Myofascial Pain with Referral from the Anterior Digastric Muscle Mimicking

OROFACIAL PAIN Myofascial pain with referral from the anterior digastric muscle mimicking a toothache in the mandibular anterior teeth: a case report Mythili Kalladka, BDS, MSD/Muralidhar Thondebhavi, MD, CCT, MBA/Sowmya Ananthan, BDS, DMD, MSD/ Gautam Kalladka, BDS, MDS/Junad Khan, BDS, MPH, MSD, PhD

Background: Non-odontogenic toothaches often present as a Amitriptyline 10 mg once daily was prescribed for 1 month. In diagnostic dilemma to clinicians. Myofascial pain with referral addition, she was advised home care instructions to control from the trigger points in the masticatory muscles are one of the predisposing, perpetuating, and precipitating factors, and given common causes of non-odontogenic toothaches. However, there home care exercises, a hard joint stabilization splint, physiother- are limited reports of myofascial pain from the anterior digastric apy, and postural re-education. Conclusion: Non- odontogenic muscle referring pain to the mandibular anterior teeth and mim- toothaches may be multifactorial. The case presented empha- icking odontogenic pain. Case presentation: A case of non- sizes the importance of a comprehensive evaluation to differen- odontogenic toothache in the mandibular anterior teeth due tiate odontogenic pain from non-odontogenic pain. Irreversible to myofascial pain with referral from trigger points in the anterior dental procedures should be instituted after an accurate diagno- digastric muscle is presented. The patient had significant relief sis and multidisciplinary management may be required in com- with a trigger point injection of the anterior digastric muscle. plex cases. (Quintessence Int 2020;51: 56–62; doi: 10.3290/j.qi.a43615)

Key words: anterior digastric muscle, myofascial pain, pain, temporomandibular disorder, trigger point

Non-odontogenic toothaches often present as a diagnostic palpated when using the myofascial examination protocol. challenge to clinicians. The clinical picture is confusing and the Spreading pain may also be present.”2 Referred pain from a diagnosis is often elusive. Multiple dental procedures are often myofascial trigger point is defined as “pain arising from a attempted, presuming the pain to be odontogenic in nature. trigger point, but felt at a distance often remote from the Myogenous temporomandibular disorders (TMD) com- source.”3 The trigger points in different muscles have docu- prise a significant proportion of the cases of non-odontogenic mented reproducible patterns of referral; primarily related toothache,1 although the exact epidemiologic data are not to their site of origin.3 The pattern of referred pain from trig- available. The diagnostic criteria for TMD (DC/TMD) for clinical ger points is often distant from the site of the trigger point and research applications broadly classifies myogenous TMD and may not entirely coincide with the peripheral nerve dis- into local myalgia, myofascial pain, and myofascial pain with tribution or dermatomal segment.3 A trigger point is defined referral.2 The DC/TMD criteria describes myofascial pain with as a “hyperirritable spot in a skeletal muscle that is associated referral as “pain of muscle origin that is affected by jaw move- with a hypersensitive palpable nodule in a taut band.”2-4 The ment, function or parafunction and replication of this pain oc- patient’s complaints of pain are replicated when the muscle is curs with provocation testing of the masticatory muscles and examined using the examination protocol by DC/TMD cri- with referral of pain beyond boundary of the muscle being teria with pain referral beyond the muscle being tested.

