Facial Pain
Alaa Abd-Elsayed
Pamela J. Hughes
Ahmed M.T. Raslan
Facial pain syndromes are common in clinical practice. Many of these syndromes are also unique, given the complex anatomy and specialized sensory innervation of the head, face, and neck. The complexity of the anatomy can pose diagnostic challenges when endeavoring to treat facial pain syndromes.
The common descriptive terms for facial pain complaints are frequently misleading. To avoid confusion, clinicians should be familiar with the International Headache Society’s Diagnostic Classification for Head, Face, and Neck Pain Disorders (Table 67.1).
The aforementioned grouping of diagnose(s) is a rather exhaustive differential diagnosis of facial pain. This includes acute and subacute conditions that affect a vast majority of the structures of the human head. This would include ocular, nasal, sinus, dental, oral, muscular, mucosal, and any other causes specific to the region of the head and face.
Although such a list is good for an all-encompassing reference, it is not necessarily helpful for pain practitioners who deal mostly with chronic pain conditions. In this chapter, the focus is on chronic pain conditions that would present as facial pain. Because the primary differential diagnosis of facial pain is trigeminal neuralgia and the nociceptive pain pathway responsible for facial pain, conditions that present in a similar fashion to trigeminal neuralgia or could be misdiagnosed as such are discussed in detail here.
TABLE 67.1 International Headache Society International Classification of Headache Disorders1 | ||||||||||
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Trigeminal and Other Cranial Nerve Neuropathic Conditions
TRIGEMINAL NEUROPATHY
Trigeminal neuropathy is a spectrum, the earliest of which is classically called trigeminal neuralgia. Because the most classic description of trigeminal neuralgia is episodic, sharp shooting pain without any detectable sensory or motor deficit, there are also other forms of trigeminal neuropathic pain that signify a higher degree of neuropathy. The best description of the spectral nature of trigeminal facial pain is found in the classification offered by Burchiel et al.2,3 in 2003 and 2005.
In that classification, pain is classified based on the understanding of the pathophysiology of neuralgia (Table 67.2).
Trigeminal Neuralgia Type 1
This represents the classic description of trigeminal neuralgia in its purest form; it is idiopathic, sharp, shooting, electrical shock-like, episodic pain lasting several seconds, with pain-free intervals between attacks. This diagnosis is fairly straightforward, and most neurosurgeons are familiar with this clinical entity. The condition is caused usually by a vascular compression near the root entry zone because it is the junction of the central and peripheral myelin that renders that zone susceptible to the pathology. Vascular compression leads to demyelination, which in turn leads to ectopic action potential generation that is suspected to allegedly drive the sharp lancinating episodes of facial pain. A full description of the pathophysiology of pain triggering is best described by Devor in 2002 as the ignition hypothesis.4,5
Trigeminal Neuralgia Type 2
This is still a variant of the classic idiopathic trigeminal neuralgia; however, the crucial feature of this condition is the presence of dull aching or background pain for more than 50% of time. This represents a form of trigeminal neuralgia with more evidence of sensory neuropathy compared to type 1. Some of these patients do progress from type 1, and some present as such on initial presentation. Several studies suggest that surgical treatment for trigeminal neuralgia is more successful and durable in patients with trigeminal neuralgia type 1 compared to type 2.6 It is fairly common to have a normal bedside sensory examination testing in cases of idiopathic trigeminal neuralgia regardless of the type.
Symptomatic Trigeminal Neuralgia
In contrast to idiopathic forms of trigeminal neuralgia, this is not an idiopathic form, it is caused by either a diagnosed demyelinating disorder such as multiple sclerosis, a tumor, a vascular malformation, or other structural pathology leading to compression of the trigeminal root entry zone, other than the
vascular compression described in idiopathic forms. It is noteworthy that clinically patients may present in either a type 1-or type 2-like presentation; however, constant dull aching pain (type 2 like) is more common in patients with symptomatic trigeminal neuralgia.
vascular compression described in idiopathic forms. It is noteworthy that clinically patients may present in either a type 1-or type 2-like presentation; however, constant dull aching pain (type 2 like) is more common in patients with symptomatic trigeminal neuralgia.
