Classification of Orofacial Pain

Transcription

1 Classification of Orofacial Pain Gary D. Klasser, Jean-Paul Goulet, Antoon De Laat, and Daniele Manfredini Abstract Designing a classification system for any disease entity, let alone orofacial pain and more specifically for temporomandibular disorders, is quite the task. Unfortunately, this is made even more difficult due to the many conditions, both physical and psychosocial, that must be accounted for when undertaking this challenge for these aforementioned entities. In order to appreciate the utility of classification systems, it is first necessary to gain an understanding and comprehension as to their importance and how it may be optimally operationalized for both clinical and research activities. Other considerations that must be taken into account are G.D. Klasser (*) Department of Diagnostic Sciences, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, LA, USA gklass@lsuhsc.edu J.-P. Goulet Faculté de Médecine dentaire, Université Laval, Québec, QC, Canada jean-paul.goulet@fmd.ulaval.ca A. De Laat Department of Oral Health Sciences, K.U. Leuven, Leuven, Belgium Department of Dentistry, University Hospitals Leuven, Leuven, Belgium antoon.delaat@uzleuven.be D. Manfredini School of Dentistry, University of Padova, Padova, Italy daniele.manfredini@tin.it # Springer International Publishing AG 2016 C.S. Farah et al. (eds.), Contemporary Oral Medicine, DOI / _29-1 past and present classification systems that have been espoused by various organizations. Each of these needs to be carefully evaluated within a framework of their inherent advantages while exposing their limitations. These previously established classification systems must then be integrated with newly proposed expanded upon or modified systems as a result of recent findings from contemporary evidenced-based scientific literature. Hopefully, this will lead to an ideal classification system whereby other factors such as genetics and neurobiological process can be reviewed for inclusion in this expanded schema. Additionally, adopting newer approaches, such as following ontological principles, will result in a more thorough and comprehensive classification system which ultimately will assist the clinician in providing improved diagnosis, the researcher in studying more homogenous groups, and the patient in receiving more directed and individualized interventions. Keywords Orofacial pain Temporomandibular disorders Classification systems Taxonomy Ontology 1

2 2 G.D. Klasser et al. Contents Introduction... 2 Development Strategies Towards a Classification System... 3 Current Orofacial Pain Classification Systems (General)... 4 International Association for the Study of Pain International Headache Society... 5 American Academy of Craniofacial Pain... 8 Current TMD Classification Systems... 9 RDC-TMD to DC-TMD and the Expanded TMD Taxonomy... 9 Proposed Classification Systems Classification of Chronic Idiopathic Orofacial Pain: Woda et al. (2005) Classification of TMJ Disorders: Stegenga (2010) Classification Profile of TMD Patients: Machada et al. (2012) Classification of Orofacial Pains: Okeson (2014) Psychosocial Subtyping of TMD Patients: Suvinen et al. (2005) Advantages and Limitations Futures Classification Systems Axis III: Genetics Axis IV: Neurobiological Taxonomy and Ontology: A New Approach for Classification Systems Conclusions Cross-References References Introduction A classification is defined as a systematic arrangement in groups or categories according to established criteria (Merriam-Webster 2015). A classification allows the definition of specific entities according to specific characteristics. In general medicine and thus for orofacial pain (OFP), the characteristics of such an ideal diagnostic system could be derived from the etiology, pathophysiology, diagnosis, and/or management of a specific disease or disorder. For the clinician, a correct definition and classification is important to name and classify the specific disease entity since it will assist in planning the management and in discussing the prognosis with the patient. For the patient, receiving a clear and definitive diagnosis allows for a better understanding and acceptance of aspects related to etiology and pathophysiology, promotes inclusion to a specific group instead of feeling in the dark, and facilitates acceptance of the different steps of management. For researchers, it is imperative to have homogenous groups when designing clinical studies, and for communication among each other. An ideal classification system would need to satisfy several requirements (Fillingim et al. 2014): it should be exhaustive (comprising all clinical diseases or disorders belonging to the field of interest), biologically plausible (the symptoms and signs should match with known biological processes), mutually exclusive (there should be no overlap between disease entities because of common symptoms), clinically useful (so that it can be used to help in treatment and prognosis), reliable (consistently applicable in a reproducible way between clinicians and over time), and simple for practical use. Most of the current classification systems regarding OFP suffer from deficits in at least one of these qualities. In addition, since several independent groups of clinicians (originating from different disciplines) try to build a classification, several disease entities have been defined differently, and this is further complicated when attempts are made to implement new insights resulting from ongoing research (Woda and De Laat 2014). As pointed out further in this chapter, there is no consensus (yet) regarding a universal and unique classification of OFP. Such a classification requests the support of a majority of clinicians and researchers and would ideally also implement newer insights regarding the individual differences at a patient level to an otherwise identical diagnosis. The most recent attempt to start this process is made by the ACTTION-AAPT approach (Fillingim et al. 2014) where in line with the biopsychosocial model for pain the importance of a multiaxial evaluation and characterization is advocated.

