Myofascial orofacial pain (MOP) is caused by damage to the masticatory muscles. It is the leading one in the overall structure of all prosopalgias. Neuropathic signs are found in the clinical picture of the disease, which leads to overdiagnosis of trigeminal neuropathy. The search for mechanism-based therapy that will ensure adequate pain control is an urgent task. To this end, it is necessary to study in more detail the pathogenetic mechanisms of pain in MOP.

The purpose of the study. To determine the main mechanisms of the formation of chronic pain in myofascial orofacial pain; to clarify the possibilities of botulinum therapy, taking into account the known facts about the analgesic effect and the effect on neuroplasticity of botulinum toxin type A.

MATERIALS AND METHODS

A prospective study was conducted in which 205 patients (123 women, 82 men) with MOP aged 35 to 51 years participated. Clinical neurological studies and neuropathic pain screening were conducted using the DN4 and painDETECT questionnaires. Emotional disorders (depression and anxiety) were studied using the Beck and Spielberger questionnaires. Thirty patients with MOP underwent botulinum therapy of the masticatory muscles using botulinum toxin type A (Relatox) for muscle relaxant and analgesic purposes, as well as studies of the effect of botulinum toxin on the mechanisms of central sensitization.

RESULTS

All patients with MOP had aching, pressing, and bursting pains in the parotid-masticatory region. Bimanual palpation of the masticatory muscles revealed myofascial trigger points, the irritation of which caused increased pain. In a clinical study of patients with MOP, spontaneous and evoked sensory phenomena were identified. Spontaneous disorders in the form of numbness, tingling, cold, and burning were reported in 24.3% (n=50) of cases. The induced sensory disorders in the form of cutaneous allodynia were determined on the side of pain localization in the parotid-masticatory region, as well as in another region — on the skin of the upper auricle and temporal region (29.2%, n=60), which corresponds to the innervation zone of the auritotemporal nerve (V3). The phenomena of secondary hyperalgesia (18%, n=37) were detected in the extratrigeminal, namely in the cervical-occipital region on the pain side. When examining the sensitivity to a needle prick in this area, increased pain in the face was determined. An analysis of the data obtained from the DN4 and painDETECT questionnaires in patients with MOP revealed neuropathic descriptors: a feeling of numbness — 35%, tingling — 22%, burning — 19%, chilliness (feeling cold) — 15%, the presence of cutaneous allodynia (pain on a non-painful stimulus) was noted by 23% of patients. As a result of the test study, the patients were divided into two groups: group 1 — with the presence of neuropathic pain according to the DN4 questionnaire (DN4 ≥4 points); group 2 — without neuropathic pain according to the DN4 questionnaire (DN4<4 points). Patients in group 1 were characterized by higher pain intensity on the visual-analog scale (VAS): 6.9±0.98 points versus 5.5±0.82 points (p=0.14). When comparing the results of the assessment of reactive anxiety (RA) and personal anxiety (PA), significantly high values were revealed in patients with neuropathic pain (DN4 ≥4): RA 50.4±1.7 points versus 40.2±2.5 points (p<0.05); PA 50.8±3.5 points versus 31.7±2.1 points (p<0.05). The level of depression in group 1 patients was also significantly higher than in group 2 patients: 25.2±1.8 points versus 15.3±3.1 points (p<0.05). Emotional disorders in the form of high levels of anxiety and depression determine the special behavior of the patient, lead to a significant limitation of coping strategies. The dynamics of clinical manifestations and testing in 30 patients who received local injections of botulinum toxin type A (Relatox) into the masticatory muscles was as follows. 1 month after the procedure, there was a significant decrease in VAS pain intensity in both groups of patients (6.2 points at the beginning versus 4.8 points after 1 month in the 1st group, p<0.01). Sensory phenomena also underwent positive changes. The dynamics of the representation of spontaneous sensory disorders showed the following: 33% at the start of therapy versus 9.5% after 1 month (p<0.01); the representation of induced sensory disorders: 23.8% at the beginning versus 4.7% after 1 month (p<0.01); secondary hyperalgesia: 12.5% at the start versus 3.5% after 1 month (p<0.01). The data obtained from anxiety and depression questionnaires showed good dynamics: RA/PA 49.6±1.2/47.3±1.8 points versus 25.4±2.1/23.8±2.3 points after 1 month (p<0.01); depression 23.9±1.3 points versus 18.2±2.2 points after 1 month (p<0.01). The results of the dynamics of psychological questionnaires correlate with good dynamics on the pain catastrophization scale (18.2±2.9 points at the start of therapy versus 14.4±3.3 points after 1 month, p<0.01).

CONCLUSION

The data obtained showed the involvement of two mechanisms in the pathogenesis of chronic myofascial orofacial pain: nociceptive and dysfunctional. In 35% of cases, central sensitization plays a leading role and determines the presence of dysfunctional pain in the structure of chronic myofascial pain. In this regard, the protocol for the treatment of chronic myofascial orofacial pain should include an effect on all pathogenesis factors. Local injections of botulinum toxin type A are a universal method of influencing the mechanisms of peripheral and central sensitization due to the selective muscle relaxant, analgesic effect. The effect of botulinum therapy on sensory symptoms may be related to the decompression of neurovascular structures, which presumably occurs during muscle relaxation of the masticatory and temporal muscles proper, as well as the effect on neuroplasticity processes in the central nervous system.