1.1 Introduction and Definitions

Although there are many more than 30 orofacial pain conditions, this chapter focuses on the ones most commonly seen in clinical practice. The distinction between a disease, a disorder, and a dysfunction is somewhat arbitrary: The terms “disorder” and “dysfunction” are used more or less interchangeably to mean an ailment or impaired functioning of a bodily system The term “disease” implies a pathological condition of a part, organ, or system of an organism, resulting from various causes, such as infection, genetic defect, or environmental stress, and characterized by an identifiable group of signs or symptoms.¹ Regardless of how they are classified, these 30 conditions can be logically clustered into 7 subgroups. A clinician who can learn about these subgroups and distinguish between these 30 conditions will be a long way toward having the expertise required to properly manage patients with chronic orofacial pain. Toward this goal, the chapter begins with several tables that summarize information about the characteristics, appropriate diagnostic tests, age predilection, and known prevalence of these 30 conditions. These tables are accompanied by discussion of the process necessary to render a differential diagnosis for a patient with chronic orofacial pain complaints. Table 1.1 briefly describes the clinical characteristics of the 30 conditions considered in this chapter. Treatment of these 30 conditions is discussed, along with associated conditions, in various other chapters in this book and therefore is not covered here.

Table 1.1 The 30 most common orofacial-pain-related diseases and their distinguishing clinical features

AIDS, acquired immunodeficiency syndrome; BMMP, benign mucous membrane pemphigoid; CDH, chronic daily headache; CNS, central nervous system; CT, computed tomography; CTD, connective tissue disease; ddC, dideoxycytidine; ddI, dideoxyinosine; DDNR, disk displacement with no reduction; DDWR, disk displacement with reduction; DxTest, diagnostic test; ESR, erythrocyte sedimentation rate; HIV, human immunodeficiency virus; LP, lichen planus; MRI, magnetic resonance imaging; NSAIDs, nonsteroidal anti-inflammatory drugs; OA, osteoarthritis; SSRIs, selective serotonin reuptake inhibitors; TMJ, temporomandibular joint.

1.1.A Nociceptive Versus Neuropathic Pain

When pain persists beyond the time expected for healing to occur, two explanations exist. First, long-standing chronic pain sensations may still be occurring via local disease inducing pain mediators (e.g., inflammatory cytokines). Second, long-standing pain might be due to a “neuropathic conversion” due to sensitization of the peripheral and central nerves. The following five-step pathophysiologic process can be used to explain how this conversion occurs: (1) local cellular and humoral inflammation develops where tissue damage or ischemic injury occurs; (2) this inflammation means there is an accumulation of pain-inducing endogenous chemicals within the pain site; (3) altered peripheral neurogenic tissues develop because of these chemicals; (4) these altered nerves have lowered thresholds and even spontaneous activation; and (5) central sensitization and plasticity of the pain pathways from trigeminal nucleus or spinal cord to the cortex develop. Additional discussion of specific neuronal changes that occur in the nervous system with neuropathic pain is provided in Chapter 6, which focuses on neurogenic pain and anticonvulsant medications. This dichotomous etiology indicates that, in addition to making a diagnosis, you must also understand whether the pain is a typical nociceptive pain or an atypical neuropathic pain, because they have different prognoses and are treated quite differently.

1.1.B Differential Diagnosis and Etiology of Chronic Orofacial Pain

When a patient attends a physician’s or dentist’s office with a complaint of orofacial pain, they hope fervently that they will be given a diagnosis and an effective plan of treatment. Most physicians and dentists will perform an examination, take a careful medical history, and order appropriate tests. Based on this information, a diagnosis is usually rendered. For example, if a patient has pain on function, has limited mouth opening, and notices a crunching sound coming from one of the jaw joints, a diagnosis of localized osteoarthritis is certainly probable. If the disease has progressed far enough, a radiograph of the temporomandibular joint (TMJ) will confirm and document the magnitude of the osseous changes. Unfortunately, simply reformulating the patient’s complaint (painful, noisy joint) into medical nomenclature (osteoarthritis) is not sufficient. An expert clinician must strive to both find an etiology for the disease and understand the pathophysiologic basis for the pain itself, before this diagnosis is complete (Table 1.2). The discovery of the etiology is by far the most difficult part of the diagnostic process; later in this chapter and in several other chapters, we discuss what is currently known about the causation of most of the common orofacial pain disorders.

Table 1.2 Probable etiologies associated with the 30 most common orofacial pain diseases

AIDS, acquired immunodeficiency syndrome; CDH, chronic daily headache; CH, cluster headache; CNS, central nervous system; CTD, connective tissue disease; ddC, dideoxycytidine; ddI, dideoxyinosine; DDNR, disk displacement with no reduction; DDWR, disk displacement with reduction; GVHD, graft-versus-host disease; HIV, human immunodeficiency virus; NSAIDs, nonsteroidal anti-inflammatory drugs; SSRIs, selective serotonin reuptake inhibitors; TMJ, temporomandibular joint.

