Increased pain sensitivity of the upper extremities of TMD patients with myalgia to experimentally-evoked noxious stimulation: possibility of worsened endogenous opioid systems.

The purpose of this study was to examine whether or not temporomandibular disorder (TMD) patients with chronic masticatory myalgia have increased pain sensitivity at remote sites outside of the head and neck region, and to evaluate whether the endogenous pain inhibitory systems triggered ischemic pain functions favorably in those patients. Twenty female TMD patients with chronic myalgia and 20 controls participated in this study. Ischemic pain was produced to activate endogenous opioids. The pain threshold time, pain tolerance time, pain intensity and pain unpleasantness were compared between the TMD patients and controls. The pressure pain thresholds in the hand were also compared before, between, and immediately after the ischemic pain. The TMD patients showed higher severe pain intensity and unpleasantness values and had lower pressure pain thresholds in the hand. Although both groups showed an increase in the pressure pain threshold, there was less of an increase in the pressure pain threshold in the TMD patients than in the controls. These findings indicate that TMD patients have increased pain sensitivity at remote sites, and also indicate additional evidence that the endogenous opioid systems may become impaired in TMD patients with chronic masticatory myalgia.