Randomized Blinded Placebo-Controlled Clinical Trial of Caloric Vestibular Neurostimulation in Patients With Chronic TMD
Randomized Blinded Placebo-Controlled Clinical Trial of Caloric Vestibular Neurostimulation in Patients With Chronic TMD
The investigators propose to conduct a randomized blinded placebo-controlled clinical trial in patients with chronic TMD (N=20). Patients will be randomly assigned to receive either active treatment (caloric vestibular neurostimulation) or placebo. Data will be collected prior to and after treatment on thermal and mechanical pain thresholds, clinical signs and symptoms of TMD, and any adverse events.
Temporomandibular disorders (TMD) are musculoskeletal pain conditions characterized by pain in the temporomandibular joint and/or the masticatory muscles. TMD are amongst the most common chronic musculoskeletal conditions affecting 6 to 12% of the general population yet there are no medicines approved specifically for its treatment. TMD cause substantial suffering and TMD pain is the most common symptom that compels patients to seek therapy. One study found average ratings of pain intensity due to TMD of 4.3 on a 10-point scale, similar to the averages reported for chest pain and back pain. Studies consistently find that TMD has a pronounced impact on quality of life. Thus, a new successful approach to TMD therapy would have a significant clinical and economic impact.
Caloric vestibular stimulation (CVS) is a routine diagnostic test for the assessment of vestibular function and Central nervous system pathology. It is usually conducted by instilling cold or warm water into the external ear canal and has been shown to activate anterior cingulate, temporoparietal and insular cortices. In addition to its use as a diagnostic test, CVS has also been shown to reduce pain in several chronic conditions including migraine, phantom limb pain, spinal cord injury, thalamic pain, and complex regional pain syndrome.
Central sensitization is a common feature of the pain conditions shown to be alleviated by CVS. It is a dysfunctional state of the central nervous system in which pain is no longer coupled to a noxious peripheral stimulus. In the presence of central sensitization the response to a noxious stimulus is exaggerated and prolonged (hyperalgesia) and may involve areas outside the site of injury (secondary hyperalgesia). Pain can also arise spontaneously and can be elicited by innocuous stimuli (allodynia). While the neural mechanisms underlying the development of TMD are poorly understood, there is accumulating evidence that central sensitization plays a critical role in TMD pathogenesis. It has been proposed that there is a cyclical process in which TMD pain results in central sensitization that in turn predisposes patients to more pain. Thus any treatment that reverses central sensitization should in turn result in a decrease in pain.
Caloric vestibular stimulation (CVS) is a safe and effective procedure used for the diagnosis of brainstem injury and for balance assessment. As noted already, there have been intriguing observations in the literature suggesting that caloric vestibular stimulation can lead to the abatement of pain. When a caloric stimulation (warm or cool relative to body temperature) is applied to the ear canal, conduction (primarily via dense bone) to the inner ear, and in particular the prominence of the lateral semicircular canal (SCC), sets up convection currents in the endolymph. The resultant deformation of the cupula (membrane spanning the ampula of the SCC) leads to a phasic change in the tonic firing rate of hair cells at the base of the cupula, thereby altering the firing rate of the afferents of the vestibular nerve (thus a device delivering CVS may be viewed as a class of neurostimulator). The afferents map to nuclei in the brainstem (as well as some phylogenetically ancient, direct connections, e.g. to the thalamus and hippocampus) and then to the fastigial nuclei in the cerebellum. It is hypothesized that the method of action of CVS on pain relates to alteration of the phasic firing rate in the vestibular nerve afferents, which in turn alters the activation of the receiving areas (brainstem and cerebellum).
The primary impediment to therapeutic applications of CVS has been the lack of a clinical device that provides controlled, prolonged, and repeatable caloric stimulation. The use of "ice water" irrigation using syringes or even the water/air irrigators used in balance studies are not practical for treatment regimens that extend up to 10 minutes. Further, the applicants believe that a controlled, time-varying thermal waveform is essential to avoid the effects of adaptation of the cupula, which then attenuates control of the phasic firing rate of the hair cells.
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