Introduction
Accurate diagnosis of orofacial pain (OFP) is essential for appropriate patient management in primary and secondary care. Acquisition of a detailed pain history and examination directs diagnoses and treatment [
1]. However, diagnosis of OFP is complex. Certain types of OFP are musculoskeletal in origin, such as temporomandibular disorders (TMD), others are neuropathic, such as trigeminal neuralgia (TN) and nerve injury-post dental extraction, whereas some have an unknown aetiology, such as chronic (persistent) idiopathic facial pain (CIFP). Mixed pain syndromes may also exist, where, rather than a binary distinction, pain may exist on a continuum of ‘more or less neuropathic’ [
2,
3]. Due to a limited understanding of the pathophysiology of these processes, and the possibility of multiple OFP diagnoses occurring within the same patient, misdiagnosis and inappropriate referral of these patients is common, particularly for non-specialist clinicians [
4,
5]. The management of musculoskeletal compared to neuropathic origin varies. For example, though commonly prescribed in primary and secondary care, non-steroidal anti-inflammatory medications are not recommended for neuropathic pain [
6]. Moreover, the management of neuropathic pain is challenging, as patients are frequently unresponsive to drug treatment [
7]. Earlier recognition and distinction of the aetiology of OFP in patients is needed, particularly due to the substantial patient burden and interference with daily living that some diagnoses may have [
8].
Patient-completed screening questionnaires may supplement the recognition and clinical diagnosis of OFP in a variety of settings. These are paper-based or electronic tools that are easily administered to patients. In differentiating between common dental conditions and unknown OFP diagnoses [
9], screening questionnaires may be useful for the earlier triaging of OFP patients to appropriate secondary or tertiary care pathways. However, it is important that these tools are validated for use in different settings, including primary or secondary care and epidemiological surveys. Such screening questionnaires may also be available to patients to complete and score over the internet, with no input from health care professionals, which adds to the importance of determining if they can accurately recognise different OFP diagnoses.
One such tool developed in 2006, the painDETECT screening questionnaire (PD-Q), uses a scoring method between − 1 and 38 to estimate the likelihood of a neuropathic pain component in patients. The PD-Q was originally designed to identify neuropathic components in back pain [
10]. Since its conception, the PD-Q has been validated and translated into multiple languages, it is easy for patients to use, and has been shown to identify neuropathic pain components in different contexts, including lower back pain, arthritis, fibromyalgia, thoracotomy and malignancy [
11]. Compared to other screening tools for neuropathic pain, the PD-Q does not require clinical examination, inquires about pain evoked by mild pressure and heat or cold [
12] and thus has the potential to be used as a rapid pre-consultation tool to differentiate between aetiologies of OFP. To date, the PD-Q has been tested in populations of patients with specific OFP diagnoses. Elias and colleagues found that 34% of patients with post-traumatic trigeminal nerve injury at their centre obtained a PD-Q score of at least 19 [
13]. More recently, Heo and colleagues applied the PD-Q to patients with burning mouth syndrome (BMS), and found a low sensitivity and high specificity for the identification of neuropathic pain components in this population [
14]. Testing the PD-Q across a broad range of facial pain diagnoses is required to determine whether this tool would have utility as a screening tool for neuropathic pain in OFP. Our centre receives a heterogeneous group of patients with OFP [
5], providing an opportunity to assess the PD-Q in a secondary care setting. The aim of this study was to determine the utility of the PD-Q to detect neuropathic pain in a hospital-based cohort of patients with OFP.
Discussion
This prospective study tested the accuracy of the PD-Q in identifying neuropathic pain components in a hospital-based cohort, with a broad range of orofacial pain diagnoses. At the PD-Q score above which neuropathic components are likely, the PD-Q had a low sensitivity and high specificity. Conversely, at the lower PD-Q cut-off, the PD-Q has a modest sensitivity and specificity. The PPVs and NPVs were modest at both cut-offs, indicating a reasonable likelihood that patients with a score above 19 would have a neuropathic pain component, and that patients with a score below 12 would not. PD-Q scores were significantly different between clear neuropathic OFP diagnoses, such as TN or TNP, compared to non-neuropathic diagnoses, such as TMD, whereas mixed diagnoses such as CIFP were more ambiguous. Together, these data suggest that the PD-Q identifies neuropathic components when clear-cut, but unsurprisingly, performs less well in patients with a complex, mixed diagnosis, particularly when multiple diagnoses are present.
Previous studies have examined the utility of the PD-Q for OFP diagnoses in tertiary centres, and suggest the PD-Q may not be an appropriate tool in this context. Elias and colleagues found that only 34% of patients with post-traumatic trigeminal nerve injury obtained a PD-Q score of at least 19 [
13]. Heo and colleagues applied the PD-Q to patients with BMS, and found a low sensitivity (16.7%) and high specificity (97.4%) at a cut-off of 19 [
14]. These studies, with smaller sample sizes, include patients with predominantly neuropathic pain, and their findings may reflect the low sensitivity of the PD-Q at the higher cut-off value in the present study. In contrast, our ROC analysis suggested that the PD-Q has potential for recognition of neuropathic pain in this hospital-based cohort, likely because our patient population is more heterogeneous and representative of secondary care.
