The Effect of Botulinum Toxin A (BOTOX®) on Headache Attributed to TMD - An Open Label Trial

Temporomandibular Disorders (TMD) is a collective term, embracing a number of clinical problems that involve the masticatory muscles, the temporomandibular joint (TMJ) and the associated structures. The prime manifestation consists of pain of a persistent, recurring, or chronic nature . Pain-related TMD can affect the individual's daily activities, psychosocial functioning, and quality of life . The prevalence of TMD is about 10 % in the general population, making it the second most common musculoskeletal condition, after chronic lower back pain, that results in pain and disability . It has been estimated that the annual TMD management cost in the USA, excluding diagnostic imaging, in the last decade was approximately $4 billion.

The pathophysiology of pain-related TMD is poorly understood. However, multiple risk factors have been identified, such as, gender, pain during jaw function and palpation, oral parafunctions, other pain conditions, pain sensitivity and psychosocial characteristics. Because of its multifactorial nature, a multimodal conservative treatment approach is recommended, including patient education, behavioral management, physical therapy, pharmacotherapy, and occlusal splints.

Among the pain-related TMD conditions are "Headaches Attributed to TMD". This diagnosis has replaced "Headaches or facial pain attributed to Temporomandibular Joint (TMJ) disorder" described in the International Classification of Headache Disorders II (ICHD-2). It is characterized by pain in the temple area secondary to pain-related TMD that is modified by function and parafunction affected by jaw movement, function, or parafunction.

In general, headache treatment is either abortive or prophylactic. Abortive treatment manages acute headache and prophylactic treatment aims to reduce the frequency and severity of the attacks. Intramuscular injections with Botulinum Toxin (BTX) are used in the prophylactic treatment of migraine and tension type headaches. The mechanisms by which the analgesic effects of BTX are mediated are not fully understood. One mechanism is the inhibition of neurogenic inflammation by blocking neurotransmitter release from sensitized nociceptors, thus reducing peripheral sensitization. In vitro, BTX has been found to inhibit Calcitonin Gene-Related Peptide (CGRP), and BTX reduces the vascular response to algogenic substances such as capsaicin applied to human skin. Other potential analgesic mechanisms include retrograde transport of BTX by sensory neurons and inhibition of neurotransmitter release by their central terminals.

In recent years, BTX has also been used in the treatment of myogenous-TMD with mixed results. Two randomized controlled trials (RCTs) showed therapeutic benefits of BTX in the management of myogenous -TMD, while another 3 RCTs reported no significant effect of BTX in chronic myogenous -TMD pain. Varying patient samples, methodologies, and sample sizes may explain the differences. Additionally, the results have been compromised by poor methodologies, such as insufficiently powered clinical trials, and open-labeled studies. More recently, a systematic review of randomized controlled trials concluded that no consensus could be reached on the therapeutic benefit of BTX on TMD. More so, no trial on the effectiveness of BTX on the prophylactic treatment of headaches attributed to TMD has been reported to date.