Trigger Point Deactivation in MPDS: A Comprehensive Guide to Non-invasive Therapeutic Modalities

Introduction

Classification of temporomandibular disorders (TMD) was first introduced by Bell, which was later modified by Okeson.¹ Functional disorders of the masticatory system involving the temporomandibular joints (TMJs), the masticatory musculature, and the associated structures are included in temporomandibular disorders. Myofascial pain was first described as myofascial trigger points (MTrPs) pain in 1952 by Travell and Rinzler.² The pain is invoked from trigger points within myofascial structures. The MTrPs are various hyperirritable spots found within the skeletal muscle taut bands.³

Aetiology of myofascial pain and dysfunction is commonly considered to be from direct or indirect trauma, cumulative and repetitive exposure to strain, pathology of spine, physical inactivity and posture disturbances.^4,5 Correcting the underlying etiological cause is presently the widely accepted treatment strategy for Myofascial pain syndrome (MPS) therapy. Unless the prime cause is treated properly, reactivation of MTrPs may occur and myofascial pain may persist. Due to lack of any criteria specific for diagnosis of MPS, it becomes difficult to understand the underlying cause and pathology, the persistent trigger points and ultimately difficulty in providing definitive treatment.

This article aimed to explore the variety of treatment modalities for MPS. Nucleus of this article was to review various non-invasive therapies and pharmacological management of MPS with the purpose of providing the clinician with a wide understanding of treatment options for MPS.

Etiology

Myofascial pain dysfunction syndrome (MPDS) occurs due to multifactorial causes which may include severe bruxism, malocclusion, clenching of jaw, increased sensitivity to pain and anxiety/ stress. Hyperactivity of TMJ muscles and muscular dysfunction due to malocclusion are responsible factors for the clinical manifestations of MPDS. According to the psychophysiologic theory, muscle spasm is a factor for myofascial pain dysfunction syndrome. More often, apart from emotional factors, mechanical factors can be prime causative factors in stimulating chronic oral habits, which ultimately leads to muscle fatigue.⁶ After long dental appointment or more often after the extraction of mandibular third molar, complaints such as pain are observed. Possible etiological mechanisms include abnormal depolarization of muscle fibers, an excessive release of acetylcholine (ACh), and deficiencies in acetylcholinesterase enzyme activity, among others.⁷ Desegrated hypothesis for trigger points in myofascial region was presented by Simons (Figure 1). It is a six link chain initiating with atypical acetylcholine release which leads to increase in muscle fiber tension, seen as the taut band located in a trigger point of myofascial region. Local hypoxia occurs due to constriction of blood flow in a taut band. Hypoxia leads to disruption in mitochondrial energy metabolism decreasing ATP production, thus resulting in tissue discomfort and activation of pain receptors. This causes pain and potentiates abnormal release of acetylcholine.⁸

Clinical Presentation

Clinical examination and history is the gold standard in the diagnosis of myofascial region pain. Signs and symptoms vary among patients. Careful examination of TMJ functions, TMJ disorders, musculoskeletal system, dental diseases such as malocclusion is required. Common signs of myofascial region pain are MTrP which may be of two types: Active MTrP and Latent MTrP. Active MTrP is present in a muscle taut band and gives rise to a lump on palpation, known as jump sign, whereas latent TrP is nodular. Pain originating from different Myofascial Trigger Points (MTrPs) in the facial region can be referred to areas including the maxillary and mandibular teeth, tongue, alveolar ridge, palate, frontal and temporal regions, temporomandibular joint (TMJ), pharynx, lateral surface of the mandible, ear, and occasionally even the occiput. Commonly observed symptoms include widespread pain in the head and neck area, referred pain, and morning stiffness in facial muscles. Patients often have a history of emotional stress and disrupted sleep.⁹

Joint pain and dysfunction is seen as intermittent pain localized to preauricular region, around TMJ, which exacerbates on jaw movements. Joint dysfunction produces characteristic clicking sound of the TMJ. TMD is seen more commonly in females.

