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 Atypical Facial Pain 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 tooth originally appear to have atypical facial pain or pathology (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 pericoronitis (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 dentists 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 malocclusion Referred pain from dentai 8 22.S and pain. The most common sign is tenderness pulpitis of the teeth to percussion in the absence of pul- Neuropatbic pain 3 8.6 pitis, periapical abscess, or periodontal abscess. Buming moutii from 1 2.9 oral candidiasis 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 gums but continues despite healing and che absence