3 Classification of Orofacial Pain 3 Development Strategies Towards a Classification System Over time, several strategies have been developed in order to build a classification system for OFP, all with their advantages and limitations (Woda and De Laat 2014). This section will attempt to provide an overview of these ongoing efforts. Traditionally, the oldest attempts to classify diseases or disorders were based upon expert opinion, and an authority-based consensus, mostly focused on particular organ-systems or pathophysiological processes. Several societies and medical subdisciplines created task forces of experts to share their knowledge and experience and develop a restricted set of criteria to denominate a set of particular diagnoses. These clinical entities were, to the extent possible, organized in a hierarchical way so as to create the classification. Examples of this approach are the classification systems of the International Headache Society (IHS) (Headache Classification Committee of the International Headache Society 2013), the International Association for the Study of Pain (IASP) (Merskey and Bogduk 1994), and the Research Diagnostic Criteria for Temporomandibular Disorders (RDC-TMD) (Dworkin and LeResche 1992). Using diagnostic criteria can facilitate the search for homogeneous groups that would be beneficial for both clinicians and researchers. However, certain inherent problems arise whereby a selected set of signs and symptoms is used to characterize an already selected group as this does not prevent the overlapping of disease entities. In addition, if a group of patients is selected on the basis of the criteria, it is not known whether they all belong to a single disease or that it is a sample of (partially) overlapping disease entities. The specific criteria in such a diagnostic system, however, can be evaluated and tested for their reliability, specificity, and sensitivity, and this has been done (e.g., RDC-TMD) resulting in refinement and adjustment of some of the criteria (Schiffman et al. 2010a). Unfortunately, this method has also the limitation that circular reasoning is possible since the validation is done on the basis of an a priori set of inclusion criteria. In contrast to the method of diagnostic criteria, the methodology of cluster analysis does not depart from an already existing disease entity, organ system, or pathophysiological process, but allows for statistical grouping within a dataset of signs and symptoms (Woda et al. 2005). This technique to classify groups of patients surpasses the organ system/specific tissue involved in the pain and might better approach a mechanismbased classification. In a next step, diagnostic criteria for each cluster are necessary, which in turn need to be tested for validity, specificity, and sensitivity. Recently, a more theoretical reflection on the basis of ontological principles has been advocated (further discussion presented in section Taxonomy and Ontology: A New Approach for Classification Systems) (Nixdorf et al. 2012). Applying this theoretical approach helps in the development of clear taxonomy, irrespective of new developments in etiological or pathophysiological issues. Ideally, this methodology would be applied to the disease entities emerging from previous cluster analysis. In order to address the existing confusion created by the many pain classifications, to implement also the new developments regarding the paradigm used to explain the genesis and experience of pain (the biopsychosocial model) as well as the call for a mechanism-based approach to diagnosis, a large-scale multidisciplinary publicprivate partnership was established (Fillingim et al. 2014). The ultimate goal of the ACTTION- AAPT project is to satisfy the urgent need to develop a systematic, standardized, and evidence-based pain classification system applicable to all common chronic pain syndromes that also takes into account the biopsychosocial mechanisms. Such classification, integrating neurobiological and biopsychosocial mechanisms, would improve management selection and patient outcome, would facilitate communication between clinicians and researchers, and would be of benefit in research design and in education.

4 4 G.D. Klasser et al. Current Orofacial Pain Classification Systems (General) International Association for the Study of Pain Thirty years ago the IASP became the first international organization to introduce a provisional compilation of chronic pain syndromes that can affect any part of the body. The Subcommittee on Taxonomy recognized this as the beginning of a continuous review process that would address gaps, inaccuracies, and inconsistencies raised by anyone with expertise in the field of pain for future modifications and improvements. While this first edition provided an overall acceptable classification of relevant chronic pain syndromes to many, a number of changes were introduced in the second iteration published in 1994 and this was followed by more recent updates in 2011 and 2012 (Merskey and Bogduk 1994). New conditions were added, names were changed, and terms not describing specific syndromes were rejected. In spite of significant advances in classifying many conditions, very few changes were introduced to the head and face pain syndromes. This IASP classification system adopted an arrangement of pain syndromes in nine major categories regrouped either under generalized conditions that can affect various parts of the body or more localized conditions found at specific body sites. More than 400 pain syndromes are listed in 33 subcategories. The taxonomy includes a systematic description of pain syndromes with specific emphasis placed on the case definition and main pain features. In addition, the IASP developed a scheme enabling the codification of each diagnosis in a more detailed manner on the basis of five axes that include: (1) body region, (2) systems involved, (3) temporal characteristic of pain in terms of pattern of occurrence, (4) patient s statement of intensity coupled with time since onset of the pain, and (5) etiology. Clinical phenotypes of OFP-related disorders are found under the major category Relatively localized syndromes of the head and neck that is further divided in seven subcategories. Almost two-third of the 66 pain-related syndromes listed represent an OFP condition and depending on the source and structure involved these are classified into one of the five subcategories presented in Table 1. While the purpose of the IASP is to offer a compilation of chronic pain syndromes, a few acute conditions are interwoven into the classification scheme with the purpose of pointing out contrast with other chronic pain entities. This is particularly true for Group IV Lesions of the ear, nose, and oral cavity that includes conditions like maxillary sinusitis, odontalgia toothache 1, 2, and 3, respectively, due to dentino-enamel defects, pulpitis, periapical periodontitis or abscess, and dry socket for which the usual course will rarely exceed a week or so. More recently, the IASP interacting with the World Organization (WHO) established a Task Force to develop a new pragmatic classification of chronic pain after noticing the discrepancies between the actual epidemiology of chronic pain and the diagnostic codes included in the current version of the International Classification of Diseases (ICD) of the WHO. The aim is to simplify and better standardize the categorization of chronic pain conditions so it could be used in primary care as well in clinical settings for specialized pain management, while also fitting into the general framework of the upcoming 11th revision of the ICD. The new ICD scheme categorizes chronic pain into seven (7) groups of disorders with priority given first to pain etiology, then to underlying pathophysiological mechanisms, and lastly to body sites. Moreover, the principle of multiple parenting that allows the same diagnosis to be assigned to more than one category is applied when needed. The seven groups of chronic pain disorders serving as an umbrella are: (1) chronic primary pain, (2) chronic cancer pain, (3) chronic posttraumatic and postsurgical pain, (4) chronic neuropathic pain, (5) chronic headache and orofacial pain, (6) chronic visceral pain, and (7) chronic musculoskeletal pain (Treede et al. 2015).