Following complaints are commonly observed:¹⁰

• Pain: Pain is severe and increases during stress.

1. May be bilateral/ unilateral
2. Periauricular region pain radiating to head

• Muscle tenderness

• Clicking sound in the TMJ

• Limitation of jaw movements

• On opening, jaw deviation may be seen

• Association may be seen with neck pain, otalgia or shoulder pain

Four cardinal signs and negative characteristics for MPDS have been proposed by Laskin (Table 1).11

Discussion

Management

MPDS can be managed by surgical as well as non-surgical methods.

As mentioned above, our aim was to focus on the conservative non-invasive methods of management in order to provide clinician a complete understanding of the protocols to be followed for such patients.

Lifestyle modification¹¹

1. Rest: There is relation between muscle tension and rest. In order to avoid excitement of trigger points by unconscious jaw posture, clenching or grinding of jaw, patient should be educated and made aware of the importance of jaw rest. 
2. Diet modification: Decreasing occlusal loading forces by avoiding chewing of hard food substances helps to rest jaw and avoids triggering of myofascial pain.

Pharmacologic management

1. Analgesic drugs:^12,13 The most commonly used drugs for MPDS are Nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs have few side effects and are easily available over the counter. The mechanism of action of non-steroidal anti-inflammatory drugs in MPS is still not clearly understood but it is clear that the analgesic properties of NSAIDs relieves pain. The lidocaine patch is a local anaesthetic transdermal preparation. This patch alters the potential of nerves to conduct pain impulses. Topical lidocaine has a promising role as a therapy for MPS and is an alluring option as it is not an oral systemic drug. Depressing action of opioid analgesic on CNS relieves pain, while non-opioid analgesic decreases pain without depressing CNS.
2. Muscle relaxants:¹⁴ Commonly used muscle relaxants in MPS are tizanidine, carisoprodol, chlorzoxazone, methocarbamol meprobamate, and cyclobenzaprine. Studies have suggested that tizanidine should be considered as a first-line agent for the treatment of MPS.
3. Anticonvulsants:¹⁵ Pregabalin and Gabapentin have analgesic, anticonvulsant and anxiolyticlike activities. These drugs decrease the release of certain neurochemicals, including noradrenaline, glutamate, and substance P. 
4. Antidepressants:¹⁶ Tricyclic antidepressants (TCAs) are medications indicated for chronic pain, neuropathic pain and fibromyalgia. It is postulated that Tricyclic antidepressants work on central noradrenergic and serotonergic signals, affecting the central pain pathways to alleviate pain. Antidepressants are indicated in the therapy of fibromyalgia and nerve pain conditions resembling MPDS. Commonly used Tricyclic antidepressant are Sumatriptan and Duloxetine. 
5. Anti-inflammatory agents: Frequently used anti-inflammatory agents are salicylates (aspirin), ibuprofen, indomethacin, oxicam, fenamic acid and diclofenac sodium.

Other Methods

1. Trigger point injections:¹⁷ Injection into myofacial trigger points is an effective and common treatment option and the mode of action can be considered to be due to mechanical disruption by the action of needle and interruption in the dysfunctional activity of involved motor endplates. MTrP injections may engage dry short- or long-acting anesthetics, or steroids. More often saline or a local anesthetic like lidocaine is injected. Trigger point injections with steroids can also be considered. This procedure leads to less discomfort and the effects are comparable to dry needling.
2. Botulinum toxin: Type A botulinum toxin (BoNT-A) is a dominant neurotoxin. It prevents contraction of muscle. Use of BoNT-A in the management of muscle pain has been under study recently and shows promising results. The analgesic properties may be attributed to its action of decreasing the production of glutamate and substance P.¹⁸

Type B botulinum toxin (BoNT-B) has its action by cleaving synaptobravin, which is a part of VAMP (Vesicular associated membrane protien). Cleaving these protein causes muscle weakness as release of acetylcholine (Ach) at neuromuscular junction gets blocked.