1.1.C Anatomic Localization and Age Predilection

Another essential component of the differential diagnostic process is to fully understand and document the anatomic localization and extent of the pain site. In most cases this begins by having the patient outline the pain’s outer borders and then pinpoint the pain’s focal source (if one exists). The clinician must also palpate this source to verify it and see if, with simple pressure, the pain can be replicated. Based on the physical signs and symptoms as well as the anatomic location, pattern, and character of the pain, a list of diseases that cause pain in the orofacial region can usually be narrowed down to two or three likely pain disorders. This process is facilitated if, when creating the differential diagnosis list, the clinician has in mind the “age-based” predilections of the painful diseases that occur in the orofacial region. For example, trigeminal neuralgia is far more likely in someone over the age of 50 than under the age of 50.

1.1.D Diagnostic Testing

Appropriate tests or diagnostic–treatment procedures may help narrow the list to the most likely diagnosis; however, due to the subjective nature of pain, there is no test that can measure the intensity of pain, nor any current clinically useful imaging device that can show pain. In most cases, clinicians must use the patient’s own description of the type, duration, and location of the pain to get diagnostic clues. Certain pain-inducing pathologies are visible on a radiograph or a magnetic resonance image (MRI); however, because many are not, we must occasionally use innovative methods to confirm our diagnosis. These innovative methods are discussed in Chapter 10, but here we provide in table form the most frequently used diagnostic methods appro­priate for the 30 diseases considered in this chapter (Table 1.3). More details on the pros and cons of these tests are provided in the various chapters where each disease entity is discussed.

Table 1.3 Confirmatory or exclusionary diagnostic methods

ANA, antinuclear antibody; CT, computed tomography; CNS, central nervous system; CRP, C-reactive protein; CTD, connective tissue disease; DDNR, disk displacement with no reduction; DDWR, disk displacement with reduction; ESR, erythrocyte sedimentation rate; HIV, human immunodeficiency virus; MRI, magnetic resonance imaging; NSAIDs, nonsteroidal anti-inflammatory drugs; OA, osteoarthritis; RF, rheumatic factor; ROM, range of motion; SSRIs, selective serotonin reuptake inhibitors; TMJ, temporomandibular joint.

1.1.E Prevalence of Orofacial Pain

Comparing the age predilection, the anatomic localization, and the character of the patient’s problem with the known prevalence of orofacial pain disorders usually allows the clinician to make a reasonable diagnosis. The reported overall prevalence of general persistent pain in the adult population of the United States is quite high. For example, a Gallup survey of 2002 adults found that approximately 4 of 10 adults (42%) of those polled say they experience pain on a daily basis, while 89% admit to experiencing pain on a monthly basis.² These pains have diverse origins: chronic pain disorders such as arthritis, osteoporosis, diabetic neuropathy, migraine, and fibromyalgia; pain related to cancer; postsurgical pain; and pain caused by accidents and burns. Whether it is cancer pain or noncancer pain, opioid treat­ment of pain is common. For example, 73% of hospitalized patients receiving opioid therapy still reported moderate distress and 75% of postsurgical patients were in either moderate or marked distress.^3,4 When you look more closely at elderly patients (defined as over the age of 65), the prevalence of general persistent pain is much higher than in those under the age of 65. The prevalence of persistent pain in the elderly ranges from 25% to 88%, depending on the definition used and the subset of elderly patients being studied.^5,6 For example, another study conducted telephone interviews of community-dwelling north Floridians (n = 1636) who were over 65 years of age and found that 17.4% reported some form of current or recent (with the last year) orofacial pain.⁷

1.2 Facial Pain Related to Muscle Pain

Muscle pain comes in many forms, from the widespread types such as fibromyalgia to the local and regional forms of myalgia. Myofascial pain and the more generalized fibromyalgia syndrome (FMS) are common chronic pain problems that predominantly affect middle-aged women.^8–11 While local myalgia and myofascial pain are more preva­lent in the middle aged, fibromyalgia increases with age and is substantially more evident in the elderly popula­tion. Each of the myalgia subtypes is discussed in the following subsections. A detailed discussion of these dis­orders and their appropriate management is presented in Chapter 16.

1.2.A Disease 1a: Primary Myalgia

Myalgia can be separated into local and regional, with a distinction between primary and secondary myalgia also made. The term “primary myalgia” indicates that if a biopsy were performed, there would be no microscopic evidence of inflammation. Histologically evident myositis is discussed in Section 1.2.B on secondary myaglia.^12,13 The pain-inducing changes seen in primary myalgia are most likely due to sensitization of muscle nociceptors.