Unlike other questionnaires for neuropathic pain, the PD-Q does not involve clinical examination. Such examination, including changes in sensory perception, is critical for making a diagnosis of a neuropathic pain [
12]. The PD-Q was originally designed to identify neuropathic components in lower back pain [
10]. Though response rates in this study reflect the ease of completing the questionnaire, the design of the PD-Q makes it difficult for patients to highlight and draw areas where pain predominates and radiates to, particularly considering as the size of the head is very small in the figure within the PD-Q. Questions in the PD-Q referring to possible pain triggers do not account for specific face pain triggers such as washing the face, showering compared to bathing, or the cold wind; all of which are clues towards orofacial pain of a neuropathic aetiology, such as classic TN [
21].
Despite the strengths of this study, including its prospective nature, blinding of the clinician to the questionnaire results and the confirmation of the reference standard of clinical diagnosis by an independent clinician, our data should be interpreted with caution. Firstly, the study was conducted in a secondary care centre, receiving population of orofacial pain patients not representative of primary care or non-specialist settings. Data previously published from this centre indicated that up to 46% of the patients seen have a diagnosis of TMD [
5], whereas its estimated prevalence in the general population is between 2 and 6% in developed countries [
22]. Given this prevalence, the rarity of conditions such as TMD and TN would make a prospective study in primary care extremely challenging. Another difficulty in translating these results to primary care is the possibility of changes to the way the questionnaire is filled out in different settings. In different settings, patients may rate their pain variably, dependent on their expectations and desired outcomes of their consultation. Other factors differ between centres, such as the person administering the measure, be they clinician, family member or study investigator. Moreover, only a small number of patients with acute dental pain were recruited, which contrasts with primary dental care in which acute dental pain is predominant. However, the inclusion of these patients demonstrated that acute dental pain is not classified as neuropathic, and demonstrate that patients who score highly in primary dental care should be referred to a specialist centre for appropriate management of neuropathic pain. A second limitation is the difficulty in accommodating for the large proportion of patients in each group with a secondary diagnosis. This is representative of the complexity of orofacial pain presentations, and considerably influences the ability of the PD-Q to accurately identify OFP aetiology, independent of other patient factors, but likely influences non-adjusted analyses. To accommodate for this, study clinicians made a primary diagnosis based on patient history and examination, to determine the predominant type of pain. The study is further limited by characteristics not recorded, such as the pain intensity or educational level of patients, both of which could influence PD-Q scores. Though patients were recruited consecutively over individual study periods, the nature of the study, namely the periods of time during which patients were not recruited due to absence of postgraduate students, may have introduced selection bias to the sample. Re-test validity was not included in this study. Finally, the clinician confirming the diagnosis, though independent, was not blinded to diagnosis made at first consultation, and may be biased by this information or by treatment response. The time between diagnosis made at first consultation and independent confirmation was not recorded.
The accuracy of the PD-Q is only one of the considerations when determining a screening tool for OFP. The PD-Q appears a valid tool, in its effectiveness in distinguishing neuropathic from non-neuropathic pain in other contexts [
11], the continuous score of the PD-Q reflecting the spectrum of neuropathic pain presentations [
3] and its availability and validation in different languages. What has not been compared is the ultimate treatment and outcome of patients and how these relate to the initial PD-Q scores, which could be considered its criterion validity. Moreover, the reliability of the PD-Q in patients with OFP needs to be ascertained prior to its implementation in practice. Preliminary data at our centre indicates a strong concordance in PD-Q score before and after consultation with a facial pain clinician, but larger sample sizes are needed to validate this. The utility and performance of the PD-Q could also be compared to other screening tools for neuropathic pain [
12], and more specific screening tools for OFP diagnoses, such as those available for TMD and TN [
23,
24]. Finally, the differences between settings prompt a revalidation of the PD-Q in primary care [
25], given the considerably lower prevalence of specific OFP diagnoses in general clinical and dental practice.
Conclusions
Patient-completed screening tools, such the PD-Q, have promise in both primary care and hospital practice, given their ease of use, high completion rate and the potential to aid the triaging of patients with OFP prior to consultation. Such tools may help to identify patients in primary care who need a specialist referral, those in dentistry who have a non-odontogenic origin of their pain or may help to inform clinicians as to the aetiology of pain to make earlier decisions about management and therapy. However, the PD-Q performed modestly in our centre given the complexity of presentation and as many patients have more than one co-existing diagnosis. Prior to clinical and further research applications, the PD-Q must be adapted and revalidated for orofacial pain patients, and separately in primary care, where orofacial pain is considerably less common. Ultimately, either patient-completed screening tools should only be implemented within settings they were designed, or pre-existing general screening tools needs to be optimised in different settings to reflect the variety of clinical situations for which such tools may be applicable.
Acknowledgements
The authors would like to thank the UCL AcaMedics scheme, for linking DJ to the Orofacial Pain Unit, and Sarah Tonks and Abdouldaim Ukwas; postgraduate students who contributed to the ethics approval and PD-Q data collection.