Pain paper 2b: classification of orofacial pain and an update on assessment and diagnosis

Classification of chronic orofacial pain

There have been several attempts to classify chronic orofacial pain (OFP) conditions by pain associations. The most used main categories have either been topographical (odontogenic versus non-odontogenic) and/or chronological (chronic versus acute). Several associations with interest in pain have published classifications: The International Association for the Study of Pain;1 International Headache Society (International Classification of Headache Disorders 2nd edn;2 The American Academy of Orofacial Pain;3 and the Research Diagnostic Criteria for Temporomandibular Disorders.4 As one would expect, critique and suggestions for modification for most of these systems has been published.5

The IASP classification1 categorized orofacial pain (OFP) into ‘Relatively Localized Syndromes of the Head and Neck’ composed of five axes. The IASP system does not, however, fully address the psychosocial aspects of pain, which are required in order to provide a more comprehensive view of the disorder. There is a suggested modification of the classification, which may be applicable to the IASP (the Multiaxial Assessment of Pain [MAP]), as it integrates physical, psychosocial, and behavioural data.

The International Headache Society (IHS)2 has published diagnostic criteria for primary and secondary headaches as well as facial pain. Criteria have also been published by the International Association for the Study of Pain (IASP). The impact of trigeminal pain must not be underestimated. Facial pain can be associated with pathological conditions or disorders related to somatic and neurological structures. There are a wide range of causes of chronic orofacial pain and these have been divided into three broad categories by Hapak et al (1991)5 and Woda et al (2006)6 (Table 1):

The commonest cause of chronic orofacial pain are temporomandibular disorders (TMDs), principally myofascial in nature, and a heterogeneous group including arthritides, arthromyalgia and dysfunctional groups.7

As mechanisms underlying these pains begin to be identified, more accurate classifications, which are mechanism-based, are being used. A major change in mechanism has been that burning mouth syndrome probably has a neuropathic cause, using the newly defined definitions, rather than being a pain resulting from psychological causes. However, we still fall short of an established pathophysiologically based classification system for orofacial pain that would clarify diagnostics and potentially be predictive for management outcome.

Incidence

comparable with other pain conditions in the body, and accounts for between 20 and 25% of chronic pain conditions.8 A 6-month prevalence of facial pain has been reported by between 1%3 and 3%9 of the population. In the study by Locker and Grushka,10 some pain or discomfort in the jaws, oral mucosa or face had been experienced by less than 10% in the previous 4 weeks. In 1980, Bonica11 estimated that 5–7 million Americans suffered from chronic pain in the face and mouth, and 25–45% were affected at some time in their lives. Most population-based studies have shown that women report more facial pain than men,^8,9,10,11 with rates approximately twice as high among women compared to men.10 In clinic populations, the rates for women are even higher. On the other hand, other studies have found no sex difference in the prevalence of orofacial pain. Several studies have also shown variability in the prevalence across age groups. The age distribution of the facial pain population differs from that of the most usual pain conditions. In contrast to chest and back pain, for example, facial pain has been suggested to be less prevalent in older age. Consequences include interruption with daily social function, such as eating, drinking, speaking, kissing, applying make-up, shaving and sleeping. Burning mouth syndrome has been reported to cause significant psychological impact in 70% of patients with temporomandibular joint (TMJ) pain; 29% of patients report high disability resulting in unemployment.7

Assessment and diagnosis of orofacial pain

Often, patients with OFP will be seen by a clinician who has experience in one aspect of orofacial pain. Dentists will explore dental pain, an ENT surgeon will assess for sinus and ear-related pain, etc. Consulting a patient in pain requires specific skills and excellent communication. Patients are often anxious visiting the dentist without pain; whilst in pain their anxiety levels are potentially increased, related to the imminent treatment necessary to treat the cause of their pain. Communication is key to eliciting an appropriate history from your patient and the clinician must be a good listener. The patient must also be able to communicate clearly and this is often difficult, for example, children, intellectual disability in the general population (2.5%), cerebral palsy, dementia in 8% of people over 65 years, brain damage (5–1.9 million head injuries per year with 10% of these being serious).12 These people are all even more vulnerable to pain because of their inability to communicate how they feel.

