Distribution of depression, somatization and pain-related impairment in patients with chronic temporomandibular disorders

Abstract Objective the aim of this study was to describe the frequency of psychosocial diagnoses in a large sample of patients attending a tertiary clinic for treatment of temporomandibular disorders (TMD). Material and Methods six hundred and ninety-one patients who sought treatment for pain-related TMD were selected. Chronic pain-related disability (Graded Chronic Pain Scale, GCPS), depression [Symptoms Checklist-90 (SCL-90) scale for depression, DEP] and somatization levels (SCL-90 scale for non-specific physical symptoms, SOM) were evaluated through the Research Diagnostic Criteria for TMD (RDC/TMD) Axis II psychosocial assessment; TMD diagnoses were based on the Axis I criteria. Results the majority of patients presented a low disability or no disability at all, with only a small portion of individuals showing a severely limiting, high disability pain-related impairment (4.3%). On the other hand, abnormal scores of depression and somatization were high, with almost half of the individuals having moderate-to-severe levels of depression and three-fourths presenting moderate-to-severe levels of somatization. The prevalence of high pain-related disability (GCPS grades III or IV), severe/moderate depression and somatization was 14.3%, 44% and 74.1% respectively. Gender differences in scores of SCL-DEP (p=0.031) and SCL-SOM (p=0.001) scales were signficant, with females presenting the highest percentage of abnormal values. Conclusion patients with TMD frequently present an emotional profile with low disability, high intensity pain-related impairment, and high to moderate levels of somatization and depression. Therefore, given the importance of psychosocial issues at the prognostic level, it is recommended that clinical trials on TMD treatment include an evaluation of patients’ psychosocial profiles.


Introduction
Several studies have reported that patients with chronic pain conditions show high psychosocial impairment compared with pain-free control groups. 1,2 These psychosocial variables are associated with poorer pain-related adjustment among patients with chronic pain. 3 Similar results have also been reported for patients with painful temporomandibular disorders (TMD) (i.e., myofascial pain, arthralgia, arthritis), who showed higher psychosocial impairment than TMD-free individuals. 4,5 Based on such observations, theories on the etiology of TMDs and its implications for treatment have progressively embraced the importance of a comprehensive biological and psychosocial assessment 6 and TMDs are now viewed as a complex disorder resulting from an interplay of causes, including multiple genetic and environmental domains. 7 Psychological impairment is associated with greater severity and persistence of TMD-related clinical symptoms, 7 which affect approximately 10% of the population, with a higher prevalence in females. 8 T h e R e s e a r c h D i a g n o s t i c C r i t e r i a f o r Temporomandibular Disorders (RDC/TMD) Axis II 9 was specifically designed for a thorough psychosocial assessment, allowing evaluation of the severity of chronic pain and the levels of depression and somatization in TMD patients. The revised and updated version, now called Diagnostic Criteria for TMD (DC/ TMD), 10 13 The absence of correlation between Axis I, i.e. the diagnoses of TMD physical symptoms, and Axis II, i.e. the level of psychological and pain-related impairment, has been reported. 14 Moreover, treatment-seeking behavior seems to be the discriminant factor to differentiate patient and non-patient populations, and psychosocial factors emerged as the main predictor of treatment outcome. 15 Considering these drawbacks, the paucity of epidemiological data on Axis II is still evident in the TMD literature. Therefore, the aim of this study was to describe the frequency of psychosocial diagnoses in a large sample of patients attending a tertiary TMD clinic to provide an epidemiological basis for future comparisons.

Assessment instruments
Complete examination was carried out according to the Italian version of the RDC/TMD protocol (RDC/ TMD Consortium Network). Psychosocial status was assessed by the Axis II questionnaire, which contains specific items for the appraisal of chronic pain severity and of subjective signs and symptoms for levels of depression and somatization. 9 The Graded Chronic Pain Scale (GCPS) 16 (Table 3).
Likewise, females presented the highest frequency of severe impairment in the SCL-DEP and SCL-SOM scales, with 42.6% and 53.4% respectively (Table 4).

