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RESEARCH REPORT |
1 Turner Dental School, The University of Manchester, Higher Cambridge Street, Manchester M15 6FH, UK; and
2 Department of Clinical and Health Psychology, Central Manchester Healthcare Trust, Manchester, UK;
* corresponding author, Tatiana.Macfarlane{at}man.ac.uk
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: orofacial pain • general population • outcome predictors • risk factors • prospective study • somatic symptoms
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The baseline study was conducted in 1997–98. A questionnaire was sent to a random sample of 4000 people aged 18–65 yrs registered with a general medical practice in South East Cheshire, North West England (Macfarlane et al., 2002a). Non-respondents to the first questionnaire were sent a postcard reminder, a further questionnaire, and, if necessary, a telephone call.
Participants reporting orofacial pain in the baseline survey were sent a follow-up questionnaire four years later (2001–02). The same questions on orofacial pain were asked as in the baseline survey. Similarly to the baseline survey, non-respondents were followed by a postcard reminder, a further questionnaire, and, if necessary, a telephone call.
Ethical approval for the study was granted by the Local Research Ethics Committee, and informed consent was obtained.
Study Questionnaire
Orofacial pain was defined as present if the respondent had experienced pain during the past month in at least one of the following: in the jaw joint/s, in the area just in front of the ear/s, in or around the eyes, when opening the mouth wide, shooting pains in the face or cheeks, in the jaw joint when chewing food, in and around the temples, tenderness of muscles at the side of the face, and prolonged burning sensation in the tongue or other parts of the mouth (Locker and Grushka, 1987).
Those who responded positively were asked about the commencement of pain, whether they had pain at the time of completing the questionnaire, frequency during the preceding month, and the duration of pain episodes. The intensity of the pain during the past month was measured on a numerical analogue scale ranging from 0 (no pain) to 10 (pain as bad as it could be). People who reported orofacial pain were also asked whether they took time off work, were unable to carry out usual activities, sought professional help, and took any medication for orofacial pain.
A sleep questionnaire (Jenkins et al., 1988) was used to measure sleep disturbance. Inquiry was also made, by both direct questions and illustrated body manikins, regarding pain in the body (during the preceding month). Widespread pain was defined according to the definition of the American College of Rheumatology (Wolfe et al., 1990). For the purpose of the current analysis, pain reported above the neck was not considered in determinations of whether widespread pain was present. Psychological distress was measured according to the 12-item General Health Questionnaire (Goldberg and Williams, 1988). Each item within this questionnaire consists of asking the subject whether he/she has recently (during the preceding few weeks) experienced a particular symptom, on a four-point Likert scale. Illness behavior was assessed based on the 30-item Illness Behaviour Questionnaire (Pilowsky and Spence, 1983).
Socio-economic class was measured by the Townsend Index (Townsend et al., 1988) and was determined from the postal code of each individual, according to the 1991 Census (Crown Copyright, 1991).
Statistical Data Analysis
The magnitude of association between an exposure and orofacial pain was described by the relative risk (RR). This is a more meaningful effect measure for representative cross-sectional studies than the Odds Ratio (Lee, 1994; Davies et al., 1998). Continuous variables were categorized by percentiles (quartiles, tertiles, or median) of the overall distribution. We used the Mantel-Haenszel test (Mantel and Haenszel, 1959) to examine heterogeneity by age and gender. We used Cox regression (Cox, 1972) to estimate relative risk adjusted for potential confounders (age and gender). The RR was considered significantly different from ‘1’ if the 95% confidence interval did not include ‘1’. We used a backward stepwise Cox regression model to identify a group of independent factors predicting outcome at 4 yrs.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The participation rate was higher in women than in men (P < 0.001), in older people (
2 test for trend, P < 0.001), and in people with a higher socio-economic class (P < 0.001). Therefore, only 11% of the participants at baseline were ages 25 years or younger, the majority were women (55%), and most participants lived in affluent areas (55%) as defined by the overall Townsend deprivation score distribution in England and Wales (Table 1
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). Only 12% of the participants with orofacial pain at baseline were 25 years or younger (Table 1).
Participation Rate at Follow-up
A total of 424 (66%) out of 646 individuals with orofacial pain at baseline participated at follow-up, giving an adjusted participation rate of 79%. This figure was obtained after we excluded those who were no longer registered with the practice (n = 106), who were deceased, who were unable to complete the questionnaire due to illness or disability (n = 3), or who expressed a wish at baseline not to be contacted again (n = 1). The participation rate was higher among women (2 test, P = 0.01), older individuals (2 test, P < 0.001), and people with a higher socio-economic class (2 test, P < 0.001). Consequently, only 9% of the participants at baseline were 25 years or younger, the majority were women (68%), and most participants (58%) lived in affluent areas as defined by the overall Townsend deprivation score distribution in England and Wales (Table 1).
Description of Outcome after Four Years
Of the 424 participants with orofacial pain at baseline, 229 (54%) reported orofacial pain four years later, and 195 (46%) did not report such pain. The distribution by type of orofacial pain was similar between the two time periods (McNemar test, P > 0.05), except for pain in or around the temples, which increased at follow-up (McNemar test, P < 0.001). Among those with each specific type of pain, the proportion reporting the same pain at follow-up was between 32% and 76%.