5 Classification of Orofacial Pain 5 Table 1 IASP subcategories of Relatively localized syndromes of the head and neck that include orofacial painrelated disorders with the list of conditions for Group III and IV (Merskey and Bogduk 1994) Relatively localized syndromes of the head and neck Group II: Neuralgia of the head and face Group III: Craniofacial pain of musculoskeletal origin 1. Acute tension headache 2. Tension headache: Chronic form (Scalp muscle contraction headache) 3. Temporomandibular pain and dysfunction syndrome (also called Temporomandibular disorder) 4. Osteoarthritis of the temporomandibular joint 5. Rheumatoid arthritis of the temporomandibular joint 6. Dystonic disorders, facial dyskinesia 7. Crushing injury of head and face Group IV: Lesions of the ear, nose, and oral cavity 1. Maxillary sinusitis 2. Odontalgia: Toothache 1. Due to dentino-enamel defects 3. Odontalgia: Toothache 2. Pulpitis 4. Odontalgia: Toothache 3. Periapical periodontitis and abscess 5. Odontalgia: Toothache 4. Tooth pain not associated with lesion (Atypical odontalgia) 6. Glossodynia and sore mouth (aka Burning tongue or Oral dysesthesia) 7. Cracked tooth syndrome 8. Dry socket 9. Gingival disease, Inflammatory 10. Toothache, cause unknown 11. Diseases of the jaw, inflammatory conditions 12. Other and unspecified pain in the jaw 13. Frostbite of face Group V: Primary headache syndromes, vascular disorders, and cerebrospinal fluid syndromes Group VI: Pain of psychological origin in the head, face, and neck Advantages and limitations: The classification of chronic pain in the ICD is in the process of being overseen by peer review. As for the current IASP classification, with its five axes, it offers the most exhaustive and elaborate system for coding chronic pain cases. As many as ten different entries are possible per diagnosis within each axis, however, the coding is not necessarily a user friendly task. The IASP places emphasis on the description of pain syndromes and diagnostic criteria are provided only when possible and in various formats. While they may have face and content validity there are no data yet on their accuracy. Within the context of OFP-related disorders, the IASP classification has very limited value for the diagnosis of temporomandibular disorders (TMDs). Beside the arthritides, all the other conditions are collapsed under the old denomination Temporomandibular Pain and Dysfunction Syndrome. The reluctance of the IASP to adopt and integrate the classification criteria of other organizations with special interest for pain diagnosis in specific body parts has significant drawbacks. For categories like primary headaches and neuralgias of the head and neck, similar conditions can have different names and diagnostic criteria. In addition, there are conditions for which no counterpart exists in the IASP scheme. Even though the IASP provides a crosswalk to the IHS coding system for headaches, it nevertheless creates some confusion. It is hard to dismiss any of the current five axes of the IASP classification, but the addition of one giving due consideration to the biopsychosocial and behavioral factors of the patient s pain experience would certainly be useful (Turk and Rudy 1987; Turk 1990; Fillingim et al. 2014). We know that regardless of the biomedical diagnosis these may influence treatment outcomes in subgroups of chronic pain patients (Turk 1990). International Headache Society Not long after the IASP created their classification system, the IHS published the International Classification of Headache Disorders (ICHD) in It was first updated in 2004 and more recently in 2013 (ICHD-3) based on changes supported by quality published evidence (Headache Classification Committee of the International Headache Society 2013). The IHS offers a compilation of all headache-related disorders and painful craniofacial neuropathies along with other facial pains in a three part classification system. Part I and Part II are, respectively, devoted to primary and secondary headaches and composed of 12 major categories. Part III is a repertory of painful cranial neuropathies, other facial pains, and headaches

