Long-term orofacial pain reduction after repeated botulinum toxin injection into masseter muscles

Abstract

<h3>Objectives</h3> Neurotoxin injection into muscles to reduce movement or pain has seen increasing use and study. For orofacial pain, however, patient selection factors and long-term efficacy are not well characterized. The objective of the present study was to describe the clinical characteristics and effects in a series of patients with temporomandibular disorder [TMD] pain who had received multiple masseter neurotoxin injections over the course of years. <h3>Methods</h3> Patients referred for tertiary/quaternary care within the oral medicine clinical services from April 2015 to December 2019 were investigated. At least 40 patients with TMD pain were treated with botulinum toxin over this time period. Extensive baseline questionnaires along with pain drawings were used to characterize the patients, including graded chronic pain and related Pain, Enjoyment of Life and General Activity [PEG] scales. Symptom Checklist 90 Revised [SCL-90 R], General Anxiety Disorder 7-item [GAD-7], and Patient Health Questionnaire 9 [PHQ-9] psychological measures were also administered. Diagnostic Criteria for Temporomandibular Disorders [DC-TMD] examinations were done at each visit, along with standardized assessments of neurosensory abnormalities, with masseter and temporalis estimated volume. Fifty units of incobotulinum toxin A were injected into superior and inferior masseters bilaterally in each patient. Returning patients were seen in follow-up from 1 to 4.5 years later in the clinic with extensive metrics. <h3>Results</h3> Of 40 patients with TMD treated with at least 1 encounter with neurotoxin, 4 were located who had received at least 3 injection procedures over 12 months or longer and reported 50% or greater reduction in average pain intensity and pain impact. These patients' ages were 27, 29, 29, and 32 years; 3 were female. All reported having TMD pain for more than 5 years, and all were diagnosed with masseter myalgia, masseteric hypertrophy, definite sleep bruxism, migraine or tension-type headache, and mild to moderate psychological distress. All 4 were treated initially with self-care, nonsteroidal anti-inflammatory drugs, muscle relaxants, and occlusal appliances with some success, but they desired more reduction of pain and pain impact. All patients reported pain reduction after neurotoxin within 2-3 weeks, with effective (50-100%) pain relief for up to 6 months. Total injection visits ranged from 3 to 9 over the course of 1 to 4.5 years. <h3>Conclusions</h3> For a subset of patients with subacute TMD masseter pain, botulinum toxin injections resulted in substantial reductions in orofacial pain intensity and impact that could be sustained with repeated injections.