TABLE 67.2 Classifications and Pathophysiology of Neuralgia | |||||||||||||||||||||
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Neuropathic Trigeminal Neuralgia
In this entity, the degree of trigeminal neuropathy is more advanced compared to idiopathic trigeminal neuralgia; there is an objective sensory loss in the distribution of the trigeminal nerve and it is associated with classic manifestations of neuropathic pain including but not limited to allodynia, hyperalgesia, and burning pain. Neuropathic trigeminal neuralgia is usually caused by either intentional or unintentional injury to the trigeminal nerve. Examples of unintentional injuries would include trauma; postdental injection; postprocedural in maxillofacial surgeries; skull bases surgery; ear, nose, and, throat (ENT) surgery; or poststroke. Examples of intentional injuries include trigeminal neuropathy following neurosurgical ablation of the one or more branches of the trigeminal nerve for the purpose of alleviation of pain. Spontaneous neuropathic trigeminal neuralgia had been also described, albeit, a rare condition.7
Postherpetic Trigeminal Neuralgia
Postherpetic trigeminal neuralgia is the condition that follows herpes zoster viral infection to the trigeminal ganglion. It is a more severe form of neuropathy manifested by significant allodynia, hyperalgesia, and burning dysesthesia. It commonly affects the first division of the trigeminal nerve.
Deafferentation Trigeminal Neuralgia
Deafferentation trigeminal neuralgia, otherwise known as anesthesia dolorosa, is the most severe form of neuropathy and trigeminal neuralgia. The features of this pathology suggest a marked sensory loss or even corneal anesthesia in severe cases. Unfortunately, this is an iatrogenic condition that is induced by surgical interventions to denervate the trigeminal distribution. It is common with techniques such as rhizotomy or alcohol denervation and less common (or require repeated exposure) after techniques with rather smaller quantifiable ablation such as radiofrequency rhizotomy, glycerol rhizotomy, balloon compression, or radiosurgery.
Atypical Facial Pain
In this particular classification, atypical facial pain refers to somatoform disorder, in which a psychological disorder can be unequivocally diagnosed. Obviously, this is a difficult condition to treat and would be a contraindication to interventional therapies.
Treatment of various forms of trigeminal neuralgia is mentioned elsewhere in this textbook, but the degree of neuropathy determines the possible reversibility and therefore dictates the treatment options. Medical treatments for most of cranial nerve neuropathy-related pain is medical at first with medications such as carbamazepine, gabapentin, and topiramate. Should medical treatment fail, interventional therapies are introduced, and these are introduced based on the degree of neuropathy. As such, early neuropathy such as trigeminal neuralgia type 1 would benefit from a potentially curative option such as microvascular decompression, whereas postherpetic neuralgia requires advanced interventions such as neuromodulation of the central nervous system.
GLOSSOPHARYNGEAL NEURALGIA
Glossopharyngeal neuralgia (GN) is a rare condition in which patients experience paroxysmal episodes of pain along the auricular and pharyngeal branches of both the glossopharyngeal and vagus nerves. Patients will often complain of severe, lancinating pain “attacks” along one side of the throat, with occasional radiation to the ear, that are often precipitated by swallowing, chewing, coughing, or yawning.8 It can be particularly debilitating when the vagus nerve is involved as patients may experience loss of sympathetic tone that can lead to syncope and seizures in up to 10% of the cases.9
GN is most often caused by neurovascular compression at the root entry zone of the brainstem—most often, it is the posterior inferior cerebellar artery that is responsible for the compression, although the anterior inferior cerebellar artery (AICA) has been documented as well.10 With an incidence of just 1% when compared to its better known counterpart, trigeminal neuralgia, GN is notoriously hard to diagnose.11 Given this diagnostic dilemma, high-sensitivity, high-specificity magnetic resonance imaging (MRI) is recommended to rule out any other potential causes such as neoplasm or an elongated styloid process.10
Treatment is initially medical, as with most cranial neuralgias, and if this fails, surgical decompression or sectioning may be very effective in alleviating pain.12 Ruling out mimicking conditions such as Eagle syndrome is critical prior to administering an interventional therapy.
NERVUS INTERMEDIUS NEURALGIA
Nervus intermedius neuralgia (NIN), also known as geniculate neuralgia, is a rare pain condition characterized by paroxysmal, deep ear pain. Patients commonly describe the pain as “being stabbed in the ear with an icepick.” These attacks can be debilitating and socially isolating. The posterior wall of the auditory canal as well as the superficial ear drum are common trigger zones for the paroxysms, for example, by loud noises or cold wind.13 Sensory innervation to the skin of the external ear and auditory canal is complex, including contributions from cranial nerves (CN) V, IX, and X; the nervus intermedius (NI); and upper cervical dorsal roots.14 This complicated innervation leads to confusion about the culprit nerve in primary otalgia and contributes ultimately to confusion in diagnosis. Medical treatment is the first-line therapy for this condition, and, as with other cranial neuralgia, surgical decompression or section can be effective.15
Odontogenic and Temporomandibular Joint Disorders
ODONTOGENIC PAIN
Facial pain emanating from an odontogenic source can be a challenge to distinguish from other causes of facial pain. This section guides the clinician to identify potential sources of odontogenic pain, understand the different characteristics of those sources of pain, and ultimately provide for a differential diagnosis. To fully understand the mechanisms to which odontogenic pain arises, a review of dental anatomy and the process of how dental pathology progresses is required.