6 6 G.D. Klasser et al. Table 2 Classification system of the International Headache Society for headaches and facial pains (ICHD-3) (Headache Classification Committee of the International Headache Society 2013) Part one: Primary headaches 1. Migraine 2. Tension-type headache 3. Trigeminal autonomic cephalalgias 4. Other primary headache disorders Part two: Secondary headaches 5. Headache attributed to trauma or injury to the head and/or neck 6. Headache attributed to cranial or cervical vascular disorder 7. Headache attributed to nonvascular intracranial disorder 8. Headache attributed to a substance or its withdrawal 9. Headache attributed to infection 10. Headache attributed to disorder of homeostasis 11. Headache or facial pain attributed to disorder of the cranium, neck, eyes, ears, nose, sinuses, teeth, mouth, or other facial or cervical structure 12. Headache attributed to psychiatric disorder Part three: Painful cranial neuropathies, other pains and other headaches 13. Painful cranial neuropathies and other facial pains 14. Other headache disorders arranged in two distinctive categories, one for the primary painful craniofacial neuralgias and related facial pain and the other for headaches not elsewhere classified or unspecified (Table 2). The ICHD is primarily a hierarchical classification system for headaches with welloperationalized diagnostic criteria. Interestingly, it allows the clinician to decide how detailed the diagnosis should be within each of the 12 major headache categories when looking through the subtypes of headache disorders. Thus, the coding can range from one digit up to five depending upon the detail of the criteria employed in the diagnosis. Clinical features and diagnostic criteria are provided for more than 200 subforms of headache-related disorders with the goal of having the coding system eventually synchronized with the World Health Organization s ICD-11. Of particular interest for oral medicine specialists are Category 11 within Part II and more specifically Category 13 within Part III. Category 11 focuses on secondary headache as a comorbidity of pain disorders arising from orofacial and neck structures while subcategories 11.6 and 11.7 includes, respectively, diagnostic criteria for headache attributed to disorder of the teeth or jaw, and headache attributed to TMDs. As for Category 13, it provides a list and a detailed description along with diagnostic criteria for coding the painful craniofacial neuropathies and related facial pain conditions. Upon viewing Table 3 one can better appraise similarities and differences between the ICHD-3 and the IASP for the classification scheme and denomination of craniofacial neuralgias. Advantages and limitations: The IHS classification is easy to use and depending on how specific one needs to rule-in a diagnosis it offers a flexible hierarchical coding system and diagnostic criteria for all the conditions in a standardized format. The diagnostic criteria are clearly presented and easy to follow. These are empirically derived and have good face and content validity, but their accuracy has yet to be tested in field studies. The ICHD-3 is mostly useful for patients with headache, facial neuralgia, or painful trigeminal neuropathy. All the other clinical phenotypes of OFP-related disorders are not described in this classification system, thus limiting its general use in clinical situations involving a spectrum of OFP patients (Zebenholzer et al. 2005; Benoliel et al. 2008, 2010). One can overcome this limitation by referring to other classification systems. As mentioned previously for the IASP axes, no due consideration is given to the biopsychosocial and behavioral factors in any part of the ICHD-3. American Academy of Orofacial Pain The American Academy of Orofacial Pain (AAOP) and its worldwide sister organizations regroup dentists and allied professional practitioners with interest in TMDs and face pain. In 1990, the AAOP published its first handbook and guidelines that focused solely on the diagnosis and management of TMDs. From the second to the present fifth edition (2013) however, the AAOP have broadened its guidelines for assessment, diagnosis, and management to include all clinical phenotypes of OFP-related disorders whether it is acute or chronic (De Leeuw and

7 Classification of Orofacial Pain 7 Table 3 ICHD-3 Category 13 listing for painful cranial neuropathies and other facial pains and IASP Group II listing for Neuralgia of the Head and Neck (Merskey and Bogduk 1994; Headache Classification Committee of the International Headache Society 2013) ICHD Trigeminal neuralgia Classical trigeminal neuralgia Classical trigeminal neuralgia, purely paroxysmal Classical trigeminal neuralgia with concomitant persistent facial pain Painful trigeminal neuropathy Painful trigeminal neuropathy attributed to acute Herpes zoster Postherpetic trigeminal neuropathy Painful posttraumatic trigeminal neuropathy Painful trigeminal neuropathy attributed to multiple sclerosis (MS) plaque Painful trigeminal neuropathy attributed to a spaceoccupying lesion Painful trigeminal neuropathy attributed to other disorders 13.2 Glossopharyngeal neuralgia 13.3 Nervus intermedius (facial nerve) neuralgia Classical nervus intermedius neuralgia Nervus intermedius neuropathy attributed to Herpes zoster 13.4 Occipital neuralgia 13.5 Optic neuritis 13.6 Headache attributed to ischemic ocular motor nerve palsy 13.7 Tolosa-Hunt syndrome 13.8 Paratrigeminal oculosympathetic (Raeder s) syndrome 13.9 Recurrent painful ophthalmoplegic neuropathy Burning mouth syndrome (BMS) Persistent idiopathic facial pain (PIFP) Central neuropathic pain Central neuropathic pain attributed to multiple sclerosis (MS) Central post-stroke pain (CPSP) IASP 1. Trigeminal neuralgia 2. Secondary trigeminal neuralgia from the central nervous system 3. Secondary trigeminal neuralgia from facial trauma 4. Acute herpes zoster 5. Postherpetic neuralgia 6. Geniculate neuralgia (Ramsey-Hunt Syndrome) 7. Neuralgia of the nervous intermedius 8. Glossopharyngeal neuralgia 9. Neuralgia of the Superior laryngeal nerve 10. Occipital neuralgia 11. Hypoglossal neuralgia 12. Glossopharyngeal pain from trauma 13. Hypoglossal pain from trauma 14. Tolosa-hunt Syndrome 15. SUNCT Syndrome 16. Reader s (paratrigeminal) Syndrome Klasser 2013). Except for TMDs, no detailed classification and listing are provided by the AAOP for other subtypes of OFP disorders. Nevertheless, how the AAOP handbook is organized enables one to capture the scope and breadth of OFP conditions while also providing an informal classification scheme mainly based on a topographical approach and various tissue, structures, or organ systems that can give rise to oral and craniofacial pain. The chapter headings listed in Table 4 presents the different categories of craniofacial pain phenotypes that exemplifies what is considered as the AAOP classification scheme. Of particular interest is the designation provided by the AAOP when referring to neuropathic pain and primary headache disorders. The endorsement of the ICHD-3 scheme and denominations developed by the IHS avoid confusion and lack of concordance. As for TMDs, the AAOP uses the expanded taxonomy developed jointly with the International RDC-TMD Consortium Network that is presented in Table 5 (Peck et al. 2014). The expanded taxonomy is however a compilation of all types of TMD and hence it includes painful and non-pain conditions. Advantages and limitations: Although the AAOP guidelines do not offer a comprehensive classification scheme and specific listing of OFP-related conditions but for TMDs, it nevertheless provides a taxonomic structure that covers the entire spectrum of OFP conditions (Peck et al. 2014). Choosing to refer to the ICHD-3 for

