Clinical Evaluation of Botulinum Toxin a in the Management of Temporomandibular Myofascial Pain

Temporomandibular disorders (TMDs) are a group of musculoskeletal and joint issues that affect the temporomandibular joint (TMJ), masticatory muscles, and associated structures. Common patient presentations that can significantly affect quality of life include pain, joint sounds, limited mouth opening, headaches, earaches, and functional impairment (1,2). The multiple causes of TMD, which include parafunctional habits like bruxism, internal derangements, trauma, and myofascial dysfunction, make diagnosis and therapy challenging (3,4).

Physical therapy, occlusal splints, muscle relaxants, and nonsteroidal anti-inflammatory drugs (NSAIDs) remain the primary line of conservative treatment (4). However, some patients with myofascial pain do not react well to conventional therapeutic methods, necessitating other approaches (5). The neurotoxin botulinum toxin type A (BoNT-A) blocks the release of acetylcholine at the neuromuscular junction, resulting in muscle relaxation and temporary chemodenervation (6). Numerous clinical studies have demonstrated that BoNT-A improves jaw function, reduces the intensity of discomfort, and increases maximal interincisal distance in individuals with myofascial TMD (5-7). Even though there is noticeable pain relief, other trials show differing degrees of improvement in mouth opening, therefore the evidence is still inconclusive (6,7).

Given these disagreements, more randomized controlled trials (RCTs) are required to establish consistent treatment recommendations regarding dosage, injection sites, and follow-up schedules. The lack of local data from Pakistan about the use of BoNT-A in TMD therapy emphasizes the need for population-specific evidence.

Objectives:

To evaluate the effectiveness of botulinum toxin type A (BoNT-A) in patients with temporomandibular myofascial pain, by assessing changes in pain intensity and maximal interincisal distance compared with placebo.

• Botulinum Toxin Type A (BoNT-A) (Drug): Participants will receive a total dose of 100 units of Botulinum Toxin Type A (BoNT-A) administered by intramuscular injection into the bilateral masseter and temporalis muscles (25 U per side in each muscle). The injections will be performed using a 31G × 12 mm needle. Participants will be followed at 1 week, 1 month, and 3 months to assess pain intensity and maximal interincisal mouth opening.
• 0.9% Normal Saline (Placebo) (Drug): Participants will receive 0.9% normal saline by intramuscular injection into the bilateral masseter and temporalis muscles using the same injection technique, volume, and follow-up schedule as the experimental group. The placebo is used to maintain blinding and serve as the comparator.

Primary outcomes

• Pain Intensity Numerical Rating Scale [1 week, 1 month, and 3 months after injection.]: Changes in pain intensity can be measured using various scales, such as the 11-point Pain Intensity Numerical Rating Scale (PI-NRS), where 0=no pain and 10=worst possible pain. The PI-NRS is commonly used to assess pain intensity in chronic pain management. However, interpreting the clinical importance of changes from baseline on this scale can be challenging. Studies have estimated a clinically important difference on the PI-NRS by relating it to global assessments of change in multiple studies of chronic pain.
• Change in maximal interincisal mouth opening (MIO) [1 week, 1 month, and 3 months after injection.]: The maximum interincisal distance (MID) is a crucial measurement for assessing the function of the temporomandibular joint (TMJ) and the masticatory muscles. It is measured by the distance between the upper and lower incisors when the mouth is fully opened. This measurement is particularly important in evaluating TMJ disorders and can indicate the health of the jaw and its associated muscles.

Secondary outcomes

• Incidence of adverse events [hroughout the 3-month follow-up period.]: Incidence of adverse events
• Pain during mandibular movements [1 week, 1 month, and 3 months.]: Pain during mandibular movements

Sex: All, ages: 18 Years to 60 Years

Inclusion Criteria:

* History of TMD, no relief with conservative therapy after at least three months.
* Clinical diagnosis of bilateral arthrogenous disorder and myalgia.
* Moreover, TMD can be confirmed by diagnosis through MRI and CT examinations
* Pregnancy or lactation.
* Previous mandible or significant facial trauma.
* History of prior TMD treatment or cosmetic treatments of the face with BoNT/A.
* Any contraindication to BoNT/A as outlined in the XEOMIN package insert.

Exclusion Criteria:

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• Uzair Luqman, FCPS, Principal investigator, Riphah International University