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Myofascial pain with referral is confirmed by the presence of medications were administered for a period of 3 weeks. The trigger points, pain referral to distant sites characteristic for patient did not report any side effects at the dose administered. each muscle, twitch response at the site, and reproduction of The medications did not have any effect on the pain. the patient’s pain complaint. It may also be accompanied The patient was advised to have a removable partial den- by motor dysfunction and autonomic symptoms.2-5 In many ture in the area of the missing mandibular anterior teeth. instances the pain may be referred to the maxillary and/or During the course of the dental treatment, the patient devel- mandibular teeth. The characteristic referral patterns of the var- oped tenderness in her jaw and was referred to an oral surgeon. ious masticatory and accessory muscles have been described in A soft night guard was fabricated. She had a mild reduction in detail by Simons et al.3 pain with the soft night guard. She was then referred to a pain Presented is a case of non-odontogenic toothache in the physician who in turn referred her to the Orofacial Pain Center. mandibular anterior teeth due to myofascial pain with referrals Investigations ordered by previous dental practitioners and from trigger point in the anterior digastric muscle, and the physicians included an panoramic radiograph, full-mouth management is described. radiographs, temporomandibular joint (TMJ) tomograms, com- puted tomography (CT) of the brain and face, magnetic reso- nance imaging (MRI) of the brain, complete blood count (CBC), Case presentation thyroid profile, and peripheral smear, all of which were within A 43-year-old woman presented to the Orofacial Pain Center normal limits. The CT scan showed a deviated nasal septum to with the chief complaint of pain in the mandible and mandibu- the left with bilateral inferior turbinate hypertrophy. The pan- lar teeth. oramic radiograph and full-mouth radiographs were negative Six months previously, following an episode of intense for dental pathology. yawning, the patient reported that she felt a “stretching sen- At the time of her presentation, the pain was severe (VAS sation” in her jaw and developed pain and sensitivity in the 80 mm). In the region of the mandibular anterior teeth, the mandibular anterior teeth. She consulted a general dental pain was sharp and continuous, with no known aggravating or practitioner and was prescribed multiple brands of desensi- relieving factors. The patient did not notice the pain during tizing toothpastes and medicaments, assuming her com- sleep. However, the patient reported disturbed sleep with diffi- plaints were related to dentinal hypersensitivity. At the time culty initiating and maintaining sleep. The patient had gastritis of onset of symptoms, the patient described the pain in the and a history of right sided Bell palsy a few months prior to the alveolar process of the mandibular anterior teeth as being onset of the symptoms of facial pain. She was prescribed pred- continuous, dull aching (20 mm on a visual analog scale nisolone and physiotherapy for the Bell palsy. Her medical and [VAS]) and the pain in the mandibular anterior teeth as similar family history was otherwise noncontributory. The patient’s job to a tooth being sensitive. was active and involved regular bending. The patient also Subsequently, she was referred to an endodontist who per- reported mouth breathing. Extraoral examination revealed a formed root canal treatments (RCTs) of the mandibular right moderately built and nourished, conscious, cooperative patient and left central and lateral incisors, presuming the complaints who was well-oriented with the surroundings. She had mild had an endodontic origin. She was prescribed multiple broad deficits on the right side of the face (weakness of the facial and narrow spectrum antibiotics, assuming an odontogenic muscles) due to Bell palsy. infection. The medications and RCTs failed to provide relief and TMJ and musculoskeletal evaluation revealed a range of the pain persisted. Hence, the RCTs were repeated and finally movement that was within normal limits. She had mild tender- the patient was advised to undergo extraction of the mandib- ness on the lateral and posterior pole of the right TMJ. Muscle ular right and left central and lateral incisors and both mandib- palpation revealed severe tenderness and trigger points in the ular canines 4 months after the pain complaints started. This right superficial masseter, sternocleidomastoid muscle (SCM), resulted in an aggravation and change in the quality of pain and anterior digastric muscle. Palpation of the trigger points in (from mild, continuous, dull aching pain to severe, continuous, the right anterior digastric reproduced the patient’s com- sharp pain [VAS 70 mm]). plaints. Intraoral examination revealed an edentulous area in The patient was then prescribed a trial of carbamazepine the region of the mandibular right and left central incisors, lat- 300 mg once daily, pregabalin 75 mg once daily, and vitamin eral incisors, and canines. A bony spicule was present in the B12, presuming the condition to be trigeminal neuralgia. The region of the extraction site of the mandibular right canines.

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GE

Subcutaneous tissue

Digastric Anterior Belly Digastric Anterior Belly 1

2

1 3 cm 2

Fig 1 The digastric muscle on ultrasound. Fig 2 Digastric trigger point injection.