8 8 G.D. Klasser et al. Table 4 Classification structure of orofacial pain conditions from the 5th edition of the American Academy of Orofacial Pain guidelines (De Leeuw and Klasser 2013) Vascular and nonvascular intracranial cause of orofacial pain Headache associated with vascular intracranial disorders (IHS/ICHD-3 code 6.1 to 6.6) Headache associated with nonvascular intracranial disorders (IHS/ICHD-3 code 7.1 to 7.8) Primary headache disorders Migraine (IHS/ICHD-3 code 1.1 to 1.6) Tension-type headache (IHS/ICHD-3 code 2.1 to 2.4) Cluster headache and other trigeminal autonomic cephalalgias (IHS/ICHD-3 code 3.1 to 3.5) Neuropathic pain Episodic neuropathic pain (IHS/ICHD-3 code , 13.2, 13.3, 13.9) Continuous neuropathic pain (IHS/ICHD-3 code , 13.10, 13.11, ) Dysesthesia Intraoral pain disorders Odontogenic pain Non odontogenic pain Oral mucosal pain Temporomandibular disorders (see Table 5) Temporomandibular joint disorders Masticatory muscle disorders Extracranial causes of orofacial pain and headaches Pain stemming from tissues or organs in the head and neck (IHS/ICHD-3 code 11.1, 11.3 to 11.5) Pain stemming from systemic disease (IHS/ICHD-3 code ) Cervicogenic mechanisms of orofacial pain and headaches Common cervical spine disorders (IHS/ICHD-3 code 11.2, 11.8, 13.2, 13.4) IHS International Headache Society, ICHD-3 International Classification of Headache Disorders headaches and craniofacial neuralgia, the AAOP ensures better communication through already recognized denominations of entities thus reducing confusion and misunderstandings. Clear operationalized and validated diagnostic criteria are only available for the most common painrelated TMDs through the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) classification system embedded in the expanded TMD taxonomy. While there is an enormous task ahead regarding the validation of existing empirically derived diagnostic criteria for other OFP conditions, the fact that pain-related TMDs represent the most common type of nondental OFP makes the validated DC/TMD highly useful for patient triage and clinical decision making. As for the psychological and behavioral factors that may impact on the patient s pain experience and response to treatment, the AAOP fully recognizes the importance of implementing a dual-axis diagnostic framework but does not recommend any specific classification system for that matter. American Academy of Craniofacial Pain The American Academy of Craniofacial Pain (AACP) is another professional organization with interest in the assessment, diagnosis, and management of craniofacial pain disorders that published its own guidelines in 2009 (American Academy of Craniofacial Pain 2009). The AACP has not developed its own classification system but uses existing taxonomies. Hence, for neuralgias of the head and neck and for headache disorders, the AACP follows the classification by the IASP for the former, and the IHS classification schemes for the latter. As for TMDs it uses the classification proposed by Pertes and Gross for masticatory muscle and joint disorders (Pertes and Gross 1995). Craniofacial pain disorders stemming from other structures or anatomical parts are specifically addressed throughout the AACP handbook in dedicated chapters (Table 6). When comparing Tables 4 and 6, one can see some similarities on how the AACP and the AAOP categorize oral and craniofacial pain disorders, but discrepancies are unveiled upon closer inspection at the list of clinical entities included in each pain sub-category. Advantages and limitations: There is no real advantages for use of the AACP classification structures considering it refers to existing taxonomy whenever possible and for TMDs, the expanded taxonomy developed jointly by the RDC-TMD International Consortium integrates all musculoskeletal disorders and provides unambiguous operationalized diagnostic criteria with known validity for the most common disorders. For example, there are two different listings of masticatory

9 Classification of Orofacial Pain 9 Table 5 Expanded taxonomy for temporomandibular disorders (Peck et al. 2014) I. Temporomandibular joint disorders 1. Joint pain A. Arthralgia a B. Arthritis a 2. Joint disorders A. Disk disorders 1. Disk displacement with reduction 2. Disk displacement with reduction with intermittent locking 3. Disk displacement without reduction with limited opening 4. Disk displacement without reduction without limited opening B. Hypomobility disorders other than disk disorders 1. Adhesions/adherence 2. Ankylosis a. Fibrous b. Osseous C. Hypermobility disorders 1. Dislocations a. Subluxation b. Luxation 3. Joint diseases A. Degenerative joint disease 1. Osteoarthrosis 2. Osteoarthritis a B. Systemic arthritides a C. Condylysis/Idiopathic condylar resorption D. Osteochondritis dissecans E. Osteonecrosis F. Neoplasm G. Synovial chondromatosis 4. Fracture a 5. Congenital/developmental disorders A. Aplasia B. Hypoplasia C. Hyperplasia a Pain-related TMD II. Masticatory muscle disorders 1. Muscle pain A. Myalgia a 1. Local myalgia a 2. Myofascial pain a 3. Myofascial pain with referral a B. Tendonitis a C. Myositis a D. Spasm a 2. Contracture 3. Hypertrophy 4. Neoplasm 5. Movement disorders A. Orofacial dyskinesia B. Oromandibular dystonia 6. Masticatory muscle pain attributed to systemic/central pain disorders A. Fibromyalgia/widespread pain a III.Headache 1. Headache attributed to TMD a IV.Associated structures 1. Coronoid hyperplasia muscle conditions in the AACP guidelines, one under the heading of Extracapsular Temporomandibular Disorders and the other under Temporomandibular Disorders as classified by Pertes and Gross (1995; American Academy of Craniofacial Pain 2009). Moreover, diagnostic criteria are provided in various formats that go from a precise list of clinical features (muscle disorders) to a more narrative description of the condition (joint disorders). Current TMD Classification Systems RDC-TMD to DC-TMD and the Expanded TMD Taxonomy In 1992 Dworkin and LeResche published the Research Diagnostic Criteria for Temporomandibular Disorders (RDC-TMD), a dual-axis assessment protocol with operationalized diagnostic algorithms for the most common TMDs (Dworkin and LeResche 1992). The RDC-TMD is an empirically derived classification system

