CRITICAL COMMENTARY 1 A UNIFIED CONCEPT OF IDIOPATHIC OROFACIAL PAIN: CLINICAL FEATURES

James R. Fricton, DDS, MS Professor, Diagnostic and Surgical Sciences University of Minnesota School of Dentistfy Minneapolis. Minnesota 55455 Fax:612-626-0138 E.mail: [email protected]

iagnostic classifications of pain disorders those in the AAOP classification, there are many can be particnlarly useful if defined care- similarities in terminology and definitions. D fully to include a set of homogeneous dis- However, the ptoblems that exist with the AAOP orders wirh similar etiology and characteristics. classification system have not been solved by this This allows researchers to investigate further the new proposal. For example, the proposal still underlying mechanisms associated with the disor- leaves us with confusion regarding the etiologic der and can lead to treatment strategies that are process, the peripheral or central mechanisms based on these mechanisms. In theory, treatment involved in each of these disorders, and the epi- strategies can be designed to target these mecha- demiology. !n addition, since there is no new scien- nisms with a higher degree of predictability and tific data presenred that studies the reliability or prognosis. Risk factors and comorbidities can be validity of the proposed classification, there is no identified to help understand prevention and pro- additional knowledge to provide a basis for it. gression. It also enhances communication among It is no longer acceptable to define a pain disor- clinicians, parients, and researchers within the sci- der by clinical criteria only, without consideration entific hterature. A working classification of orofa- of the underlying mechanisms and etiology associ- cial pain disorders is critical to simplify the process ated with it. Only by understanding this process of obraining a physical diagnosis and, thus, the can we make sufficient progress in developing pretnise for Woda and Pionchon's focus article' on treatment strategies that have the best potential for idiopathic pain is appreciated. success. Although this can be a complex process, there is some precedent. A group of scientists and pain clinicians gathered in 1997 to help develop Comparison with Existing Classifications and propose a mechanism-based classification for pain disorders'* (Table 1). In this classification, These authors suggest that at>'pical orofacial pain they proposed specific levels of pain disorders that disorders that have primary characteristics involving are based on the peripheral and cenrral mecha- imdiagnosed pain in the teeth or face do not fit well nisms and their modulating effects. This classifica- into currenr diagnostic classifications, are poorly tion helps not only to clarify the various levels of understood, and thus warrant better definition. mechanisms associated with specific disorders but They suggest that these disorders may be categorized it can also directly translare into rationales for more accurately into 4 diagnostic groups: (1) atypi- multi-modality treatment approaches with chronic cal facial pain; (2) atypical odontalgia; (3) stomato- pain. A new classification proposed for orofacial dynia; and (4) idiopathic facial arthromyalgia. pain would be improved by such an etiology-based In proposing any new classification, it is impor- approach to classification. tant to build on the knowledge used to define cur- rent classification systems. The most complete diagnostic classification of orofacial pain disorders Is a Wastebasket has been the American Academy of Orofacial Pain (AAOP) Guidelines.- These guidelines have inte- Term for Difficult-to-Diagnose Oral, grated the International Headache Society classifi- Perioral, and Facial Pain Disorders? cation with the AAOP classification for temporo- mandibular disorders.^ In comparing the The AAOP guidelines suggest that the diagnosis of categories proposed by Woda and Pionchon with atypical facial or oral pain is not specific for any

Journal of Orofacial Pam 185 Fricton

Table 1 Categories of Pain and Possible Mechanisms''' Category Possible Mechanism Transient pain' NQOiceptor specialization Tissue injury pain Pnmary afferent Peripheral sensit i nation Recruitment of silent naciceptors Alteration of phenotype Hyperin ne relation Central neivous system- Central sensitization with recruitment, mediated summation, and amplification Nervous system injury pain Primary afferent Acquisition of spontaneous and stimulus- evoked actiuity by nociceptor axons and somata at loci other tban peripheral terminals Phenotype change Central nervous system- Central sensitization riediated Deafferentation of second.order neurons Disinhibition Structural reorganization 'According lo Woolf el al.-* 'Resppnse to a noiious stimulus that does not produce long-te nek