On palpation of the bony spicule, the patient reported mild tion using a Luer-Lok syringe was slowly deposited in the anter- tenderness, but it did not reproduce the patient’s chief com- ior belly of the digastric muscle with a gentle needling motion plaint. A full-mouth radiograph taken 1 month previously was to break up the trigger point (Fig 2). The patient had complete negative for dental pathology. Topical local anesthetic spray relief of pain for 1 day (VAS 0 mm) and partial relief for 1 week was used and an infiltration of 1 mL of 2% lignocaine without (VAS reduced from 80 mm to 30 mm). She was followed up epinephrine local anesthetic injection bilaterally in the region with home care instructions on controlling predisposing, per- of the mandibular anterior teeth did not resolve the pain. The petuating, and precipitating factors, home care exercises, hard clinical examination, radiographs, and local anesthesia tests joint stabilization splint, amitriptyline 10 mg once daily for ruled out odontogenic sources of pain. A vapocoolant spray 1 month, physiotherapy, and postural re-education. She and stretch of the anterior digastric using ethyl chloride spray reported substantial relief of pain (VAS 10 mm).The patient was was performed and this relieved the pain of the chief complaint also referred for psychological counseling and was diagnosed completely. Spray and stretch of the anterior digastric muscle with comorbid depression, secondary to the facial pain. She using ethyl chloride spray reduced the pain significantly (VAS was treated with duloxetine 20 mg once a day. The pain relief 80 mm prior to the procedure, VAS 30 mm subsequently). The was sustained at a follow-up 16 months following treatment. source of pain was confirmed by palpation of the anterior digastric muscle and was relieved by vapocoolant spray and Discussion stretch. With the odontogenic causes ruled out, a diagnosis of myofascial pain due to referral from trigger point in the anterior Dental practitioners receive extensive training to diagnose and digastric was made. The patient was advised to undergo a trig- treat dental pathologies. Non-odontogenic toothache may ger point injection. occur due to referral of pain from structures in the head and The patient was then referred to a pain management phy- neck such as ear, nose, and throat (ENT) pathology, sinusitis, sician. The procedure was explained to the patient and TMD, neurovascular pain, and neuropathic pain.6 It often pres- informed consent was obtained. The area was isolated and ster- ents as a diagnostic enigma. Myofascial pain with referral from ilized with alcohol and povidone-iodine (Betadine). The digas- trigger points in the masticatory muscles can frequently refer tric muscle was determined using ultrasound (Fig 1). Following to intraoral structures7 and other distant structures.8 The pain in needle placement confirmation using the ultrasound, a 1-inch these instances can mimic odontogenic pain. Previously, cases long, 22-gauge needle was advanced into the anterior belly of of non-odontogenic toothache due to referral from trigger the digastric muscle. Following negative aspiration, the 1.8 mL points in the masseter and other masticatory muscles have of 2% lignocaine without epinephrine local anesthetic injec- been described.9-14

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3 Pain and sensitivity in the mandibular anterior teeth

Negative findings Clinical exam: • Percussion positive Dental cause • Percussion • Caries • Radiography • Bleeding on probing • Periodontal exam • Widened periodontal ligament • Periapical pathology

Diagnostic testing: • Local anesthesia (topical or injection)

No change in pain levels Pain reduction: • Non-odontogenic cause • Dental cause • Trigeminal neuralgia Positive: • Burning mouth syndrome Muscle palpation: • Myofascial pain • Pain reduced but not eliminated in • Muscles of mastication some continuous neuropathic pain • Cervical muscles Negative: conditions such as post-traumatic • Digastric • Neuropathic pain trigeminal neuropathy • Neurovascular pain

Fig 3 Flowchart for the diagnosis of non-odontogenic dental pain.

