Pain of the zygomatic arch region is common among patients with orofacial pain, especially in those with temporomandibular disorder-related pain of a myogenic origin. Since zygomatic arch pain may occur due to various causes other than muscle pain, appropriate diagnosis and treatment planning is essential to ensure its successful management. Unfortunately, zygomatic arch pain has not been handled as an independent clinical feature until now, and studies have mainly focused on pain resulting from trauma and surgical procedures.

We describe 7 independent cases, all of which presented with the identical chief complaint of pain in the zygomatic arch region. However, the underlying causes were different for each, being myofascial pain, myositis, tooth crack, dental caries, sinusitis, neuropathic pain, and salivary gland tumor respectively. In this case report, the clinical features of each case are investigated and diseases to be considered in the diagnostic process are suggested, along with the diagnostic modalities (including computed tomography and magnetic resonance imaging) that can lead to the appropriate final diagnosis.

Zygomatic arch pain is a common complaint encountered in the orofacial pain clinic but may lead to misdiagnosis. Clinicians must have in-depth knowledge of the possible differential diagnoses and evaluation tools.

Many patients visit a pain clinic with the complaint of orofacial pain associated with the zygomatic arch region. However, the pain that the patient describes may not always originate from the masseter muscle that is attached to the medial side and lower border of the zygomatic arch bone. The zygomatic arch is surrounded by various structures, including masticatory muscles (masseter, temporalis, lateral pterygoid, and medial pterygoid muscle), trapezius muscle, splenius capitis muscle, anterior digastric muscle, posterior digastric muscle, coronoid process, temporomandibular joint (TMJ), maxillary teeth, and the maxillary sinus, all of which can produce pain in the zygomatic arch area. Referred pain from remote areas may also present in the same region. In this case, the source of pain must be identified and targeted to determine appropriate treatment and obtain successful results.

Referred pain is the recognition of pain sensation in areas other than that of the original noxious stimulation. Referred pain can occur from both visceral and somatic structures[1]. Somatic referred pain is recognized at the site that shares the same segmental innervation as the source of the pain[2]. Whatever the cause of the symptoms, secondary hyperalgesia frequently occurs in the referral area[3]. Studies have shown that if the source pain lasts for more than a certain amount of time, the pain in the referral area does not disappear even when the original cause of pain is removed[4]. This suggests that pain in the referral area can afflict the patient chronically, persisting beyond removal of the original pain source through treatment. The orofacial region is a common site for referred pain and is frequently the cause of misdiagnosis and confusion for both the clinician and patient[5,6]. Therefore, understanding referred pain, locating the pain source, and treating both the original pain source and referred pain-related symptoms are essential for the orofacial pain specialist to successfully reduce the patient's overall pain level.

This review examines the various diagnostic results of patients who visited our orofacial pain clinic with a chief complaint associated to pain in the zygomatic arch region. Since accurate differential diagnosis is essential for the successful prognosis of treatment, the clinical characteristics and diagnostic processes of 5 case categories (7 patients, Table 1) are presented herein. In addition, other possible diagnoses of orofacial pain are analyzed through previous literature with the purpose of providing the readers with a comprehensive review of orofacial pain associated with the zygomatic arch region.

Often, patients complaining of pain of the zygomatic arch region seek the orofacial pain clinic, and specialists too quickly determine the cause of pain as the masticatory muscles based on empirical evidence[12]. This may be true in many cases, but this case series shows that various conditions may present as orofacial pain associated with the zygomatic arch and accurate diagnosis may be further hindered due to coincidence of masticatory muscle pain along with other ailments. As shown in this case series, myositis, odontogenic pain, neuralgia, sinusitis, and salivary gland tumor are other possible causes of orofacial pain that could be encountered in the clinic. Correct differential diagnosis is critical since treatment planning and ultimately the patient’s prognosis depend on it.

Myofascial pain is characterized by localized muscular pain with a tight, sensitive focal area called the trigger point[13]. Clinical features of myofascial pain include pain at rest, increased pain with function, and limitation of muscle movement. Patients generally describe the pain as deep and aching[14]. The trigger point can induce central excitatory effects, and referred pain often appears in a predictable pattern depending on the location of the trigger point[15]. Referred pain appears in the zygomatic arch region when trigger points located in the temporalis, masseter, lateral and medial pterygoid muscles are pressed. Therefore, if the pain source is originally in the above-mentioned muscles, pain in the zygomatic arch area may be present. Notably, referred pain in the zygomatic arch region has been reported as most frequently caused when trigger points of the lateral pterygoid muscle are compressed[16]. Therefore, when the patient complains of pain in the zygomatic arch region, the masticatory muscles should be evaluated carefully to identify the true source of pain.