known etiology or disorder and is, therefore, an patients was 69% female and 31% male, with a undesirable term for an orofacial pain disorder.- mean age of 44.5 years. The persistent nature of The guidelines suggest that prior to tbe use of a these problems was evident in the mean of 2.1 diagnosis of "atypical facial pain," all other local years since onset and the mean of 2.8 clinicians or systemic causes, whetber dental, oral, facial, seen prior to referral to the pain clinic. sinus, tieuropatbic, mu.sculoskeletal, or intracra- The distribution of tbese disorders was: myofas- nial, mtist be excluded. Wben doing so, it is possi- cial referred pain (54%), periodontal ligament sen- ble tbat most, or perhaps all, of tbe patients wbo sitivity pain (31%], referred pain from originally appear to have atypical facial pain or (23%], tieuropatbic pain (9%), burning atypical odontalgia do not retain the diagnosis tongue/moutb (6%), tootb fracture (3%), occlusal after a definitive diagnosis is made. It is possible awareness dysfunction (3%), candidiasis (3%), tbat tbe diagnosis of atypical facial pam or odon- sinus pathology (3%), atid (3%]. Tbe talgia is simply a diagnosis that is yet to be deter- most difficult of the disorders to diagnose and, mined. If so, the need for a wastebasket term for thus, often overlooked in tbe clinical diagnostic undiagnosed facial pain is questtonable, and a process by referring providers, include: clearer diagnosttc term could be used: "undiag- nosed orofacial pain." " Myofascial Referred Pain. Myofascial pain is To evaluate tbis possibility, a retrospective anal- characterized by a regional, dull, aching muscle ysis of 493 consecutive charts for patients who pain and the presence of localized tender sites presented to an orofactal pain clinic associated ¡trigger points] in muscle, tendons, or fascia.^'^ with the University of Minnesota was conducted. When palpated, these trigger points may pro- Of these patients, 35 (7.1%) presented with a chief duce a characteristic pattern of regional referred complaint of persistent undiagnosed perioral, oral, pain and/or autonomie symptoms on provoca- or facial pain and a potential diagnosis of atypical tion. They often refer pain to areas of the face facial pain or odontalgia. Tbe distribution of diag- and teeth distant from the muscles that are gen- noses that were provided by the using the erating the pain. In the cases described, the most AAOP diagnostic categories is listed in Table 2. In common muscles referring pain to the face and all but 1 of these cases (97%), there was a specific teeth were the masseter, the temporalis, and the physical disorder or disorders that were deter- medial pterygoid. mined to cause the persistent pain, and only ] case • Periodontal Ligament Sensitivity Pain. was unable to be diagnosed. The gender of these Petiodontal pain is characteristic of deep