In the present case, the pain in the mandibular anterior in the masseter can refer to the mandibular molars, and anter- teeth and mandible was misdiagnosed as pain of odontogenic ior digastric trigger points can refer pain to the mandibular origin and irreversible procedures were performed. The institu- anterior region. tion of irreversible procedures resulted in progression of the The function of the anterior digastric muscle is to depress condition. The case highlights the importance of carefully col- and retrude the mandible. The action of the digastric muscle is lecting a patient history combined with a comprehensive clin- especially important at maximum opening and quick or forced ical examination. This facilitates the arrival at an accurate diag- jaw opening. The digastric muscle has a predominance of Type nosis of the source of pain, before initiation of an irreversible II muscle fibers, which enables quick opening; however, it has a procedure.10 Odontogenic pain may also co-exist with other very few muscle spindles and Type I muscle fibers. Thus it is orofacial pain conditions or headache disorders.15,16 In such unable to maintain prolonged tension.3 Trigger points in the instances, a local anesthetic injection block may be a useful digastric often develop in patients with parafunctional habits adjunct tool to differentiate odontogenic pain from non-odon- like bruxism, mouth breathing (it may be secondary to nasal togenic pain. The complete cessation of pain with local anes- obstructions such as a nasal polyp, or structural abnormalities thetic injection block generally indicates odontogenic origin. A in the nose such as a deviated nasal septum),3 and episodes of paradigm for the diagnosis of non-odontogenic toothache due intense yawning. Trigger points in the masseter and other ele- to myofascial trigger points is presented in Fig 3. vator muscles of the jaw may also result in trigger points in the Non-odontogenic pain may be referred from different mas- digastric muscle.3 Additionally, it has been suggested that key ticatory muscles and accessory muscles and masquerade as a trigger points in the SCM may also induce satellite trigger points toothache. The patterns of referral and method of palpation of in the anterior digastric muscle.3 As mentioned previously, the trigger points have been detailed in the Trigger Point Manual patient was a mouth breather, which could have predisposed by Simons et al.3 Trigger points in the anterior, middle, and pos- her to developing trigger points in the digastric muscle. terior temporalis may refer pain to the maxillary anterior region, A comprehensive evaluation of the masticatory muscles is premolars, and molars, respectively. Similarly, the trigger points essential. Reproduction of the patient’s pain complaint during

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Table 1 Differential diagnosis of odontogenic vs non-odontogenic pain from myofascial trigger points

Non-odontogenic pain from Odontogenic pain myofascial trigger points

Dental pathology such as caries, apical periodontitis Positive Negative Percussion of tooth Positive No change Palpation of trigger point No change Increase pain to referral site Response to spray and stretch No change Pain reduction Response to local anesthetic injection into trigger point No change Pain reduction Response to local anesthetic injection at tooth site Pain reduction No change

