning mouth syndrome dif­ fers depending upon whether the mechanism is peripheral or central [16] . There is a strong argu­ ment for targeting the treatment of pain spe­ cifically according to its underlying mechanism and likely response, and this may be particularly true for neuropathic pain [17] . As well as further knowledge of neuropathic mechanisms however, this also requires consideration of individual genetic factors and there is still much research to be done before a mechanism-based approach can be applied in a clinical setting. Most ran­ domized controlled trials that underpin the evi­ dence for treatment of neuropathic pain have been based on distinct diagnostic classifications (mainly PDN and PHN) and we cannot assume that success (or failure) of a drug in one dis­ ease can be translated to other conditions. For example, in HIV-related neuropathy, treatment with amitriptyline and gabapentin, two of the standard pharmacotherapies in neuropathic pain, have been shown to be relatively ineffec­ tive [18–20] ; by contrast, there is some evidence for the effectiveness of nonstandard treatment with cannabis [21,22] . The more such findings become apparent, the greater the need for subdividing the epidemiology of neuropathic pain. Finally, although most neuropathic pain is assessed and managed by nonspecialists, pain specialists and neurologists require more com­ plex tools for assessment, and treatment modali­ ties that are specific to individual diagnoses. Such specialist approaches will not be informed by a blunt population-based approach to neuro­ pathic pain as a single global entity, and more precision is required for these purposes. Current knowledge of the epidemiology of neuropathic pain Despite these challenges and their effect on our ability to describe the epidemiology of neuro­ pathic pain accurately, we do have some evidence that is informative and useful. Initial, well-estab­ lished estimates of the prevalence of neuropathic pain were based on summed estimates of the prevalence of the main neuropathic conditions: approximately 2% in the USA [23] and 1% in the UK [24] . The validity of these estimates is sup­ ported by their reasonable similarity, but they are likely to be inaccurate for a number of reasons: ƒƒ They can only include individuals who have,

or who report, formal diagnoses of traditional neuropathic pain conditions, and must

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Review  Smith & Torrance exclude those with idiopathic or unrecognized neuropathic pain, and those with a neuro­ pathic contribution to more traditionally ‘nociceptive’ pain [6,7] ; ƒƒ The studies they are based on are old and

likely to have been superseded by epidemio­ logical research of higher quality and greater reflection of current demography; ƒƒ On the other hand, they will ‘double count’

individuals who have more than one cause of neuropathic pain. On balance, these figures probably under­ estimate the true prevalence [25] . Although it is difficult to identify all cases of neuropathic pain in the population, it appears increasingly likely that many more people experience neuro­ pathic symptoms than have been diagnosed with neuropathic pain in the past. However, we do have evidence of the epi­ demiology of the important specific causes of neuropathic pain. For example, there are many estimates of the prevalence of diabetes melli­ tus (e.g., the prevalence of diabetes for all age groups worldwide was estimated to be 2.8% in 2000, rising to 4.4% in 2030 [26] ; more than 220  million people worldwide have diabe­ tes [101] ), the incidence of herpes zoster (~24% per lifetime [27] ) and the prevalence of HIV (with 33.2 million people affected worldwide in 2007 [102]). There are an increasing number of well-conducted studies that demonstrate and describe the proportion of individuals who have these conditions that experience neuropathic pain, and some of these will allow extrapola­ tion to general population prevalences. For example, 20.1% of those with Type 2 diabetes were found to have painful peripheral neuro­ pathy in a detailed two-stage study [28] ; 8.0% of those diagnosed with herpes zoster infection had subsequent PHN [29] ; and, in a German primary care population, a predominantly neuropathic component was found in 37.0% of those with chronic low back pain [30] . A number of neuropathic pain screening instruments have been developed, based on the presence of characteristic symptoms and signs. These are intended for use either in popula­ tion-based research and/or clinical work [31] , were mainly validated in pain clinic samples, and have reasonable sensitivity and specificity. Although their positive predictive value in the