10 10 G.D. Klasser et al. Table 6 Classification structure of orofacial pain according to the American Academy of Craniofacial Pain guidelines (American Academy of Craniofacial Pain 2009) Extracapsular temporomandibular disorders Muscle disorders Ligament/tendon disorders Headache pain Primary (IHS/ICHD-3 Part one) Secondary (IHS/ICHD-3 Part two) Other headache (IHS/ICHD-3 Part three code 14) Neuralgias, nerve trunk and deafferentation pain Neuralgia of the head and face (IASP Group II) Viral neuralgia Miscellaneous facial pain Central cause of craniofacial pain Sympathetically maintained pain/complex regional pain syndromes Temporomandibular disorders (Adapted from Pertes and Gross 1995) Temporomandibular joint disorders Masticatory muscle disorders Congenital and developmental disorders Myofascial pain Additional structures that can cause craniofacial pain Eye, ear, hamulus process, hyoid bone, salivary glands, lymph nodes, occipital nerve, temporal, and carotid artery. Non odontogenic intraoral pain disorders Mucogingival pain Glossal pain IHS International Headache Society, ICHD-3 International Classification of Headache Disorders, IASP International Association for the Study of Pain based on the biopsychosocial model of pain that was primarily intended for research purposes. Axis I allows the rendering of a physical diagnosis for the most common pain and nonpain-related TMDs using a standardized and reliable examination protocol. On the other hand, Axis II tools enable one to identify the relevant psychosocial characteristics of the patients through the assessment of the psychological status and the grading of TMD pain-related disability. The growing appreciation for the RDC-TMD has made it a reference protocol for TMD research and that led to their translation into more than 20 languages ( With time, the RDC-TMD gained acceptance among clinicians who began to implement their use in a clinical setting (Manfredini et al. 2006). A number of authors started questioning the validity of the diagnostic criteria for an Axis I physical diagnosis and showed the need to improve the original RDC-TMD (Ohlmann et al. 2006; De Boever et al. 2008; Schmitter et al. 2008; Steenks and de Wijer 2009). This led to the funding of a carefully planned multisite Validation Project to assess the criterion validity of the RDC-TMD Axis I physical diagnosis for the most common TMDs and reviewed all Axis II screening tools for the evaluation of psychosocial and behavioral factors (Schiffman et al. 2010a). The results of this landmark study initiated the transition towards the new evidence-based diagnostic criteria for the most common pain and nonpain-related TMDs (DC-TMD) that were recently implemented for utilization in research and clinical settings (Schiffman et al. 2014; Schiffman and Ohrbach 2016). Table 7 presents the list of Axis I physical diagnoses that were part of the original RDC-TMD and compares that to the new DC-TMD along with the sensitivity and specificity establishing the level of accuracy for the new diagnostic criteria. While the DC-TMD for the most common TMDs were finalized, a joint effort by the RDC-TMD International Consortium Network and the AAOP led to the development of an expanded taxonomy (see Table 5) with the inclusion of empirically derived expert-based diagnostic criteria for the less common TMDs (Peck et al. 2014). As mentioned previously, the expanded taxonomy is inclusive for all subtypes of TMD whether it causes pain or not. It is important to know that within this framework, multiple diagnoses are also allowed except for conditions belonging to the same subgroup of disorders. For example, arthralgia and arthritis are mutually exclusive diagnoses within the joint pain category and so are the four muscle pain entities and the myalgia subtypes. Hence, that means for joint conditions where pain is not part of the diagnostic algorithm such as degenerative joint disorder and disk displacement with or without reduction, a diagnosis of arthralgia or arthritis can also accompany the primary diagnosis if joint pain is present.

11 Classification of Orofacial Pain 11 Table 7 Original Axis I RDC/TMD and validated Axis I DC/TMD with sensitivity (Sens.) and specificity (Spec.) values (Dworkin and LeResche 1992; Schiffman et al. 2014) RDC/TMD (1992) DC/TMD (2014) I. Muscle disorders A. Myofascial pain B. Myofascial pain with limitation II. Disk displacement disorders A. Disk displacement with reduction B. Disk displacement without reduction with limited opening C. Disk displacement without reduction without limited opening III. Arthralgia and other joint disorders A. Arthralgia B. Osteoarthritis C. Osteoarthrosis I. Pain-related temporomandibular disorders A. Myalgia (Sens. 0.90/Spec. 0.99) 1. Local myalgia 2. Myofascial pain 3. Myofascial pain with referral (Sens. 0.86/Spec. 0.98) B. Arthralgia (Sens. 0.89/Spec. 0.98) C. Headache attributed to TMD (Sens. 0.89/Spec. 0.87) II.Intra-articular temporomandibular disorders A. Disk displacement with reduction (Sens. 0.34/Spec. 0.92) B. Disk displacement with reduction with intermittent locking (Sens Spec. 0.98) C. Disk displacement without reduction with limited opening (Sens. 0.80/Spec. 0.97) D. Disk displacement without reduction without limited opening (Sens. 0.54/Spec. 0.79) E. Degenerative joint disease (Sens. 0.55/Spec. 0.61) F. Subluxation (Sens. 0.98/Spec. 1.00) What mostly distinguishes the DC-TMD from other classification systems is Axis II aimed to assess the psychosocial and behavioral factors that impact on the patients pain and can influence treatment outcome and chronicity (Dworkin et al. 2002). One of the Axis II tools is the Graded Chronic Pain Scale (available for download at: a simple seven items questionnaire that measures painrelated disability and intensity (Von Korff et al. 1992). This is a simple and easy to use questionnaire that can assist the clinician in identifying patients with high pain-related disability profile and decreased functioning which then usually requires additional expertise for the implementation of more comprehensive management strategies (Kotiranta et al. 2015). Advantages and limitations: The DC-TMD is the only system that uses standardized and reliable self-report questionnaires, clinical examination procedures, scoring systems, and decision trees while also providing estimates regarding the diagnostic accuracy of the history and examination criteria for the most common pain-related and intra-articular TMDs. No other system integrates biophysical diagnosis to a disability index that measures the impact the pain has on the patient s behavior. In addition, the assessment tools for implementing this dual-axis framework and a short TMD pain screener questionnaire with very good sensitivity and specificity are made available for download on the International RDC-TMD Consortium Network website (available for download at: org/) (Gonzalez et al. 2011). Except for two subtypes of myalgia (local myalgia and myofascial pain) what can be expected in terms of true- and false-positive diagnosis when using the DC-TMD assessment protocol for pain-related TMD is somewhat predictable. Sensitivity and specificity that reach 80% and 95%, respectively, make the DC-TMD scheme highly recommended to render a definitive clinical diagnosis for myalgia, myofascial pain with referral, arthralgia, disk displacement without reduction with limited opening, and subluxation. On the other hand, because the DC-TMD relies solely on clinical examination procedures, the utility is limited regarding the other disk displacement disorders and degenerative joint disease that are best assessed with Cone Beam CT and MRI imaging of the joint. With a diagnostic accuracy that is below 70% for true positive diagnosis (sensitivity), the respective DC-TMD for the above mentioned disorders can be used only to render a preliminary clinical diagnosis. Finally, it is premature to recommend using the operationalized diagnostic criteria that were