186 Volume 13, Number3, 1999 Fricton somatic pain of the musculoskeletal type and is Table 2 Diagnoses of 35 Patients Who Presented caused hy repetitive strain to the periodontal lig- with Persistent Undiagnosed Oral, Perioral, and aments through clenching, gross occlusal prema- Facial Pain* turities, or repetitive trauma to the teeth,'-^"'^ Periodontal ligament pain is generally a dull, Actual diagnosis No, of patiencs % of pa aching pain in and around che teeth and can Myofasciei referred pain 19 54.2 afiect multiple teeth. Inflammatory fluid aecu- to teeth and face Periodonlai ligament 11 31 4 tnulation may cause displacement of the tooth in sensitivity pain its socket, with a resulting acute Referred pain from dentai 8 22.S and pain. The most common sign is tenderness of the teeth to percussion in the absence of pul- Neuropatbic pain 3 8.6 pitis, periapical abscess, or . Buming moutii from 1 2.9 Neuropathic facial or Dental Pain. Advance- Sinus palhoiogy 1 2.9 ments in rhe understanding of neuropathic pain Burning tongue pain Erofn 1 2.9 conditions have helped explain some pain disor- tongue habit ders chat have been previously categorized as Pericoronitis causing 1 atypical facia! pain.'-"'^ This category of pain is faciai pain a continuous, daily pain, often described as a Incomplete tooth fracture 2.9 Unknown 1 2,9 burning or tingling, that is limited to a specific 'As determined hy the American Academy of Orofacial Pain Guideline nerve distribution. Hisrorically, rhe pain usually Total more than 35 because some patients had multiple diagnoses, p begins following surgery or injury of the face, Eicula'ly myofascial pain and penodontai ligament sensitivity. teeth, or but continues despite healing and che absence of a demonstrable etiology. Anesthetic nerve blocks can be used diagnosti- cally CO decrease the pain for the duration of rhe anesthetic. tetized by a constant burning sensation and is • Tooth Fractures. Complete or incomplete tooth frequently associated with a prior history of tis- fractures can cause persistent tooth pain that is sue damage.^^'^^ The main clinieal features difficult to diagnose.''"'^ Pain can result when include pain described as hurning and continu- rhe pulp is exposed as a result of fractures to the ous that is exacerbared hy movement, cutaneous enamel and that become displaced when stimulation, or srress; onset is usually weeks mechanical strain is placed on the tooth. after injury. Confirmation of SMP of the tooth Diagnosis is difficult, patticularly if an incom- or facial area is achieved by srellate ganglion plete fracture is present, but it can be made by blockade of the sympathetic neural input to the visual inspection, exploration of the tooth for painful region. loose fragments, rooth mobility tests, tooth dis- . Patients with idio- colorarion, and tooth provocation tests that pathic hurning mouth syndrome typically char- cause pain when the fractured segtnent is acterize their symproms as a burning sensation, moved. The pulps of these teeth may or may not as if the mouth or tongue were scalded or on respond to an electric pulp cesr or to chermal fire; this can accompany other oral complaints, testing. including xerostomia and dysgeusia.^''"^^ The ' Referred Pain from . Pulpitis oral tissues often appear normal. There are and periodontal pathology can present diagnos- many factors that can cause burning mouth syn- tic dilemmas if they refer pain to areas that are drome, including candidiasis, painful geographic distant from the mvolved tooth. "•-'''^' Although and/or , as well as parafunctional uncommon, patients may present with tooth- habits, dysfunctional disorders of the muscu- ache in a tooth that responds normally to all loskeletal system, allergies, xerostomia, and available tests. Further pulp testing or radio- injury following dental treatment. Systemic dis- graphs reveal that an adjacent tooth or other ease and medications have also been shown to distant tooth or periodontal structure is cause burning mouth, either directly or indi- inflamed. Subsequent treatment to the inflamed rectly, from the resultant xerostomia that may tooth resolves the referred pain. be present. Thus, it is nor as difficult to diagnose ' Sympathetically Maintained Pain. Sympa- a condition as burning mouth as it is to deter- thetically maintained pain (SMP, also termed mine che underlying etiology that will suggest a chronic regional pain syndrome) is often charac- treatment.