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validation samples has been calculated, this is likely to be rather different in general popula­ tion samples [32] where the underlying preva­ lence of neuropathic pain is much lower. Their absolute value in population-based research is therefore limited without concurrent validation in this setting, but they can nonetheless provide some interim estimates of the prevalence of pain with neuropathic features in large general popu­ lations. For example, in the UK Torrance et al. reported a prevalence of “pain of predominantly neuropathic origin” of 8.2% [33] , and Bouhassira et al. reported a prevalence of “chronic pain with neuropathic features” of 6.9% in France  [34] . The screening instruments used for these two studies, although developed independently, were remarkably similar and again, validity of the prevalence estimates is suggested by their similarity. It may be that this represents ‘pos­ sible’ neuropathic pain with further classifica­ tion into ‘probable’ or ‘definite’ neuropathic pain requiring detailed clinical examination [3] . There is gathering evidence for clinical and psychosocial factors that are associated with neuropathic pain at a population level. They include older age, female gender, occupational factors (manual working), indicators of depri­ vation (e.g., lower educational level or poorer housing status) and poor general health. Most of this research is based on cross-sectional stud­ ies and it is generally impossible to distinguish cause from effect. For example, it is not clear whether poor health predisposes individuals to neuropathic pain or vice versa. Longitudinal studies would be required for this and these would help to identify: ƒƒ Risk factors (those factors that pre-exist neuro­

pathic pain, make the development of neuro­ pathic pain more likely and are relevant for prevention); ƒƒ Impact factors (those factors that are the result

of neuropathic pain and treatment of which are likely to lead to overall improvement in pain); ƒƒ Confounding factors (those factors that co-

exist with neuropathic pain, but are neither the cause nor result of pain and are irrelevant in treatment); ƒƒ Modifying variables (those factors that co-

exist with neuropathic pain as a result of common etiological factors, and that may exacerbate or attenuate the pain).

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Epidemiology of neuropathic pain  Importantly, health-related quality of life scores in those with neuropathic pain have been found to be worse than in those with non-neuropathic pain [35] , and the most important determinant of health-related quality of life was shown to be the intensity of neuropathic pain [9] . The low health-related quality of life scores associated with neuro­pathic pain were broadly similar to those found in individuals with coronary artery disease or after recent myocardial infarction, with clinical depression, or with poorly controlled ­diabetes [35] . In addition to these factors associated with neuropathic pain in general, specific, potentially modifiable risk factors have been found for specific conditions such as PDN (including smoking, high glycosylated hemoglobin and duration of diabe­ tes) [36,37] , PHN (including severe acute pain) [38] and postsurgical pain (including peri-operative pain, some surgical techniques and anxiety) [39] . Looking at these risk factors, it is clear that the burden of neuropathic pain is likely to increase. As society ages, so does the risk of neuropathic pain (along with both the incidence and prevalence of diseases, such as diabetes, that are associated with it). Of course, prevention based on epidemiology should also consider the underlying risk factors for the separate conditions, and a public health approach, including reduction in obesity, smok­ ing and risk of HIV, will reduce the burden of many of the causes of neuropathic pain (including diabetes, diseases leading to surgery and HIV).

Review

Literature review We conducted a comprehensive literature review of population-based studies of the epidemio­logy of neuropathic pain, from 1996 to 2008 on Medline. Studies were included if they focused on neuropathic pain in a general population set­ ting (including, where relevant, primary care), but not if they included only specific patient or clinic groups. This was in order to identify a population prevalence; some studies were based in primary care in countries where the primary care population is almost equivalent to the general population, and therefore these studies were included. In summary, this review identified five stud­ ies examining the epidemiology of neuropathic pain as a single entity (prevalence ranging for 3.3 to 17.9%) (Table 1) [33,34,40–42] . It is likely that such heterogeneous prevalence estimates are a function of the methodology rather than true regional differences. In the study by Dieleman et al., the annual incidence of neuropathic pain in the general population was estimated to be almost 1% [40] . An important main strength of this study is its large sample size obtained by a systematic search of computerized medical records, fol­ lowed by a manual review. However, as with the other estimates of prevalence, there are a number of weaknesses in this approach. This method­ology only detects those who have pre­ sented to primary care; the identification of the

Table 1. Prevalence of pain with neuropathic characteristics in the general population. First author Location (year) (sample size)

Study method

NeuP case ascertainment method/instrument

Definition

Prevalence (%)

Bouhassira et al. (2008)

France (23,712)

Postal survey, general population sample

DN4 questionnaire

6.9

[34]

Dieleman et al. (2008)

General practice research database

0.8†

[40]

Gustorff et al. (2008)

The Netherlands (9311) Austria (7707)

‘Chronic pain with neuropathic characteristics’ ‘Neuropathic pain’

‘Neuropathic pain’

3.3

[41]

Torrance et al. (2006)

UK (3002)

8.2

[33]

Toth et al. (2009)

Canada (1207)

‘Pain of predominantly neuropathic origin’ ‘Chronic pain with neuropathic pain symptoms’

17.9

[42]

Search using free text and ICPC codes, then manual review of the electronic patient records Interview survey ‘performed via Selected items from LANSS internet inquiry’ – preregistered and DN4 pool, representative of general population Postal survey, general S-LANSS population sample Computerized telephone interview of a random sample of the general population

DN4 questionnaire

Ref.