Predictors of Long-term Outcome of Orofacial Pain
No heterogeneity by age or gender was found for any of the potential predictors. Women were more likely to report persistent orofacial pain than men, and the risk increased with age. Most pain characteristics predicted orofacial pain persistence, with the lowest risk reported for pain at the time the questionnaire was completed (RR, 1.3; 95% CI, 1.0–1.7), and the highest risk for taken time off work because of orofacial pain (RR, 1.7; 95% CI, 1.2–2.4) (Table 2). Backward stepwise Cox regression modeling identified two baseline pain characteristics that associated with persistence of orofacial pain: medication for orofacial pain and taken time off work because of orofacial pain.
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). Backward stepwise Cox regression modeling identified two baseline factors that were associated with persistence of orofacial pain: widespread body pain and General Health Questionnaire score 4–12.
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). Out of 23 subjects with orofacial pain at baseline and responding positively to four or all five factors in the final model, 18 (78%) reported orofacial pain on the follow-up survey.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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In our study, women and individuals aged over 54 years with orofacial pain at baseline were more likely to report orofacial pain four years later. We have shown that pain characteristics, aspects of illness behavior, psychological distress, and widespread body pain at baseline predict persistent orofacial pain. These findings support results from studies of other types of body pain, which showed that psychological distress and features of somatization (Macfarlane et al., 1996; McBeth et al., 2001; Papageorgiou et al., 2002) predict persistence of chronic widespread body pain. Croft et al.(2003) examined consultation data from general practice records of 10,073 women and pain complaints after 25 years. While this study provided support for shared mechanisms of chronicity across regional pain complaints, there was strong evidence of unique regional influences on chronicity as well.
Several methodological issues need to be discussed when the study results are considered:
First, how representative was the study population? Since over 99% of the United Kingdom population is registered with general practitioners (Department of Health, 2002), and access to most health service care is through the general medical practitioner, this provided a convenient sampling frame for the local population. The National Health Service in the United Kingdom was set up in 1948 to provide health care for all citizens, based on need, not the ability to pay. It is made up of a wide range of health professionals, support workers, and organizations, and is recognized by the World Health Organization as one of the best health services in the world. As part of the National Health Service, general practitioners look after the health of people in their local community and deal with a whole range of health problems. Every United Kingdom citizen has a right to be registered with a local general practitioner, and visits to the surgery are free (NHS, 2004).
The current population sample is not fully representative of a population of the UK. Instead, it is a sample of the population of one area. Based on the 1991 population Census, the Borough of Congleton, where the study was conducted, and the patients registered at the medical practice had age-gender distribution similar to that for England and Wales, although a higher proportion of people own their houses (Macfarlane et al., 2002a). Evidence from other studies of risk factors and predictors of outcome would suggest that, although populations are different in socio-economic characteristics, they are unlikely to differ in factors that cause and predict the outcome of symptoms. In this sense, the study is population-based, with the only selection being that the subject chooses not to participate. This is in contrast to studies among clinical samples that may be selected particularly on factors such as psychological factors, which are strong predictors of outcome.
While the participation rate at follow-up was acceptable, the possible effects of non-participation bias need to be considered. Non-participants were more likely to be male, younger, and from a lower socio-economic background. Nevertheless, these differences would affect the comparisons in the present study only if the relationship between these factors and the persistence of orofacial pain were different in those subjects who participated compared with those who did not. This seems unlikely.
All possible efforts were made to increase the level of participation. Questionnaires were posted together with a covering letter from the general medical practitioner informing practice members of the practice participation in the study. A reply-paid envelope was enclosed. Simultaneously, a press release about the study was broadcast on the local radio and was published in the local new paper. Posters about the study were placed in the medical practice. Non-respondents were followed up by postcard reminder, a further questionnaire, and, if necessary, a telephone call.
Second, people in the present study were assessed at two time points four years apart, and prevalent cases of orofacial pain were identified at these two time points. We do not know what happened in the intervening years. It is possible that individuals who were classified as having orofacial pain at baseline may have had symptoms which resolved during that period and then reported new orofacial pain at follow-up. We could have attempted to determine what had happened during the four-year period, but recall of pain symptoms over such a long period would almost certainly have been unreliable.
Third, we conducted a study of orofacial pain syndrome as a single entity defined by a postal questionnaire, rather than as individual clinical entities. One of the reasons for this was that, for these conditions, there are currently no classification criteria which are suitable for use in large-scale population studies, and little evidence, on etiological grounds, for their separate consideration. Nevertheless, it will be important for future studies to determine the rationale (on etiological grounds) for distinct clinical entities which might have physical and/or psychological causes.
Finally, this study has demonstrated for the first time that, for those persons with disabling orofacial pain and additional features of widespread body pain and maladaptive response to illness, their prognosis after four years is worse than for individuals without such additional features, regardless of whether these features precede or are a consequence of pain at baseline.
To summarize, we have found that, of those persons selected from the community with self-reported orofacial pain, just under half will have symptoms that will resolve after four years. Persons with pain that requires medication, other body pain, and psychological distress are more likely to have symptoms that persist. These findings have important implications for the identification and treatment of patients with orofacial pain.
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ACKNOWLEDGMENTS |
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Received September 30, 2003; Last revision June 21, 2004; Accepted June 23, 2004
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REFERENCES |
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