Journal of Orofaciai Pain 187 Fricton

The Need for Research in Classification tree is "pruned" (made simpler by deleting later of Pain Disorders splits) by cross-validation or other methods and evaluated for its ability to classify correctly. The AAOP classification of atypical orofacial pain The discriminant and classification analysis can disorders i.s particularly weak because it is not sup- result in the hypothesized diagnostic criteria being ported by specific basic or clinical science data. In supported or changed by modification through this regard, the proposed classification also pro- inclusion of new criteria and/or rejection of exist- ing ones. Regardless of the outcome, a study such vides no data to support the nature of the division. as this will be a major step toward development of The study described here suggests tbat most of a valid diagnostic criteria for any proposed idio- these cases meet diagnostic criteria for many other pathic orofacial pain disorders. disorders and that atypical facial pain, atypical odontalgia, stomatodynia, and atypical facial arthromyalgia may not be entities by themselves. However, if disorders called "atypical orofaciat Summary pain" do exist, further research is critical to estab- hsh clear diagnostic criteria for them, with docu- The rask of developing a classification system for mented reliability and validity. atypical facial pain is questionable, given that most To do this, studies of proposed criteria need to cases meet criteria for other orofacial pain disor- determine their convergence or divergence with ders that are difficult to diagnose. However, if dis- normal subjects and criteria for existing disorders. orders called "atypical orofacial pain" do exist, it Data of the characteristics of specific orofacial is critical to establish diagnostic criteria for these pain disorders should be collected with an exami- disorders, based on an underlying etiology with nation of consecutive patients who present witb documented reliability and vahdity, and include at undiagnosed facial or tooth pain by at least 2 inde- least: (II clinical data supporting hypothesized cri- pendent, blinded clinicians. Two methods, discrim- teria related to atypical facial pain, as defined in inant analysis and classification trees, can then be the existing AAOP classification; (2) consistency used to determine which set of independent vari- with basic science mechanisms of peripheral and ables discriminates best between tbe diagnostic central sensitization; and (3) data from a study subgroups of idiopathic orofacial pain disorders. A that includes at least discriminant analysis and/or linear discriminant analysis can be used to con- classification trees to determine which criteria dis- struct 2 or 3 linear combinations of the indepen- criminate best between the diagnostic subgroups. dent variables. Tbese combinations can be used to Adherence to these principles will provide the best define simple rules for classifying subjects.^^ A potential of adding to our existing classification a small number of independent variables can be set of criteria for atypical facial pain and atypical selected from a larger group by stepwise multiple odontalgia that will be accepted over the long term regression, in which an independent variable is and improve treatment of these disorders. included if, in conjunction with previously included variables, it contributes significantly to identifying a specific type of idiopathic orofacial References pain disorder. The discriminating power of rhe selected variables (ie, ability to classify correctly) is 1. Woda A, Pioncbon P. Focus article: A unified concept of idiopathic orofacial pain: Oinical fearures. J Orofac Pain measured by cross-validation. 1999; 13:172-184. A classification tree for orofacial pain diagnoses 2. Okeson JP (ed). Orofacial Pain: Guidelines for can also be constructed recursively. For each possi- Assessment, Diagnosis, and Management, Chicago: ble independent variable, a threshold is chosen Quintessence, 1996. such that when the population is split at the 3. Oleson J. Classification and diagnostic criteria for headache disorders, cranial neuralgias, and facial pain. threshold into 2 subpopulations, each of them is as Cephalalgia 198S;S(suppl 7):l-64. homogeneous as possible. The selected candidate 4. Woolf CJ, Bennet GJ, Doherry M, Dubner R, Kidd B, variable is the one that produces the 2 most homo- Koltienberg M, er al. Towards a mechanism-based classi- geneous subpopulations from the resulting opera- ficarion of pain? Pain 1998;77:227-229. tionally defined subpopulations. A similar method 5. Travell J. Identification of myofascial trigger point syn- involves further splitting the group into 2 sub- dromes: A case of atypical facial neuralgia. Arch Phys Med Rehahil 198I;62:1OO-1O6. groups. Dichotomous splitting continues recur- sively until the groups reach a minimum size or become perfectly homogeneous, at which point the