The lateral pterygoid muscle may be easily omitted in the evaluation process to find the cause of zygomatic arch pain since clinicians tend to palpate only the muscles that can be approached extra-orally. However, it is necessary to perform intra-oral palpation and functional manipulation to investigate all candidate muscles that could be causing the zygomatic arch pain. Functional manipulation of the lateral pterygoid muscle can be done by allowing the patient to protrude the jaw against resistance provided by the clinician. Similarly, when myositis inflicts the above-mentioned muscles, zygomatic arch pain may be present. Infection, trauma or persistently elevated muscle tension may cause inflammation. Myositis can be divided into infectious and non-infectious subtypes. In non-infectious myositis, prolonged muscle pain may lead to a change in the central nervous system, thus resulting in centrally mediated myalgia which is associated with neurogenic inflammation. However, infectious myositis occurs with bacterial or viral infections and is accompanied by typical signs of inflammation, such as swelling, rupture, and fever[13].

In our case of myositis, ORN caused by radiotherapy resulted in inflammation of the surrounding muscles, including the lateral pterygoid and temporalis muscle. The fact that the patient received radiotherapy very long ago hindered the diagnostic process, but reports that ORN had occurred 3-15 years after radiation treatment should be considered[17]. In the above case, both the initial diagnosis of masticatory muscle pain and second diagnosis of neuropathic pain based on only clinical examination and plain radiographs were wrong and only after advanced imaging, including MRI and CT, were done was a correct diagnosis of ORN and myositis made. Therefore, detailed history taking is important in the diagnosis of patients who complain of zygomatic arch pain, and appropriate imaging including CT and/or MRI should be performed, especially when the clinical symptoms are not typical of a given diagnosis and the patient does not respond well to conventional treatment approaches. The diagnosis of ORN is generally based on the identification of symptoms such as odor, headache, purulent debris, and intermittent bleeding. CT and endoscopy are recommended as additional diagnostic tools[17]. The clinical symptoms of the patient may have been caused by ear infections that led to the enhancement in the mastoid process region in the MRI; however, the otorhinolaryngologist did not find any evident symptoms through ear inspections, so the mastoid process lesion was considered secondary to the lateral pterygoid muscle inflammation. Treatment of myofascial pain is generally conservative including medication, physical, and behavioral therapy[13]. On the other hand, when the pain is due to myositis caused by radiation therapy as presented in this report treatment with antibiotics may be called upon and a multidisciplinary approach may be necessary depending on the source of infection.

Odontogenic pain of the upper teeth may cause zygomatic arch pain. For accurate differential diagnosis, attention should be paid to the characteristics of the patient's pain. Patients with muscle pain generally feel a dull ache following the muscle distribution. Odontogenic pain worsens with heat and cold stimuli, and reacts to percussion[18]. A cracked tooth, identified through intraoral examination, can be further evaluated by vitality testing[19] with positive responses and percussion in an axial direction with negative responses[20]. The 2 cases we introduced were each caused by tooth crack and secondary caries. These cases are often difficult to diagnose since symptoms are unclear radiographically and clinically in their early stages. Diagnostic anesthesia is a very useful method that may be applied in such situations[21]. In the case of odontogenic pain, pain is dramatically relieved following anesthesia of the causative tooth. The second case of odontogenic pain was especially difficult to diagnose because of concomitant muscle problems. Even in such a situation, diagnostic anesthesia could be successfully applied to find and solve the cause of pain in the zygomatic arch region.

The maxillary sinus is part of a series of paranasal sinuses, that includes the frontal, ethmoid, and sphenoid sinuses. Maxillary sinusitis causes a constant burning pain, with zygomatic and dental area tenderness[22]. Maxillary sinusitis causes continuous pain of a dull, aching, and tender quality, with mild to moderate severity, and could be unilateral or bilateral[23]. Other symptoms include postnasal drip, nasal congestion, purulent anterior rhinorrhea, foul smell or taste, and fatigue[24]. Radiographic examinations such as CT or MRI can play a key role in the diagnosis of maxillary sinusitis[23]. In chronic maxillary sinusitis, it is recommended that imaging be performed requisitely because symptoms may not be characteristic. The reported patient had already visited various hospitals for 2 years before the first visit to our hospital, with the aim of obtaining a definite diagnosis. In our case, symptoms such as headache and pain on pressure of the zygomatic arch and masseter region caused confusion. However, the diagnosis of sinusitis was confirmed by CT and the patient did not complain of persistent pain once the sinusitis was treated, making it possible to rule out neuropathic pain of the superior alveolar nerves secondary to long-term sinus inflammation.

Neuropathic pain should be considered as a possible cause of zygomatic arch pain since the maxillary branch of the trigeminal nerve is distributed in the zygomatic arch region. A good illustration would be infraorbital neuralgia, which is caused by a branch of the maxillary nerve and is known to be accompanied by zygomatic arch pain[25]. Previous report showed that such pain could be temporarily relieved by infraorbital nerve block and controlled by pregabalin intake after failing with several drugs, including carbamazepine and amitriptyline[25]. The diagnosis of neuralgia is primarily based on patient history. Patients with neuralgia mainly complain of sharp, shooting, stabbing and electric shock-like pain which appears unilaterally in most cases. In the case of TN, pain is triggered by non-painful stimulation, such as soft touching of the affected area or even speaking[18]. However, in some patients, the paroxysms are less intense, and may appear as a deep dull or burning sensation. Response to drugs can also be a key to diagnosis. Neuralgia responds to drugs such as carbamazepine or tricyclic antidepressants without showing significant response to NSAIDs. In addition, MRI should be performed to rule out secondary neuralgia with an organic lesion affecting the nerve[27].