12 12 G.D. Klasser et al. developed for the less common disorders listed in the expanded TMD taxonomy other than for a preliminary diagnosis. This is because none have been tested yet against an acceptable reference standard. Nevertheless, the expanded TMD taxonomy still represents the most validated reference classification system for TMDs. Proposed Classification Systems Over the years, several classification systems have been proposed as alternative options or integrations to currently adopted schemes. Some of them focused on chronic idiopathic OFP (Woda et al. 2005), some other addressed specifically the field of TMDs (Stegenga 2010; Machado et al. 2012), and others more embedded an all-inclusive proposal for OFP (Okeson 2014). They will be reviewed briefly below. Classification of Chronic Idiopathic Orofacial Pain: Woda et al. (2005) Based on purported shortcomings of the literature on the taxonomy of the different forms of chronic idiopathic OFP, a prospective multicenter study was performed to provide a better framework for introducing entities such as stomatodynia, atypical odontalgia, atypical facial pain, and facial arthromyalgia within the broader context of OFP (Woda et al. 2005). The authors pointed out that those forms of idiopathic OFP are sometimes grouped together and sometimes considered separate conditions, and so, developed a new taxonomy based on the results of cluster analysis. The underlying premise of this proposal was rather intriguing, since the authors hypothesized that the main subgroups of OFP syndromes (i.e., atypical facial pain, atypical odontalgia, stomatodynia, temporomandibular disorders), which display some common clinical features, may correspond to a single disease expressed in different tissues: teeth, bone, oral mucosa, muscle, and joint. Based on that, they assessed the possibility of proposing a classification that takes into account the presence of similar signs/symptoms and thus reflects similar pathophysiological mechanisms and treatment approaches, rather than topography, organs, or tissues. In short, the classification system results from a 111-item selfreported questionnaire including questions on pain evaluation, impact of pain on health-related quality of life, and psychological self-evaluation. Furthermore, an experienced examiner completed an 8-item record that exited in a tentative diagnosis. A multivariate analysis trying to identify clusters of self-reported and clinically recorded signs and symptoms led to the identification of very similar and common mechanisms between conditions affecting the different stomatognathic structures. Three subgroups of idiopathic disorders were thus identified: stomatodynia, arthromyalgia, and atypical facial pain, whose differences are essentially based on topographic criteria. A notable feature of this proposal is that the term arthromyalgia is introduced to discriminate those idiopathic conditions, viz., joint and/or muscle pain of uncertain or unknown origin, from TMD symptoms of certain origin, such as conditions linked to general diseases. Classification of TMJ Disorders: Stegenga (2010) An interesting proposal for the classification of TMJ disorders was proposed by Stegenga (2010), who suggested that instead of positional classification relating the presence of joint pathology to the position of the disk, a classification system based on the actual intra-articular structural changes could be more suitable for clinical purposes. The point of this classification system was that, even if many clinical signs, and most notably joint sounds, are explainable with the presence of disk displacement, the increasing amount of knowledge on the actual pathologic changes occurring within the joint should have led to more structurally oriented classification systems. Based on that, two major categories of structural disorders have been identified by the author, viz., the arthritic disorders (i.e., inflammatory

