• Andreas Dawson, Niclas Stensson, Bijar Ghafouri, Björn Gerdle, Thomas List, Peter Svensson, and Malin Ernberg.
• Center for Oral Rehabilitation, Östergötland County Council, Linköping, Sweden. andreas.dawson@regionostergotland.se.
• J Headache Pain. 2016 Dec 1; 17 (1): 65.

BackgroundDopaminergic pathways could be involved in the pathophysiology of myofascial temporomandibular disorders (M-TMD). This study investigated plasma levels of dopamine and serotonin (5-HT) in patients with M-TMD and in healthy subjects.MethodsFifteen patients with M-TMD and 15 age- and sex-matched healthy subjects participated. The patients had received an M-TMD diagnosis according to the Research Diagnostic Criteria for TMD. Perceived mental stress, pain intensity (0-100-mm visual analogue scale), and pressure pain thresholds (PPT, kPa) over the masseter muscles were assessed; a venous blood sample was taken.ResultsDopamine in plasma differed significantly between patients with M-TMD (4.98 ± 2.55 nM) and healthy controls (2.73 ± 1.24 nM; P < 0.01). No significant difference in plasma 5-HT was observed between the groups (P = 0.75). Patients reported significantly higher pain intensities (P < 0.001) and had lower PPTs (P < 0.01) compared with the healthy controls. Importantly, dopamine in plasma correlated significantly with present pain intensity (r = 0.53, n = 14, P < 0.05) and perceived mental stress (r = 0.34, n = 28, P < 0.05).ConclusionsThe results suggest that peripheral dopamine might be involved in modulating peripheral pain. This finding, in addition to reports in other studies, suggests that dopaminergic pathways could be implicated in the pathophysiology of M-TMD but also in other chronic pain conditions. More research is warranted to elucidate the role of peripheral dopamine in the pathophysiology of chronic pain.

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