Dieleman et al. give the incidence, not the prevalence. DN4: Douleur Neuropathique en 4 Questions; ICPC: International Classification of Primary Care; LANSS: Leeds assessment of neuropathic symptoms and signs; NeuP: Neuropathic pain; S-LANSS: Self-complete Leeds assessment of neuropathic symptoms and signs. †

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Review  Smith & Torrance cases relies on accurate diagnoses of neuropathic pain (conditions), an accurate coding system and a method of these being identified through the computerized search and case notes review. Two of the studies in Table 1 were designed to administer validated case ascertainment instruments in large general population sam­ ples [33,34] ; however, other studies were not as rigorous. In a study by Toth et al. [42] , the use of the Douleur Neuropathique en 4 Questions (DN4) questionnaire in a telephone survey has not been previously validated, and in the study by Gurstoff et al. [41] , only selected items from two different screening tools were adminis­ tered. Furthermore, the representativeness of this study [41] , conducted via ‘internet inquiry’, is unclear. Overall, the self-report methods employed by these studies are useful in provid­ ing an indication of the population prevalence [33,34,41,42] . Further clinical examination stud­ ies based on these instruments are required to validate them in population-based research and allow more accurate calculation of the prevalence of neuropathic pain. There were 11  papers examining specific neuro­pathic pain diagnoses (Table  2) . These studies included: ƒƒ PHN – four in total, prevalence ranging from

2.6 to 7.2% of those experiencing shingles [29,43–45] ; ƒƒ Two relating to neuropathic pain originating

in the back – population prevalence of back pain with ‘neuropathic components’ approxi­ mately 13% in Germany [30] and of ‘discrelated sciatica’ approximately 2.2% in Tunisia [46] ; ƒƒ PDN – two,

[47,48] – prevalence 8% 20% [47] of those with diabetes;

[48]

and

ƒƒ Supraorbital neuralgia  –  one, estimated

­prevalence 0.5% in Norwegian adults [49] ; ƒƒ Two of multiple neuropathic pain conditions

from a review of computerized primary care records [50,51] . Two literature review papers examining the epidemiology of specific neuropathic pain diagnoses were also identified (Table 3) [52,53] . These were able to estimate general population incidence rates for five of these conditions, but, with the exception of carpal tunnel syndrome, could only identify prevalence rates for diseasespecific subgroups. The case identification and ascertainment methods included interview

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surveys with or without standardized identifi­ cation instruments and/or brief clinical exami­ nation; mail surveys with a range of diagnostic instruments; and computerized medical records reviews. Thus, there was considerable hetero­ geneity in the methods, and therefore in the results of the studies identified in the search. The results therefore throw up as many ques­ tions as they answer, but nonetheless provide an interim understanding of the epidemiology of neuropathic pain, and should inform future epidemiological research. Conclusions & future perspective In summary, we can conclude that neuropathic pain is both common and important (to individ­ uals and society), and we have some indication of the size of the problem, globally and of spe­ cific causes of neuropathic pain. This research should heighten our awareness of the problem. This, along with the growing evidence of associ­ ated clinical, sociodemographic and risk factors, provides indicators of where to target educa­ tion and treatment, and suggests opportunities for prevention. However, the available information is far from perfect, and more work is needed, so that we might progress towards a better under­ standing of neuropathic pain in the population. This should be based on sound epidemiological principles and developing consensus on defi­ nition and assessment. The development of an agreed, practical definition of neuropathic pain for epidemiological research is important, as is an understanding of how the results of ques­ tionnaire-based screening instruments in the general population relate to clinically assessed neuropathic pain. Meanwhile, the availability of data from large computerized routine pri­ mary care databases is increasing, but the qual­ ity of this needs to be assured if we are to use these to assess the prevalence and health-related impact of neuropathic pain on a large scale. The development and refinement of disease-specific assessment instruments should continue to allow further detailed epidemiology of these conditions and of the proportions affected by neuropathic pain. Most research to date has been in cross-sectional studies, which are informative but limited in their scope. Longitudinal studies are more expensive and time-consuming, but are required for the identification of modifi­ able risk factors, distinguishing causal factors

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UK (2,900,000)

Iceland (421)

Hall et al. (2008)

Helgason et al. (2000) Opstelten et al. (2002) Sjaastad et al. (2004)