Clinical Criteria

When a direct muscle injury that explains the muscle pain cannot be found and the patient does not have another adjacent pathology in the area that would cause secondary muscle guarding effects (e.g., arthritis of the TMJ or internal derangement of the TMJ), then one of the criteria for a primary myalgia is satisfied. The actual diagnosis of myalgia (all types) requires the following additional criteria to be satisfied: (1) the patient is aware of pain in the muscle on function; (2) this pain must be replicated by palpation; and (3) there is no discernable taut band or trigger point in the muscle that causes pain to radiate on palpation.

Etiology

If a primary myalgia is suspected, the clinician must seek to find the etiology by asking about (1) medications, (2) stress, and (3) parafunctions (both waking and sleeping). If a patient is using psychological stimulant medication or is using a serotonin selective reuptake inhibitor (SSRI), then a medication-induced myalgia would be suspected. The various medications that can induce muscle pain are reviewed in Chapter 19 and are not discussed here. Second, a stress-associated myalgia should be suspected if a patient reports a prolonged increase in environmental (job or personal) stress levels. A discussion of how stress can induce muscle pain without the presence of histologically evident inflammation is given in Chapter 16. With regard to stress, psychological factors have been associated with chronic facial and jaw pain.¹⁴ Third, a parafunction-induced myalgia should be suspected when a patient admits to repetitive oral habits or if such habits are observed. In this case the clinician will typically diagnose a primary myalgia due to parafunction. Sometimes the parafunction is very specific and the pain it produces in the jaw muscles is limited to one or two muscles. Oral parafunctions may be present both during waking and sleeping hours and during specific activities such as chronic gum chewing.¹⁵

Several studies have reported that there is a moderately strong positive association between self-reported clenching and chronic masticatory myofascial pain (MMFP).^16–18 Unfortunately, these studies do not specify whether the clenching is occurring during waking or sleeping periods because to do so accurately would require an actual recording of the jaw motor behaviors over moderately long periods of time (minimum 2 weeks). One study used a case–control design including 83 patients with MMFP, selected from the patients at a hospital dental service, and 100 concurrent controls. Using unconditional logistic regression analysis they found that self-reported clenching–grinding either in association with an elevated anxiety score (OR = 8.48) or an elevated depression score (OR = 8.13) was statistically associated with chronic MMFP. They concluded that tooth clenching, trauma, and female gender strongly contribute to the presence of chronic MMFP even when other psychological symptoms are similar between subjects. Interestingly, grinding-only behaviors, age, and household income and education were not related to chronic MMFP. This report showed no association between tooth grinding and chronic muscle pain, which is in conflict with other studies. For example, one study performed a questionnaire-based epidemiologic cross-sectional study and another used a clinically based case–control design.^19,20 These two studies found a positive relationship between self-reported nocturnal tooth grinding and self-reported jaw pain. This conflict will require additional data to resolve.

1.2.B Disease 1b: Secondary Myalgia Due to Active Local Pathology (E.g., Temporomandibular Joint Disease)

Direct muscle injury is not common in the masticatory system, but when present it can produce a quite dramatic change in normal function causing strong focal pain and severely limited opening; this limitation is due to co-contraction of the openers and closers and is called trismus.²¹

Clinical Criteria

The term “secondary myalgia” implies the presence of some extrinsic direct trauma or local (nonmuscle) pathology that is inducing myalgia.

Etiology

The two most common causes of a secondary myalgia are (1) a traumatic muscle injury and (2) a local nonmuscle pathology that induces a change in muscle function. The most common traumatic cause of a focal myositis in the jaw system is an inadvertent intramuscular injection of local anesthetic during dental treatment. In these cases, the nature of the injury is influenced by the amount of injected material, the type of anesthetic used, and more important, whether a vasoconstrictor such as epinephrine was included in the anesthetic solution. Several authors have described and documented the effect of an inadvertent anesthetic injection into muscle tissue.^22–25 In some cases, acute traumatic trismus can convert to chronic contracture of the involved muscle.²⁶ Other forms of local muscle injury can occur from trauma (e.g., neck musculature can be injured during a low-velocity rear-end collision) that produces a regional cervical muscle strain, which then causes a secondary cervical and sometimes even masticatory myalgia. Current data suggests that the jaw closing and opening muscles themselves are not overstretched or torn during a low-velocity rear-end motor vehicle collision,^27,28 but they may become involved when a guarding–trismus response develops in concert with the injured craniocervical muscles.²⁹ If a direct muscle trauma is suspected as the etiology, then the traumatic event is usually easily identified in the history. Fortunately, most such traumatic injuries are self-resolving without long-term consequences.