The normal anatomy of a tooth is characterized by three layers (from the surface to the middle of the tooth): enamel, dentin and dental pulp on the crown of the tooth and cementum, and dentin and dental pulp on the roots of the teeth (Fig. 67.1).
The dental pulp is the generative part of the tooth and is made up of connective tissue and generative cells called odontoblasts. This part of the tooth is also innervated and when insulted causes tooth pain. Dental caries is the typical etiology of dental pain and begins by invading the enamel, progressing to the dentin, and then, if unrestored by a dentist, will progress to invade the pulp, seeding the pulp tissue with harmful bacteria that causes infection and inflammation. This leads to an acute episode of pain and then can lead to abscess formation. As the dental caries progresses through the layers of the tooth, the characteristics of dental pain change, as does the dental or pulpal diagnosis. Once the dental pulp becomes necrotic, the pain may subside, but the necrotic tissue will act as a substrate for pathogenic bacteria that then can cause spread of infection to surrounding tissues.
 FIGURE 67.1 Normal tooth anatomy. |
A second source of odontogenic pain stems from the tissues surrounding the dentition. Periodontitis is a chronic, periradicular disease characterized by inflammation of the gingiva causing soft tissue attachment loss and bone loss surrounding the tooth. In its early stages, the process may be painless but, if untreated, culminates in mobility of teeth and ultimately tooth loss. The degree of pain associated with periodontal disease in the absence of abscess formation is typically mild and not limited to one particular area of the mouth. It is also important to note that periodontal disease is an inflammatory process that is associated with other systemic, chronic disease such as diabetes.
Pericoronitis is a type of gingival inflammation that typically occurs around an erupting or partially erupted third molar (wisdom tooth). The inflammatory response in acute pericoronitis can be significant causing severe pain and trismus and may lead to severe cellulitis and abscess spreading to the deep spaces of the neck and posterior oropharynx.
Steps for Diagnosis
A good clinical exam begins with a thorough history. The timing, location, and characteristics of the patient’s pain must be investigated. A head and neck exam should include palpation of the neck, facial bones, muscles, and soft tissues. The temporomandibular joint (TMJ) should also be included in the head and neck exam and is discussed in another section in this text. Any asymmetries or swellings should be noted, and in the presence of pain, cellulitis or abscess should be suspected. Tenderness to the muscles of mastication without swelling or dental findings should lead the clinician down the path of myofascial origins. The oral examination should include inspection of the dentition, oral mucosa, tongue, floor of the mouth, and the oropharynx.
Dental Findings
The clinician should look for presence of dental disease including dental caries, fractured teeth, or mobile teeth. Dental caries is characterized by the presence of dark areas of the tooth that have invaded or cavitated the enamel (Fig. 67.2).
Stains may sometimes mimic dental caries but will not exhibit loss of tooth structure. In general, the more tooth structure that is involved, the more invasive the decay and the closer to invasion of the pulp causing pain. The decay may start on
the occlusal surface of the tooth, between the teeth, or at the gingival cervical margins. If the decay begins between the teeth, the caries may not be easily identified clinically and may require radiographic evaluation. Teeth with periapical or pulpal inflammation many times will be tender to percussion and will elicit a more painful response then percussion of the surrounding, unaffected teeth. Additionally, the same teeth may elicit painful response to thermal stimulation compared to the surrounding dentition. The degree to which these findings are positive leads to a diagnosis of reversible or irreversible pulpitis (Table 67.3). Mobility of a tooth in the presence of pain may indicate a periapical abscess, or chronic periodontitis. An abscess typically will be limited to one tooth or one area of the mouth, where in chronic periodontitis, multiple teeth usually are affected in several areas of the mouth.
the occlusal surface of the tooth, between the teeth, or at the gingival cervical margins. If the decay begins between the teeth, the caries may not be easily identified clinically and may require radiographic evaluation. Teeth with periapical or pulpal inflammation many times will be tender to percussion and will elicit a more painful response then percussion of the surrounding, unaffected teeth. Additionally, the same teeth may elicit painful response to thermal stimulation compared to the surrounding dentition. The degree to which these findings are positive leads to a diagnosis of reversible or irreversible pulpitis (Table 67.3). Mobility of a tooth in the presence of pain may indicate a periapical abscess, or chronic periodontitis. An abscess typically will be limited to one tooth or one area of the mouth, where in chronic periodontitis, multiple teeth usually are affected in several areas of the mouth.
