Chronic pain involves complex processes of genesis and neural conduction due to activation of peripheral and central mechanisms of pain maintenance. Many chronic patients are refractory to different types of treatment, which leads to the suspicion that somehow they are not fully effective and probably some mechanism of pain generation and/or maintenance is still unknown. Based on that, the aim of the present study is to evaluate the mechanisms of conduction, maintenance and pain modulation in patients with different types of chronic pain conditions. Ninety two women were evaluated, divided into 5 groups: Group I, 20 patients with Myofascial Pain of the masticatory muscles; Group II, 20 patients with Fibromyalgia; Group III, 20 patients with Chronic Daily Headache; Group IV, 12 patients with Trigeminal Neuralgia and Group V, 20 healthy asymptomatic patients. Two questionnaires were used, the STAI and the OHIP-30, to measure state anxiety and quality of life related to painful condition diagnosed, respectively. All patients underwent Quantitative Sensory Tests such as: Pressure Pain Threshold, Mechanical Detection Threshold, Mechanical Pain Threshold, Ischemic Pain Tolerance, Cold Pain Sensitivity, After- Sensation and Control Pain Modulation. An Electrodiagnostic Test, the Current Perception Threshold, using the apparatus Neurometer CPT/C (Neurotron®) was also performed. Three different regions were evaluated for each patient, for each test: trigeminal, cervical and extratrigeminal. Data were gathered and subjected to statistical analysis (ANOVA, Tukey, t-Student), adopting a significance level of 5% for all tests. All patients had high levels of anxiety and greater impairment of their quality of life, when compared to controls. Groups I, II and III showed significantly lower values of Pressure Pain Threshold than Group V. Group III had a significantly higher Mechanical Detection Threshold than Group V. Groups I, II, III and IV showed statistically lower values for Mechanical Pain Threshold and Ischemic Pain Tolerance than Group V. The ability to activate the mechanism of endogenous modulation, evaluated with the Controled Pain Modulation test, is impaired in women with Fibromyalgia and Myofascial Pain. There was no significant differences in the Current Perception Threshold (CPT) between Groups I, II, III and V. Group IVshowed a CPT to 5 Hz frequency significantly lower than Group V for the trigeminal region, indicating an hyperesthesic condition due to inflammation of the trigeminal nerve, characterizing neuropathic pain. According to the results, Groups I, II and III seem to share a common pain mechanism and similar etiology, with no significant damage to neural structures but a change in the processing and modulation of nociceptive stimuli, characterizing a dysfunctional pain. The results of this study showed evidence of the presence of central sensitization process and impaired endogenous modulation system in patients with Myofascial Pain, Fibromyalgia and Chronic Daily Headache.
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