When a local pain-inducing pathology is present, localized and even regional myalgia will develop in response. For example, acute TMJ arthritis can cause an associated muscle pain in the masseter and temporalis on the side ipsilateral to the involved joint. The pain in the muscle tissue is secondary, but it may generate an equal or greater degree of tenderness to palpation than elicited by palpating the involved joint. That the nociceptors inside a joint or even inside a tooth can induce a secondary motor reaction in the anatomically adjacent muscle has been clearly demonstrated in the literature.^30,31 The most likely secondary jaw and cervical motor activation occurs with a painful arthritis or internal derangement of the TMJ.³² However, these reactions are also likely to occur with acute pulpal pain, osteomyelitis, or other mandibular bone or soft-tissue infections in the region. When a patient presents with one-sided muscle pain in the absence of trauma or a strong stress or parafunction history, the clinician should carefully examine the TMJ for local disease or dysfunction. When a patient presents with both a local pathologic process and muscle pain that seems to have developed after the pathology began, it would be appropriate to consider that the myogenous process is a secondary myalgia not a primary one. In these cases it is logical and appropriate to manage or minimize the local pathology first and then re-examine the myogenous pain for resolution or persistence.

1.2.C Disease 2: Myofascial Pain (Focal or Regional)

While many consider myalgia and myofascial pain to be similar, the International Association for the Study of Pain Subcommittee on Taxonomy has classified myofascial pain (MFP) as pain in any muscle with trigger points that are very painful to compression during palpation and cause referred pain sensations.³³ Essentially the term myofascial pain is used only when specific criteria are satisfied.

Clinical Criteria

The criteria for myofascial pain are both subjective (history based) and objective (examination based). The three subjective criteria that patients should endorse are (1) spontaneous dull aching pain and localized tenderness in the involved muscle(s), (2) stiffness in the involved body area, and (3) easily induced fatigueability with sustained function. The four objective criteria are (1) a hyperirritable spot within a palpably taut band of skeletal muscle or muscle fascia, (2) reports by the patient, upon sustained compression of this hyperirritable spot, of new or increased dull aching pain in a nearby site, (3) decreased range of unassisted movement of the involved body area, and (4) weakness without atrophy and no neurological deficit explaining this weakness. Many have included the presence of referred autonomic phenomena upon compression of the hyperirritable spot and/or a twitch response to snapping palpation of the taut bands as additional diagnostic criteria.^34–38 However, inclusion of the last criterion is not endorsed by all since it is not a reliably present physical finding.³⁹

Etiology

The common etiologies that cause myofascial pain are the same as those given for myalgia (see Secs. 1.2.A and 1.2.B).

1.2.D Disease 3: Chronic Widespread Pain and Fibromyalgia

Chronic widespread pain and fibromyalgia are quite similar conditions in that the patient has complaints of multiquadrant muscle pain, but only fibromyalgia has an accepted set of specific physical examination criteria. Fibromyalgia affects up to 2% of the population and can start at any age; it is at least 7 times more common in women than in men.⁴⁰ By the time the diagnosis is made, patients have often had symptoms for many years.

Clinical Criteria

Patients with fibromyalgia complain of muscular and sometimes joint pain all over and, by definition, have pain on both sides of the body, above and below the waist, and in both the trunk and extremities. There are specific clinical history and examination criteria that must be met before a diagnosis of fibromylagia is rendered. These criteria, adopted by the American College of Rheumatology (ACR), specify that a diagnosis of fibromyalgia is made when there is widespread pain lasting for at least 3 months accompanied by tenderness at discrete locations.⁴¹ According to the ACR criteria, patients must have at least 11 tender points of a possible 18 but, in practice, the diagnosis can be made in patients with fewer tender points if there is widespread pain and many of the other characteristic symptoms. Patients with fibromyalgia are often tender all over; the presence of tenderness other than at the classic locations does not exclude the diagnosis. These findings suggest and most researchers agree that an aberrant central pain processing mechanism produces a state of sensitized pain perception in FMS.⁴² Because of the widespread muscle and joint pain, fibromyalgia patients usually have poor-quality nonrestorative sleep. They also frequently report irritable bowel syndrome and headaches. Because of the negative effect fibromyalgia has on activities of daily living, it usually induces depression and anxiety, and it often accompanies other chronic painful disorders.⁴³

Etiology

It is likely that patients who develop chronic widespread pain and/or fibromyalgia have a genetic factor that predisposes them to sensitization of the central nervous system (CNS). For the local factors that trigger pain, see Sections 1.2.A and 1.2.B; the common etiologies that cause fibromyalgia are the same as those given for myalgia.

1.3 Facial Pain Due to Derangement and Non-Autoimmune Arthritis or Capsulitis of the Temporomandibular Joint

The second subgroup of conditions is facial />