In order to provide each patient with the most suitable treatment plan to address individual needs, it is essential to discover as much information as possible about each patient's experience, expectations, health and quality of existing dentures. Ideally, a multidisciplinary team should assess complex chronic pain patients including: dentists, neurologists, clinical psychologists, psychiatrists, neurosurgeons and pain management consultants.

Patient presentation with persistent pain is often complex and may be driven by many factors. Patients may be fit and well or have significant co-morbidity, including psychological, medical history complexities, or have difficulty managing their anxieties and fears. Fear and anxiety will increase the pain experience and may require adjunctive therapy, including behavioural and medical techniques. As pain is multi-dimensional, many aspects of the impact of pain on the patient must be assessed. The biopsychosocial model illustrates the many environmental, phenotypic and psychological factors (Figure 1).

These factors must be taken into account when consulting the pain patient. The attentive, listening clinician will build a rapport with his/her patient rapidly and the ensuing trust will allow the patient to confide in the attending clinician, providing invaluable information about the ongoing complaint. Managing patients' expectations is paramount and often a cure is not possible but management is; providing the patient with a clear understanding of what is taking place with realistic goals is essential.

Measuring pain

Measuring pain is near impossible. The pain experience is an entirely individual response. No other person can derive your own experience of pain because you alone experience it and, owing to its complexity, conveying your total pain experience to others is impossible. Unless your clinician is equipped with Dr Spock's (from Starship Enterprise not paediatrics) ability to key into your experience using bi-temporal palpation, sharing your pain experience will depend upon your clinician's talent for listening and empathizing which may, in part, allow him/her to begin to understand your pain. We attempt to gain an idea of the affective component of your pain experience using questionnaires for psychometrics and we use questionnaires to assess your functionality, disability and behaviour. Scoring pain using a Lickhert scale is standard practice but it massively oversimplifies the complex pain experience.

A pain diary may provide both clinician and patient with an extremely useful adjunct to the initial pain history, particularly by clarifying the response of the pain to various medications, avoidance strategies taken by the patient, and identifying factors that exacerbate the pain. Daily changes in the pain are important, for example:

Psychological assessment of the pain patient (Table 5)

In the introductory section to this series the significant component of the affective and emotional role in pain perception, behaviour and suffering is highlighted. As pragmatic clinicians we tend to focus on ‘mechanical/medical’ interventions to prevent the nociceptive pain and forget the ‘holistic’ management of pain. With simple acute inflammatory conditions that can be simply managed with a swift and effective surgical intervention, less understanding of the affective burden is required. However, in chronic pain the emotional components of persistent pain, its social, functional and resultant psychological sequelae, cannot be underestimated.20^,29 The biopsychosocial model of pain (Figure 1) emphasizes the complexity of managing pain patients. Many authors have made recommendations regarding the preferred psychological assessment of the pain patient.^{30,31,32,33,34,35} Our local orofacial pain team, which includes liaison psychiatrist, clinical psychologist, health psychologist, dental clinicians, neurosurgeon, neurologist and pain management consultant, use the questionnaires in Table 5. Using these questionnaires we are able to elicit anxiety and depression that may be contributory to the patient's pain condition. We can identify his/her ability to cope and how impactful the pain is in relation to daily function. Red flags including self-harming tendency and suicidal ideation can also be identified early on, precipitating an expeditious referral to the psychiatrist. Overall, the patients are extremely co-operative with completing these questionnaires and the data collected is undoubtedly facilitating the development of tailored cognitive behavioural techniques for specific orofacial pain conditions.

Summary

Most importantly, the clinician must keep a broad perspective of the patient's presentation and complaint. Systemic diseases, psychological and environmental factors all play a potential role in the patient's pain experience and thus must be considered in order to provide effective pain alleviation and education. The subsequent papers provide an update on the management of acute and specific chronic trigeminal pain conditions. Pain management procedures, including local anaesthesia and the management of anxiolysis (behavioural techniques and medical techniques – sedation), are not included in this series.