Non Pharmacological Methods

1. Dry needling:^19,20 Dry needling procedure necessitate a thin needle to be inserted through the skin in order to stimulate myofascial trigger points. Dry needling is contemplated as one of the rapid methods to inactivate myofascial trigger points. Needle is inserted directly into the MTrPs and is moved around with in and out technique, and also in multiple directions. It is one of the most efficacious ways to inactivate a trigger point and alleviate pain.
2. Manual therapy/ Massage therapy:²¹ Manual therapy/ Massage therapy is a routinely used treatment for MPDS as it has been regarded as one of the most effectual techniques for the MTrPs inactivation. It includes, stretch therapy with spray (where a taut band is stretched immediately after cold spray), deep-pressure massage, myofascial release and superficial heat. Blood flow increases due to massage therapy and it leads to warming up of muscles which ultimately decreases muscle stiffness and reduces pain. During massage, thumb pressure on trigger points initially will aggravate pain and then release muscle tension.
3. Ultrasound therapy:²² Ultrasound is a therapeutic method employed for addressing myofascial pain, as it transforms electrical energy into sound waves to deliver heat energy to the muscles. Ultrasound machines act by transmitting the sound waves into the tissues through a sound-conducting gel which is applied to the skin. These sound waves heat up causing muscles relaxation, improves flow of blood to muscle, and removes the scar tissue. The action of ultrasound as a pain reducer is moderate, but it reduces the muscle stiffness and when done before stretching, increases the mobility. 
4. TENS:²³ Transcutaneous electric nerve stimulation (TENS) is a treatment method that utilizes electrical current. The electric current stimulates nerve fibers to provide relief from pain. TENS is under study since 1970s and has recently been assessed for the treatment of MPDS. TENS cannot be used as a monotherapy, instead should be used as an axillary therapy to help relieve MPS.
5. Magnetic stimulation:²⁴ Magnetic stimulation (MS) is a latest treatment option that is being inspected for MPDS. However, only few studies exist and the exact therapeutic mechanism of action of magnetic stimulation for MPS remains uncertain. More confirmation is required to consider magnetic stimulation as an effective treatment modality.
6. Laser therapy:²⁵ Laser therapy has a long history in the treatment of MPS. When the laser light source is applied to the skin, photons penetrate several centimeters into the skin and are absorbed by the mitochondria, the energy-producing part of cells. This process promotes tissue repair and accelerates healing. Laser therapy reduces muscle spasm and arterioles, providing analgesic effects. This results in improved tissue oxygenation, ultimately increasing the metabolic rate of tissues. As a result, laser therapy can disrupt the cycle of trigger points
7. Occlusal splint therapy:²⁶ Aim of occlusal splint therapy is to establish harmony of neuromusculature in the masticatory system. With the help of removable appliances, occlusal splints create a mechanical drawback for parafunctional forces. Relaxation of masticatory muscles, protection of the teeth and jaws from the effects of bruxism can be achieved by occlusal splint. With the help of occlusal splints, the condyles and jaws can be repositioned into centric relation. Small occlusal interferences change muscle activity coordination. Occlusal splints cause relaxation of muscles and decrease the stress on the joint. Various splints used in occlusal splint therapy include non-permissive, permissive, soft rubber (silicone) and hydrostatic splints.

Conclusion

Living with MPS can be quite challenging. It is crucial to identify the factors that trigger the activation of trigger points in myofascial pain, as this understanding is vital for effective treatment. Treating MPDS should primarily focus on comprehending and addressing the root causes of the symptoms and deactivating trigger points. Managing MPS effectively requires a holistic approach, which includes making lifestyle modifications and utilizing both pharmacological and non-pharmacological interventions. There is no single treatment that can be deemed as the best, but by employing the aforementioned methods, it is possible to successfully manage the pain and other symptoms associated with MPS. Among the treatment modalities examined, trigger point injections and dry needling stand out as essential interventional options. NSAIDs are useful for pain relief and stress reduction. Emerging therapies such as laser therapy and ultrasound hold promise for the future. Further research is needed to establish evidence-based treatment options and algorithms for MPDS.

Conflict of Interest

None