Pain responses to experimental chewing in myofascial pain patients

Although patients with myofascial pain of the masticatory muscles often report that chewing exacerbates their pain, this has never been verified experimentally. In this study, pain was assessed before and after chewing in 20 asymptomatic subjects and in 61 patients with muscle pain. First, self-reports of pain were obtained with a checklist and on five-point category scales (CAT) at the screening visit. None of the asymptomatic subjects reported that mastication or other jaw movements caused pain. On the other hand, the majority of patients reported that movements were painful (67.2%, checklist; 78.7%, CAT). Afterward, pain intensity at rest and after chewing on wax for 3 min was reported on 100-mm Visual Analogue Scales (VAS). No asymptomatic subjects had pain before or after the chewing test, while about 50% of the patients reported an increase of pain after chewing. In this subgroup, mean pain intensity increased by 102.6%. However, mean pain intensity after chewing decreased by 56.6% in about 30% of the patient sample. These patients had significantly higher resting pain than the first subgroup. These data show that a short chewing test can exacerbate pain in most myofascial pain patients but has no effect in asymptomatic subjects. Surprisingly, the exercise decreased pain in an important subgroup of patients. These results suggest that two subgroups of myofascial pain patients may exist with opposite reactions to exercise. It remains to be seen if these reactions are due to two different pathologies or to the fact that the pre-exercise pain levels were significantly different in the two groups.