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Predictors of Outcome for Orofacial Pain in the General Population: a Four-year Follow-up Study
1 Turner Dental School, The University of Manchester, Higher Cambridge Street, Manchester M15 6FH, UK; and Correspondence: * corresponding author, Tatiana.Macfarlane{at}man.ac.uk
Orofacial pain is often persistent, but it is not clear why it lasts in some patients but not in others. We aimed to describe the natural course of orofacial pain in a general population sample over a four-year period and to identify factors that would predict the persistence of pain. A cross-sectional population-based survey was conducted in the United Kingdom, involving 2504 participants (participation rate 74%), of whom 646 (26%) reported orofacial pain. Overall, 424 (79% adjusted participation rate) of these individuals participated at the four-year follow-up, of whom 229 (54%) reported orofacial pain and 195 (46%) did not report such pain. Persistent orofacial pain was associated with females, older age, psychological distress, widespread body pain, and taking medication for orofacial pain at baseline. These findings may have implications for the identification and treatment of patients with orofacial pain.
Key Words: orofacial pain • general population • outcome predictors • risk factors • prospective study • somatic symptoms
Cross-sectional studies indicate that, at any time, about one in every four adults will have experienced orofacial pain during the preceding month (Locker and Grushka, 1987; Locker et al., 1991; Macfarlane et al., 2002a). This is higher in women than in men (Von Korff et al., 1988; Locker et al., 1991; Macfarlane et al., 2002a), and generally the greatest risk of symptoms was reported among younger people (Von Korff et al., 1988; Locker et al., 1991; Macfarlane et al., 2002a). It has been shown that orofacial pain is associated with psychological distress, illness perceptions, and other health symptoms (Macfarlane et al., 2002b,c), which suggests that orofacial pain syndromes may commonly be a manifestation of the process of somatization. Orofacial pain tends to persist (Von Korff et al., 1992); however, it is not clear what factors can predict its persistence. Therefore, by examining a large UK general population sample, we in the present study aimed to contribute further evidence by (a) describing the outcome of orofacial pain after a period of four years, and (b) identifying baseline factors which would predict poor outcome in those with orofacial pain.
Study Design The study was a population-based prospective outcome study. At baseline, participants who had orofacial pain were identified, and pain and potential risk factors were assessed. Four years after the baseline survey, participants were followed up, and those with orofacial pain were identified. 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 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
Participation Rate at Baseline A total of 2504 (62.6%) out of 4000 questionnaires was returned at baseline. Of the remainder, 620 subjects were assumed not to have received the questionnaire, either because they were no longer registered at the address on the electoral roll (n = 469), notification was received from the occupants/post office that the subject had moved (n = 132), they were severely disabled/terminally ill (n = 13), or had died (n = 6). Exclusion of these subjects and two subjects who did not speak English resulted in the adjusted participation rate of 74.1%.
The participation rate was higher in women than in men (P < 0.001), in older people (
Of the subjects who responded, 646 (26%) reported orofacial pain. The majority (64%) were women and lived in affluent areas (55%) (Table 1  ). Only 12% of the participants with orofacial pain at baseline were 25 years or younger (Table 1).
Participation Rate at Follow-up
Description of Outcome after Four Years
Predictors of Long-term Outcome of Orofacial Pain
Psychological factors and health symptoms predicted persistent orofacial pain, with the lowest significantly different from one risk reported for Illness Behavior Questionnaire scale 2 (RR, 1.3; 95% CI, 1.0–1.8) and the highest for widespread body pain (RR, 2.0; 95% CI, 1.4–2.8) (Table 3  ). 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.
The final stepwise model combining both pain characteristics and risk factors identified five factors which explained the persistence of orofacial pain: female gender, older age, medication for orofacial pain, widespread body pain, and General Health Questionnaire score 4–12. Of the 16 participants with orofacial pain at baseline who reported none of these factors, only four (25%) had orofacial pain four years later. This proportion increased with the greater number of risk factors reported (Table 4 ). 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.
This study examined the outcome of orofacial pain after four years of follow-up in a general population. Of those individuals with orofacial pain at baseline, over half reported symptoms at follow-up, a persistence rate that suggests an important long-term burden. This finding is similar to those of other studies which showed that chronic pain tends to persist. For example, another population-based study conducted based on a general medical practice register in the United Kingdom (McBeth et al., 2001) found that 56% of participants with chronic widespread pain still reported symptoms after one year. In a population-based study conducted in Sweden, the three-year persistence rate of chronic widespread pain was 57% (Bergman et al., 2002). In a Finnish working population, of workers with severe knee pain at baseline, 66% still reported severe knee pain after one year (Miranda et al., 2002). In a small clinical population study of fibromyalgia, all patients had persistence of some fibromyalgia symptoms after 10 years (Kennedy and Felson, 1996). A large population study conducted in the United States of America reported that graded chronic pain severity at baseline strongly predicts pain status at three-year follow-up (Von Korff et al., 1992). 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.
The authors are grateful to staff and patients of Lawton House Surgery for their help with the study. The postal costs associated with this project were covered by a grant from Colgate Palmolive Ltd, administered by the Department of Oral Health and Development, University of Manchester. Received for publication September 30, 2003. Revision received June 21, 2004. Accepted for publication June 23, 2004.
Journal of Dental Research, Vol. 83, No. 9,
712-717 (2004)
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ABSTRACT
INTRODUCTION
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