Some forms of chronic pain are thought to be driven and maintained by nociceptive input, which can drive plasticity within nociceptive pathways. We have previously identified abnormalities along the entire nociceptive pathway in chronic myalgic temporomandibular disorders (mTMD), including the trigeminal nerves, brainstem pathways, and in the thalamus and somatosensory cortex. These data suggest that there is a peripheral nociceptive drive in mTMD, but the source of this nociceptive activity remains unknown. Here, our aim was to determine whether structural abnormalities exist in the muscles of mastication of patients with chronic mTMD. Specifically, we tested whether the volume of the temporalis muscle and its tendon-aponeurosis complex (TAC, a structure that dissipates forces in a muscle) in mTMD patients differ compared to age- and sex-matched controls. To do so, we segmented these structures on T1-weighted structural magnetic resonance images. We found that muscle volumes in mTMD were not different to controls. However, the mTMD group had significantly smaller volumes of the bilateral temporalis TAC, and thus a smaller TAC-to-muscle volume ratio. These findings were consistent across 2 independent cohorts of 17 mTMD patients, compared to 17 age- and sex-matched controls. We propose a model where reduced TAC-to-muscle ratio could result in a predisposition to muscle tissue injury. In sum, abnormalities of the temporalis muscles in mTMD supports our hypothesis that chronic mTMD pathophysiology may be related to peripheral nociceptive barrage originating from the muscles of mastication.
Bibliographical noteFunding Information:
M. Moayedi was supported by the Bertha Rosenstadt Endowment Fund and held Canadian Institutes of Health Research (CIHR) Banting and Best Doctoral Research Award (2009-2012). K.D. Davis was supported by a CIHR Grant. P.-Y. (T.) He was supported by a CIHR summer studentship. The Centre for Advanced Dental Research and Care is supported by a donation from dentalcorp and Henry Schein Corporation (HCT). E.W.N. Lam was supported by a Dr Lloyd and Ms Kay Chapman Chair. L. Henderson holds an Australian National Health and Medical Research Council Grant (G182968). The Centre for Multimodal Somatosensory and Pain Research at the University of Toronto is funded by a grant from Canada Fund for Innovation and the Ontario Centres of Excellence (I.C. and M.M.). I. Cioffi was supported by the University of Toronto’s Faculty of Dentistry, and the University of Toronto Centre for the Study of Pain.
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- Masticatory muscles
- Myogenic TMD
- Temporalis muscle
- Temporomandibular disorders
ASJC Scopus subject areas
- Clinical Neurology
- Anesthesiology and Pain Medicine