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Fricton J, Kroening R, Haley D, Siegert R. Myofascial 18. Andreasen JO. Treatment of fractured and avulsed teeth. pain syndrome of the head and neck: A review of clinical ASDCJ Dent Child I971;38:29-31. characteristics of 164 patients. Oral Surg Oral Med Oral 19. Wright EF, Gullickson DC. Identifying acure pulpalgia as Pathol 1985;60:615-623. a factor in TMD pain, J Am Dent Assuc 1996;i27: Travell J, Simons DG. Myofascial Pain and Dysfunction: 773-780. The Trigger Point Manual. Baltimore: Williams & 20. Falace DA, Muse TL. Clinical characteristics and patterns Wilkins, 1998. of referred odontogenic pain [abstract|. ] Dent Res Okeson JP. Etiology and treatment of occlusal pathosis 1993;71(special ibsue):l,187. and associated facial pain. J Prosther Dent 1981;45: 21. Zadik D, Chosack A, Eidelman E. The prognosis of trau- 199-204. matized permanent anterior teeth with fracture of the Okeson JP (ed). Bell's Orotacial Pains, ed 5. Chicago: enamel and dentin. Oral Surg Oral Med Oral Parhol Quintessence, 1995:239-249, 1979;47:I73-175. Ingle JI, Jaeger B, Fricton JR, Glick DH. Differential diag- 22. Morton MJ, Pitel ML. Reflex sympathetic dystrophy syn- nosis and treatment of oral and perioral pain. In: Ingle Jl, drome complicating the management of TMJ symptoms. Tainror JF (eds), , ed 3. Philadelphia: Lea and A case report. Cranio 1989;7:239-242. Febiger, 1985:526-532. 23.Janig W, Stanton-Hicks M (eds). Reflex Sympathetic Falace DA, Gailleteau JG. The diagnosis of dental and Dysrrophy; A Reappraisal. Seattle: IASP Press, orofacial pain. In: Falace DA (ed). Emergency Denral 1995:249-257. Care: Diagnosis and Management of Urgent Dental 24, Tourne LP, Fricton JR. Burning mouth syndrome. Critical Problems. Baltimore: Williams & Wilkins, 1995:1-24. review and proposed clinical management. Oral Surg Oral Graff-Radford SB, Solberg WK. Atypical odontalgia. GDA Med Oral Parhol 1992;74:158-167. J 1986; 14:27-32. 25. Grushka M, Sessle BJ. Burning mouth syndrome. Dent Fromm GH, Terrence CF, Marooti JC. Trigeminal neural- Clin North Am 1991;35:171-184. gia. Current concepts regarding etiology and pachogenesis. 2É. Bergdahl J, Anneroth G. Burning mouth syndrome: Aich Neurol 1984;4M204-1207. Literature review and model for research and manage- , Frgmm GH, Graff-Radford SB. Terrence CF, Sweet WH. ment. J Oral Parhol Med 1993;22:433^38. Pre-mgeminal neuralgia. Neurology 1990;40:1493-1495. 27. Bergdahl BJ, Anneroth G, Anneroth I. Clinical study of .Fromm GH, Sessle BJ (eds), Trigeminal Neuralgia: parienrs with burning mouth. Scand ] Dent Res Current Concepts Regarding Parhogenesis and Treatment. 1994;102(5):299-305. Boston: Butterworth-Heinemann, 1991. 28. Morrison DF. Multivariare Statistical Methods. New . Graff-Radford SB, Solberg WK. Atypical odontalgia. J York: McGraw-Hill, 1976. Craniomandib Disord Facial Oral Pain 1992;6:260-265. 29. Breiman L. Classification and Regression Trees (CART). . Ritchey B, Mendenhall R, Orban B. Pulpitis resulting from Belmont, CA: Wadsworth, 1984. incomplete tooth fracture. Oral Surg Oral Med Oral Pathol 1957;10:665.

CRITICAL COMMENTARY Zr A UNIFIED CONCEPT OE IDIOPATHIC OROEACIAL PAIN: CLINICAL FEATURES

Jeffrey P. Okeson, DMD Professor and Director OrofscisI Pain Center D-530 College of University of Kentucky Lexington, Kentucky 40536-0297 Fax:606-257-1847 E-mail: [email protected]

rs Woda and Pionchon have proposed the cians can appreciate their insights. From my adoption of a unified classification for perspective, most chnicians who treat orofacial D "idiopathic orofaciai pain disorders."' I pain disorders recognize that there are certain bdieve their motivation comes from their extensive patients who present with chnical symptoms that experience in the diagnosis and management of do not easily fit into the known and generally well- orofacial pain, for only the most experienced cHni- accepted classifications of orofacial pain disorders.

Journal of Orofaciai Pain 189