13 Classification of Orofacial Pain 13 disorders affecting the joint, which are mainly characterized by pain and function impairment) and the growth disorders (which are mainly characterized by facial asymmetry). In short, the author proposed that mechanical derangements are only one of the possible consequences of pathological changes occurring in temporomandibular joints with a maladaptive load response. Thus, the author suggested classifying TMJ disorders into three main categories: arthritic disorders, growth disorders, and nonarthritic disorders. The latter are noninflammatory in nature, contrary to the arthritic disorders, which may have a mechanical component (i.e., disk displacement), but are related to a joint disease due to tissue changes at the molecular level and present with pain as the main symptom. This classification has merits, and years after its proposal some evidence is developing in support of this concept, but it should be considered a hypothesis-driven, opinion-based, taxonomy that was not supported with any specific investigation. Classification Profile of TMD Patients: Machada et al. (2012) Also in the TMD field, Machado and colleagues (Machado et al. 2012) performed a large-sample investigation attempting to profile the clinical presentation of diagnostic characteristics of TMD patients. The authors aimed to simultaneously classify symptomatic patients diagnosed with a variety of TMD subtypes into homogeneous groups based on their clinical presentation and occurrence of comorbidities. The study design involved a retrospective assessment of more than 300 clinical records based on the AAOP guidelines published in 2008 (De Leeuw 2008), and the resulting diagnoses were clustered into groups based on symptoms occurrence. Based on this analysis, four main symptomatic profiles were identified: acute muscle pain (35.0%), nonpainful articular impairment (33.9%), acute articular pain (21.0%), and chronic facial pain (10.1%). Those groups are homogeneous as for their clinical presentation, and their names were suggested by the authors as being intuitively linked to the time of onset, the location, the presence of pain, and extent of the symptoms. According to the authors, this proposal may shed light on the most suitable strategy that should be adopted to manage TMD patients seeking treatment. Classification of Orofacial Pains: Okeson (2014) A broadly diffused, opinion-based, comprehensive classification scheme for OFP came from the work(s) of Okeson (2014). The concept behind the proposal is that a reliable pain classification needs to be based on symptomatology. Based on that, pain conditions may be grouped into somatic and neurogenous. Somatic pains occur in response to the stimulation of normal neural receptors, while neurogenous pains originate due to dysfunctional neurologic structures. According to the proposed classification, somatic pain may be superficial or deep. The former may originate from cutaneous or mucogingival sources, which share the following clinical features: (a) the pain has a bright, stimulating quality; (b) subjective localization of the pain is excellent and anatomically accurate; (c) the site of pain identifies the correct location of its source; (d) response to provocation at the site of pain is faithful in incidence, intensity, and location; (e) the application of a topical anesthetic at the site temporarily arrests the pain. Alternatively, deep somatic pain may be visceral or musculoskeletal in origin, is less accurately localizable by the patient than superficial pain, and may not be proportionally related to the noxious stimulus. As a general remark, deep somatic pains share the following features: (a) the pain has a dull, depressing quality; (b) subjective localization of the pain is variable and somewhat diffuse; (c) the site of pain may or may not identify the correct location of its true source; (d) response to provocation at the source of pain is fairly faithful in incidence and intensity; and (e) secondary central excitatory effects frequently accompany the deep pain.

14 14 G.D. Klasser et al. Sometimes, the pain felt in somatic structures may be actually originating in neurogenous tissues. Such conditions have been grouped together by the author as neuropathic pains. Those pains usually feature a burning sensation and can present as either episodic or continuous pain. In his proposal, the author posited that at least two groups of episodic neuropathic pains can be identified (i.e., neurovascular pain such as headaches; paroxysmal neuralgic pain such as neuralgias) as well as three groups of continuous neuropathic pains (i.e., metabolic polyneuropathies; peripheral mediated pain such as deafferentation pain; central mediated pain such as atypical odontalgia, burning mouth syndrome, and complex regional pain syndromes). This classification also encompasses a group of so-called Axis II psychological conditions, comprising mood, anxiety, somatoform, and other disorders of the psychosocial spectrum that may complicate the history taking and clinical examination and should most certainly be taken into account for a definitive diagnosis especially with the chronification of pain. Psychosocial Subtyping of TMD Patients: Suvinen et al. (2005) The importance of Axis II profiling of pain patients has been highlighted in several seminal papers on TMD, which have been summarized in the classification proposal of Suvinen and colleagues (Suvinen et al. 2005). They emphasized and highlighted that despite variability in terminology provided by authors as well as methodologies employed as to how the patients are categorized, there appears to be at least three main groups or subtypes of TMD patients based on the importance of physical versus psychosocial impairment: (i) a biologically/somatically defined TMD patient group; (ii) an intermediate group, with patients who report fluctuating or recurrent symptoms of TMD, but are generally viewed as adaptive copers; and (iii) a complex/psychosocially dysfunctional TMD patient group. This identification of patients according to a tri-axial schematic may allow more keys as to what is the appropriate method of treatment for each patient group, but it should be noted that the method is not directly applicable in a clinical setting, since it involves the use of multiple psychometric evaluations and needs further validation to be more globally accepted. Interestingly, according to the therapeutic model associated with this classification proposal, it is suggested that the assessment and subtyping of patients can indicate the most appropriate form of treatment. In short, the simple TMD subtype appears to be more biomedically defined and therefore is most likely to benefit from relatively simple forms of conservative management, such as counseling, physical therapies, oral appliances, and medications for the acute phase. The intermediate TMD subtype appears biobehaviorally functional and is likely to benefit from combined biomedical and biobehavioral approaches of management, based on the appropriate assessment of possible contributing, aggravating, and maintaining factors. The complex TMD subtype appears similar to the minority of patients who may report psychological distress and psychosocial dysfunction that is poorly correlated with biomedical and physical findings. This group of patients also appears to be unable to cope and present with higher rates for depression, somatization, maladaptive coping strategies, sick-leave, and health care utilization. These patients may be most appropriately managed in multidisciplinary pain management clinics, with appropriate skills to assess also indicators for hypochondriasis, somatoform disorders, and severe life stress, as well as general vulnerability to possible idiopathic pain disorders in general. Based on estimates in epidemiological and clinical studies, the distribution of these subtypes within the community differs from those in the tertiary referral clinics, with a preponderance in the simple/intermediate groups and a small minority in the complex group.