 FIGURE 67.2 Dental caries. (Source: Anatomical Chart Company. Disorders of the Teeth and Jaw Anatomical Chart, 2004.) |
TABLE 67.3 Characteristics of Facial Odontogenic Pain by Dental Diagnosis | ||||||||||||||||||||||||||||||||||||
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Oral Soft Tissue Findings
The oral mucosa, gingiva, tongue, floor of mouth, and oropharynx should be inspected and palpated for any masses, ulcerations, bleeding, suppuration, or swelling. Areas of acute inflammation will typically be painful and characterized by erythema. If the inflammation and pain is in the area of a carious tooth, an acute inflammatory process should be suspected (pulpitis or acute abscess). Any fistulas present on the gingiva indicate chronic periapical abscess and a necrotic tooth. These are not necessarily painful, but at some point, prior to the fistula formation, may have been a source of pain to the patient. Any suppuration emanating from the gingival crevice of a tooth or multiple teeth in the presence of mobility suggests severe, chronic periodontitis. The gingiva, in this instance, may bleed easily when manipulated.
Most dental pain is limited to the general area of the offending tooth. Pericoronitis and pain secondary to third molars may be more precarious and generalized to the face, jaw, and ear on the affected side. When severe, the patient will exhibit trismus and may have signs of cellulitis.
Radiographic Examination
Dental radiographs in conjunction with clinical findings are needed for definitive diagnosis in most cases. Dental caries are characterized by radiolucencies within the tooth structure. The depth of invasion of the decay will most likely correlate with the level of reported pain.
Periapical pathology indicating pulpal invasion and necrosis may reveal a widened periodontal ligament (PDL) and possible radiolucency at the apex of the tooth. Bone levels below the cementoenamel junction (CEJ) of the tooth indicate periodontal disease (Fig. 67.3).
Evaluating for odontogenic causes of pain should be ruled out when the patient presents with facial pain. Performing a thorough history and clinical exam should lead the clinician to a reasonable suspicion and differential diagnosis; however, a basic understanding of the pathologic process and clinical signs and symptoms of dental disease is helpful in identifying the causes of the odontogenic origin and progression of disease (see Table 67.3).
TEMPOROMANDIBULAR DISORDERS
TMJ disorders are considered the most common musculoskeletal disorders that cause orofacial pain.16 These disorders can typically be separated into two entities: myofascial pain disorders and interarticular disorders (internal derangements). Although these two entities can, and many times do coexist, they have very specific pain patterns that characterize each process. It is important for the clinician to understand the differences, as treatment of these two groups may vary widely. Israel17 defines internal derangement as a condition in which there are damaged intra-articular tissues leading to disturbances in the biomechanical functioning of the TMJ. Fricton18 describes myofascial pain as a regional muscle pain disorder
characterized by localized muscle tenderness, limited range of motion, and regional pain.
characterized by localized muscle tenderness, limited range of motion, and regional pain.
 FIGURE 67.3 Bone levels (red line) below the cementoenamel junction of the tooth, indicate periodontal disease. |
As with any pain disorder, recognition and diagnosis starts with taking a thorough history. Elements specific to temporomandibular disorder (TMD) include the following: severity and character of pain, time of onset, factors that exacerbate the pain or factors that decrease pain, history of trauma or other temporal event, progression of the pain over time, history of joint noises, functional impairment, or range of motion issues. Additionally, quality-of-life questions such as work or life stressors, habits such as bruxism, history of depression, chronic pain, anxiety, or other mental health issues should be addressed as these may contribute to the development of myofascial pain/TMD, or may develop as a result of these disorders.19
Clinical exam should begin with inspection of the face to look for jaw relationship discrepancies including asymmetry, retrognathia, or prognathism. Palpation of the facial, cervical, and occipital musculature should be performed, noting any discomfort to palpation and radiation of that pain within a referral zone of the muscle. Additionally, palpation of muscle bands and firm, localized nodules, or “trigger points” should be noted.3 Palpation of the lateral poles of the mandibular condyle, just anterior to the tragus of the ear, should be performed. Any pain on palpation should be noted. The clinician should also palpate the condyles while the patient performs mandibular movements (opening and closing, lateral excursive movements, and protrusion of the jaw). During this, the clinician should note any clicking, popping, or grinding sensations. Some would advocate for listening with a stethoscope over the joint as the patient performs the aforementioned movements and documenting any joint noises. Range of motion measurements should be obtained. Normal mandibular opening is typically 40 to 45 mm, measured between the incisal edges of the upper and lower incisor teeth. The clinician should also observe for any deviations upon opening. Deviations on opening and the inability to move the jaw laterally either to the right or left should be noted.
Myofascial pain is typically characterized by pain in the muscles of mastication and may exhibit bands and/or trigger points and typically have a zone of referred pain surrounding the tender point.18 The characteristics are summarized in Table 67.4.
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