Discussion
The importance of assessing psychosocial factors in TMD patients has been recognized in the literature, which showed an association between TMD pain and psychological symptoms including depression, somatization, and anxiety. 6,14 To address this issue, the      findings (i.e., Axis II) with the latter, rather than the former, being the key issue to predict the treatment outcome. 14,15 Thus, approaching TMD epidemiology without taking into account the Axis II limits the construct of the so-called biopsychosocial model of pain. 11 Therefore, this large-sample investigation reports Axis II findings in a population of TMD patients attending a tertiary clinic to provide a framework for clinicians who could expect patients with different ratings of psychosocial impairment, regardless of the Axis I diagnoses.
In this investigation, based on GCPS scores, the frequencies of the most severe degrees of painrelated impairment were 10% for grade III and 4.3% for grade IV. Available data on the different GCPS categories reported prevalence of 3.1% and 6.3% of high intensity, severely and moderately limiting pain respectively, 18 which is similar to the findings of this study. This investigation is also in line with other three studies reporting a range of 13% to 21.8% for the two most severe GCPS ratings. 5 The importance of assessing the levels of pain intensity and pain-related disability evaluated by the GCPS lies in its influence on the clinical decision-making process, i.e. knowing or not such profile is emerging as a factor that affects the prognosis of TMD symptoms.
In short, it can be suggested that patients with severe impairment are the worst treatment responders, while those with low impairment seem to have benefit even from "simple" cognitive-behavioral therapy regimen and may take advantage of the positive natural variation of symptoms. 14,15,19 In addition, the GCPS has been used to identify groups of patients that may benefit more from cognitive-behavioral approaches. 20 Thus, it is quite surprising that the number of research on pain-related impairment in TMD patients is not relevant; also, the increase in the diffusion of GCPS in both research and clinical settings is strongly recommended to aid the selection of an appropriate treatment protocol including tailored strategies to address pain-related impairment. 21 Lack of Axis II records and/or inappropriate interpretation of Axis II findings is a shortcoming that negatively affects the definition of management strategies in clinical settings.
As for the SCL-90R scores, moderate to severe levels of depression and somatization were detected in 44% and 74.1% of patients, respectively. These findings are similar to available data in which the prevalence of depression and somatization was 49% and 69% respectively; 4  This investigation has some shortcomings that could be addressed in future studies. The main limitation is the absence of information on the Axis I diagnosis, which might have given a more complete clinical picture. On the other hand, the absence of correlation with the psychosocial findings has already been shown, 14 and Axis II is emerging as the most important outcome predictor for treatment purposes. 15,21 As a further note, the inclusion of TMD-free control groups could impact the relative importance of psychosocial impairment in TMD patients with respect to the general population, but it should be remarked that previous case-control studies support a higher Axis II impairment in TMD patients. 4 Moreover, despite all aforementioned statements about the TMDpsyche relationship and usefulness of the RDC/TMD Axis II scales for the evaluation of depression and somatization symptoms, 26 it must be remarked that they provide an assessment of clinical characteristics and are not diagnostic of any psychopathology. Based on that, the inclusion of psychologists in the team of caregivers is recommended when such screening tools identify severe Axis II symptoms. Finally, future investigations using the DC-TMD and the additional Axis II tools will help to assess the psychosocial profile of TMD patients in a more comprehensive way.
Thus, to our knowledge, this investigation presented the largest Axis II data collection in a TMD population for future comparison. Methodological issues concerning the size and representativeness (e.g. type of TMD, pain duration) of the study population should be considered for refinement and comparison with future investigations.

Conclusions
Based on our findings, it can be concluded that patients with TMD frequently present an emotional profile with low disability, high intensity pain-related impairment and with high to moderate levels of somatization and depression. Given the importance of psychosocial issues at the prognostic level, it is recommended that these data are taken as reference standpoint for future comparisons and that clinical trials on TMD treatment include an evaluation of patients' psychosocial profiles in order to identify pain phenotypes related to the TMD manifestation.