the clinical examination can help diagnose the source of pain. as cyclobenzaprine, carisoprodol, and amitriptyline.5,17 Amitrip- Table 1 describes the differentiating features between odonto- tyline and nortriptyline may be beneficial in chronic myofascial genic and non-odontogenic pain by myofascial trigger points. pain18 or patients with myofascial pain and concomitant sleep In the present case, the diagnosis was confirmed by reproduc- disturbances. Amitriptyline is a tricyclic antidepressant that is tion of the patient’s pain complaint by palpation of the anterior well validated in low doses for chronic pain. It is a serotonin-nor- digastric muscle, failure of local anesthetic injection blocks to epinephrine reuptake inhibitor,17 and is especially beneficial in relieve pain in the mandibular anterior teeth, negative findings chronic pain patients with sleep disturbances such as the pres- with intraoral radiographs and intraoral examination, and relief ent patient. Although the mechanism of action is still unclear, of pain through vapocoolant spray and stretch followed by trig- appliances such as a TMJ stabilization appliance have been ger point injections. The trigger point injections were accom- found to be beneficial in patients with TMD and are recom- plished using lignocaine without epinephrine. Epinephrine is mended in cases of painful TMD or TMD cases that present with generally avoided in trigger point injections as it may be myo- functional limitations. Patients with orofacial pain conditions toxic and constrict blood flow to the muscles. The treatment may have comorbidities such as depression, and in such was multidisciplinary. The case also reflects the importance of instances psychological counseling and psychiatric evaluation cross-referrals between physicians and dental practitioners to may be essential. Many cases of TMD may persist or recur, and aid in successful diagnosis and management of complex cases. in such cases physiotherapy may be recommended. Postural Predisposing, perpetuating, and precipitating events were re-education is also performed in patients with forward head identified, and addressed to prevent further recurrences. posture or poor work ergonomics. In the present patient, phar- Treatment of myofascial pain includes trigger point spray macotherapy and appliance therapy were done in the early and stretch, trigger point pressure release, trigger point injec- stages of treatment following trigger point spray and stretch tions, home care instructions, corrective actions, pharmaco- and trigger point injection. therapy, appliance therapy, psychological counseling, and General dental practitioners may encounter patients with addressing comorbidities such as depression, physiotherapy, complaints of pain in the teeth or alveolar process in the and postural re-education.5,17 The management paradigm for absence of dental pathologies on clinical and radiographic digastric trigger points is detailed in Fig 4. Trigger point spray examination. In these instances, an accurate history and com- and stretch, and trigger point pressure release is the first step. prehensive clinical examination may help in locating the source This aids in confirming the diagnosis and may be therapeutic in of pain. The site of pain is often different from the source of mild cases. If it provides relief or the relief is temporary, it may pain in myofascial pain with referral. In patients with myofascial be followed with a trigger point injection. Identification and pain with referral from trigger points in the anterior digastric treatment of predisposing, perpetuating, and precipitating muscle, the site of pain may be the alveolar process of the man- events is crucial for successful treatment and prevention of dible and the mandibular anterior teeth, whereas the source of recurrences. Patients are counselled on home care instructions, pain is the anterior digastric muscle. Hence, emphasis should corrective actions, and exercises to prevent recurrences. Phar- be on diagnosing and treating the source of pain rather than macotherapy of myofascial pain includes muscle relaxants such the site of pain.

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The key to successful treatment of toothache of non-dental origin lies in an accurate diagnosis. An accurate diagnosis Trigger point in the anterior digastric muscle stems from a logical process combining history, comprehen- sive clinical evaluation, use of appropriate diagnostic aids, and Trigger point spray and stretch and in certain instances, a trial of therapeutic agents. trigger point pressure release

Conclusion/recommendation Trigger point injection A case of myofascial pain with referral of the anterior digastric presenting as a non-odontogenic toothache in the mandibular Home care instructions, corrective actions anterior teeth was described. The management of the case with trigger point injections, pharmacotherapy, and physiotherapy was detailed. Trigger point injections to the anterior digastric Pharmacotherapy, appliance therapy muscle may be complicated to accomplish in a general dental clinic; however, the history and examination (including palpa- Psychological counseling and addressing comorbidities tion) are not. It is mandatory for general dental practitioners to such as depression institute appropriate referrals for further evaluation and man- agement when necessary, such as in cases where odontogenic Physiotherapy, postural re-education causes of toothache or facial pain may be a factor or when a 4 diagnosis is not apparent. Thoroughness in patient care is cru- cial and, as this case study illustrates, can result in avoidance of Fig 4 Flow chart depicting the management paradigm for digastric unnecessary, harmful, and/or irreversible procedures. trigger points.

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Mythili Kalladka Muralidhar Thondebhavi Consultant Pain physician, Apollo Specialty Hospital, Bangalore, India

Sowmya Ananthan Assistant Professor, Rutgers School of Den- tal Medicine, Department of Diagnostic Sciences, Newark, NJ, USA

Gautam Kalladka Assistant Professor, Department of Orthodon- tics and Dentofacial Orthopedics, Bangalore Institute of Dental Sciences, Bangalore, India

Mythili Kalladka Adjunct Assistant Professor, Orofacial Pain and Junad Khan Program Director, Orofacial Pain and Temporoman- Temporomandibular Disorders, Eastman Institute for Oral Health, dibular Disorders, Eastman Institute for Oral Health, University of Rochester, NY, USA Rochester, NY, USA

Correspondence: Dr Mythili Kalladka, Adjunct Assistant Professor, Orofacial Pain and Temporomandibular Disorders, Eastman Institute for Oral Health, 625 Elmwood Ave, Rochester, NY-14620, USA. Email: [email protected]

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