Salivary gland tumor is another possible cause of zygomatic arch pain. In our case, the patient had already undergone surgery and radiation therapy for salivary gland tumors; therefore, the initial diagnosis was incorrectly made as myofascial pain with limited mouth opening due to surgery and radiation therapy. However, there was no response to physical therapy and medication, and the pain was relatively strong compared to the general pain intensity of muscle pain[28]. Maximum mouth opening was also severely limited to 18 mm. Such clinical characteristics called for a consultation to the department of otorhinolaryngology to reassess the surgical site, and recurrent salivary gland tumor was confirmed through positron emission tomography and MRI. Malignant salivary gland tumors are very rare and the most common tumor site is the parotid gland[29]. Clinical features include pain, facial nerve involvement, and parapharyngeal and palatal fullness. In addition, trismus and skin ulceration may appear in severely advanced malignancies[30,31]. Therefore, when patients with zygomatic arch pain show restricted mouth opening simultaneously with the above-mentioned symptoms, CT and MRI should be performed and appropriate consultations should be made.

Other possible diagnoses related to zygomatic arch pain have been reported in previous literature. In TMD patients with temporal tendinitis, 49% complained of referred pain in the zygomatic arch region[32]. A case report presented a patient with temporal tendinitis showing continuous squeezing pain in the zygomatic arch and temporalis regions, with increased pain during mandibular movements[33]. The diagnosis of temporal tendinitis is based on clinical features of tenderness and/or pain at the tendon insertion site and temporalis muscle, restricted mandibular movement, and the reduction of pain with local anesthesia of the originally afflicted site. Elongation of the coronoid process may appear on radiographic examination but its relation to the diagnosis is still controversial[34]. Temporal tendinosis has also been cited as a cause of orofacial pain in recent literature so should be considered when the patient complains of pain occurring in the zygomatic arch region[35]. Tendinitis is inflammation located in the tendon, while tendinosis is a degenerative state caused by persistent overuse and lacks signs of inflammation both clinically and histologically[36]. Tendinosis is commonly misdiagnosed as tendinitis. Temporal tendinosis is typically accompanied by chronic pain of the orofacial region and stiffness in the temporalis muscle area that is exacerbated by jaw function. Mouth opening limitation can be observed in certain cases. Temporal tendinosis can be easily overlooked in the differential diagnosis of pain in the zygomatic arch region because of the anatomic complexity of the area. Since palpation shows low sensitivity and specificity in its diagnosis imaging, especially ultrasound should be considered when the presence of temporal tendinosis is questioned[35].

Referred pain due to coronary insufficiency may also appear in the mandible, zygomatic arch, and temporal region[37]. A case was reported where facial pain, including the zygomatic arch, was caused by myocardial infarction[38]. A previous review summarized that referred pain due to cardiac origins may appear in the maxilla, mandible, zygomatic arches, submandibular, neck, temporalis muscle and teeth regions[39]. The underlying mechanism of such pain referral is complicated and it would be difficult to locate a single transmission route, but cardiac etiology could be another possibility when the cause of orofacial pain is not clinically evident[40].

Posterior scleritis can also cause zygomatic arch pain[36]. Posterior scleritis is rarely known to cause facial pain. The main area of pain is periocular but may also appear as referred pain in the forehead, zygomatic arch, and temple region. The pain is generally described as increasing with ocular movement. Visual disturbances and other ocular signs are also accompanying. Visual loss is a critical complication of posterior scleritis that may occur[41], so posterior scleritis should be suspected and measures for accurate diagnosis should be taken when a patient with zygomatic arch pain complains of concomitant ocular symptoms, to avoid irreversible outcomes.

Although relatively rare, various neoplasms of the maxillofacial region could also be another possibility. In osteochondroma affecting the coronoid process, pain was not a common symptom, but approximately 10% of the cases reported facial pain[42]. With peripheral osteoma of the zygomatic arch, some patients complained of pain[43]. When the complaint of pain in the zygomatic arch region is accompanied by swelling, facial asymmetry, and limited mouth opening, appropriate imaging should be performed with the above diagnoses in mind.

This is the first case series report to describe various cases of orofacial pain with the zygomatic arch region as the main pain focus. Although this report has inherent limitations as a case series and retrospective analysis, it provides the clinician with a comprehensive summary of possible differential diagnoses by concentrating on the patients’ identical chief complaint – pain in the zygomatic arch region – then inversely providing the full diagnostic processes for its various underlying diseases.

Zygomatic arch pain is commonly reported by patients visiting the orofacial pain clinic and is majorly accepted to be caused by masseter muscle pain. But a variety of conditions may present as orofacial pain in the zygomatic arch region, including life-threatening diseases such as salivary gland tumors. Therefore, accurate differential diagnosis is essential for good prognosis and the prevention of complications due to misdiagnosis. Clinicians should have in-depth knowledge of diseases that may cause orofacial pain and know how to accurately assess structures with various modalities, such as CT and MRI. Diagnostic anesthesia can also play an important role in locating the cause of pain.