USA (1669)

France (1023)

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Interview survey (not clear whether face-to-face or telephone)

Database records from healthcare systems

Annual prevalence 2.2% Point prevalence 0.75%

Incidence rate of 3.4 per 1000 person-years

Prevalence 8%

Prevalence 0.5%

Supraorbital neuralgia PDPN

Prevalence 2.6% 3 months after onset of HZV

Incidence per 100,000 person-years: PHN: 40.2, TN: 26.8, PLP: 1.5, PDN: 15.3 Prevalence unknown Age standardized incidence per 100,000 person-years: PHN: 27.3, TN: 26.7, PLP: 0.8, PDN: 26.7 Prevalence unknown Prevalence 7.2% 3 months after onset of HZV

PHN

PHN

PHN, TN, PLP, PDN

LBP with a predominantly neuropathic component PHN, TN, PLP, PDN

Prevalence 20.1% of those with Type 2 diabetes (26.4% of those with Type 2 diabetes responding positively to DNS score question and attending for assessment) Population prevalence 14.5% of women, 11.4% of men (37.0% of those with chronic LBP)

PDPN

Diagnostic or procedure code PHN that might indicate a new case of HZV (ICD-8 codes 052.xx) Standardized questionnaire and DRS clinical examination

Prospective cohort telephone Nonstandard questions to interview study individuals diagnosed with HZV Computerized medical records review Coded and free text diagnosis of HZV and PHN Interview survey Standardized headache questions and clinical examination Computer-aided telephone survey Portion of the MNSI, BPI

Coded diagnosis of conditions in medical records (Read codes)

painDETECT questionnaire

Incidence 0.003% (8.0% of HZV)

Prevalence/incidence

PHN

NeuP condition

[46]

[43]

[48]

[49]

[44]

[45]

[51]

[50]

[30]

[47]

[29]

Ref.

BPI: Brief pain inventory; DNS: Diabetic Neuropathy Symptom; DRS: Disc-related sciatica; HZV: Herpes zoster virus; LBP: Low back pain; MNSI: Michigan neuropathy screening instrument; NeuP: Neuropathic pain; PDN: Painful diabetic neuropathy; PDPN: Painful diabetic peripheral neuropathy; PHN: Postherpetic neuralgia; PLP: Phantom limb pain; TCSS: Toronto clinical scoring system; TN: Trigeminal neuralgia.

Younes Tunisia (4380) et al. (2006)

Wu et al. (2007) Yawn et al. (2007)

Computerized medical records review Coded diagnosis of conditions in medical records (Read codes)

UK (6,800,800)

Hall et al. (2006)

The Netherlands (837) Norway (1838)

Computer-administered survey of primary care attenders with chronic LBP

Freynhagen Germany (7772) et al. (2006)

Computerized database of primary care records

Automated medical records review, general population sample Postal survey and clinical assessment

Choo et al. USA (250,000) (1997) Davies et al. UK (353) (2006) Clinical diagnosis (recorded or likely) One item from the DNS score; TCSS

Study method

First author Location (year) (sample size)

NeuP case ascertainment method/instrument

Table 2. Prevalence of specific neuropathic pain diagnosis in the general population.

Epidemiology of neuropathic pain 

Review

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To identify studies Literature review investigating the Medline (Pubmed) occurrence (incidence Up to February 2005 and prevalence) of neuropathic pain, its natural history, and its health and economic burden

Taylor (2006)

Searched terms were epidemiology OR incidence OR prevalence AND neuropathic pain OR conditions (named)

Inclusion: population-based studies or large case series in instances where no populationbased studies were identified; English language papers were the primary source, although relevant studies were translated; Searched for epidemiology papers in combination with appropriate terms identifying the syndrome of condition

No concise information given on the number of papers/ studies included in review, or of sample size; Summary table of incidence and prevalence estimates (where available) includes data from general population and diagnostic groups samples; Difficult to identify the source of the original data 12 studies of incidence and prevalence estimates: USA (six), UK (two), Sweden (two), Iceland (one), Spain (one); Design: four prospective database studies, three surveys, five not stated

Study inclusion/exclusion criteria Number/type of studies, definitions of NeuP, total sample number

Incidence: CRPS I: 5.5/100,000 CRPS II: 0.8/100,000 Prevalence: PHN: 6.8–38.3/100,000 (Iceland), 185/100,000 (USA) DN: 54/100,000 (UK), 1140/100,000 (USA), 222/100,000 (USA) Note: DN not necessarily pain NeuP back and leg pain: 778/100,000 (USA), 7600/100,000 (USA pain intense, disabling and chronic), 5800/100,000 (UK, disability pension), 6500/100,000 (Spain) CRPS I: 20.6/100,000 (Sweden) CRPS II: 4.2/100,000 (Sweden), 48/100,000 (USA)

Incidence: PHN: 11–40/100,000 TN: 4.7–26.8/100,000 (GP) Glosspharynegeal neuralgia: 0.8/100,000 (GP) Cervical radiculopathy: 83.2/100,00 (GP) Carpal tunnel syndrome: 105–276/100,000 (GP) Prevalence: Carpal tunnel syndrome: 2–16% (GP) Note: incidence and prevalence estimates for disease-specific populations not shown

Main findings – GP only

CRPS: Complex regional pain syndrome; DN: Diabetic neuropathy; DPN: Diabetic peripheral neuropathic pain; GP: General population; PHN: Postherpetic neuralgia; TN: Trigeminal neuralgia.

Summarize what Literature review is currently known Medline regarding the No dates available incidence and/or prevalence of DPN, PHN and other less common neuropathic pain conditions

Sadosky et al. (2008)

Review type, databases used, time period covered

Research question

Author (year)

Table 3. Review papers examining the epidemiology of specific neuropathic pain diagnoses.

[53]

[52]

Ref.

Review  Smith & Torrance

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Epidemiology of neuropathic pain  from outcomes of disease. Ultimately, the goal of this endeavor should be to establish and trial treatment and prevention strategies based on the identified risk factors and outcomes. Newer epidemiological techniques (including genetic epidemiology), and parallel research on the biological mechanisms of neuropathic pain are equally important. Ideally, these research modal­ ities should not proceed in isolation, but both inform and be informed by each other.

Bibliography Papers of special note have been highlighted as: of interest of considerable interest

Financial & competing interests disclosure The authors are in receipt of an unrestricted educational grant from Pfizer UK Ltd for a study on the epidemiology of refractory neuropathic pain. The authors have no other relevant affiliations or personal financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials ­discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.

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Doth AH, Hansson PT, Jensen MP et al.: The burden of neuropathic pain: a systematic review and meta-analysis of health utilities. Pain 149(2), 338–344 (2010).

10

Finnerup NB, Otto M, McQuay HJ, Jensen TS, Sindrup SH: Algorithm for neuropathic pain treatment: an evidence based proposal. Pain 118(3), 289–305 (2005).

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Dworkin RH, O’Connor AB, Backonja M et al.: Pharmacologic management of neuropathic pain: evidence-based recommendations. Pain 132(3), 237–251 (2007).

n

n n

1

Porta M: A Dictionary of Epidemiology (5th Edition). Oxford University Press, New York, NY, USA (2008).

2

Merskey H, Bogduk N: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. IASP Press, Seattle, WA, USA (1994).

3

n

4

5

n n

6

7

8

Loeser JD, Treede RD: The Kyoto protocol of IASP basic pain terminology. Pain 137(3), 473–477 (2008). Summarizes the current international agreement on pain definitions, including neuropathic pain; crucial as a starting point for epidemiological study.

Haanpaa M, Attal N, Backonja M et al.: International Association for the Study of Pain NeuPSIG guidelines on neuropathic pain assessment. Pain (2010) (Epub ahead of print). Provides a wide-ranging, in-depth review, based on current evidence, of all aspects of neuropathic pain assessment, from screening instruments in populations to laser-evoked potentials for Ad fiber pathways. Bennett MI, Smith BH, Torrance N et al.: Can pain be more or less neuropathic? Comparison of symptom assessment tools with ratings of certainty by clinicians. Pain 122(3), 289–294 (2006). Attal N, Fermanian C, Fermanian J, Lanteri-Minet M, Alchaar H, Bouhassira D: Neuropathic pain: are there distinct subtypes depending on the aetiology or anatomical lesion? Pain 138(2), 343–353 (2008). Crombie IK, Croft PR, Linton SJ, LeResche l, Von Korff M: Epidemiology of Pain (1st Edition). IASP Press, Seattle, WA, USA (1999).

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Pain Manage. (2011) 1(1)

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Websites

101 WHO mediacentre diabetes factsheet

www.who.int/mediacentre/factsheets/fs312/ en/index.html 102 WHO HIV/AIDS data and statistics

www.who.int/hiv/data/en/index.html

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Epidemiology of neuropathic pain.

Epidemiology is an essential clinical tool in designing and evaluating management and prevention strategies, and is particularly relevant to neuropath...
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