| Objective: Myofascial pain syndrome is a common cause of chronic pain;this type of pain,caused by myofascial trigger points,has a high incidence in the general population.Myofascial trigger points can cause not only local pain,referred pain in distant areas,and limited joint mobility,but also anxiety,depression,and other complicationsin patients.As a non-fatal disease,myofascial trigger points without timely and effective treatment significantly reduce the patient's quality of life and may lead to loss of ability to work,which imposes a serious mental and economic burden on the patient's family and society.It is still unclear whether the myofascial trigger point is a peripheral or central sensitization.Treatments have been performed at the trigger points in clinical practice,but they did not achieve the desired long-lasting curative effect.Therefore,the status of treatment and the confusion being faced have prompted further questions.Is the chronic pain induced by myofascial trigger points a phenomenon of simple peripheral sensitization? Is the current treatment of myofascial trigger points effective? Is there a link between the central nervous system and the onset of myofascial trigger points? How do brain structure and function of patients with chronic myofascial pain change before and after treatment? Based on the above questions,patients with the most common trapezius trigger point pain were included in this study to assess the distribution range of intramuscular nerve terminal-dense areas in this muscle.Treatment was conducted by injecting drugs at the motor end-plates of the myofascial triggering points(intramuscular nerve terminal-dense areas),and the efficacy was examined.The changes in brain structure and function of patients with chronic myofascial pain before and after treatment were assessed using magnetic resonance imaging(MRI).Methods: 1)Twenty-two adult cadavers were collected,and the source and the shape of the extramuscular nerve of the trapezius were observed.The intramuscular nerve of the trapezius muscle was stained using modified Sihler's nerve staining technique to assess the distribution range of intramuscular nerve terminal-dense regions of the trapezius muscle and to localize them in the human body.One hundred twenty patients with chronic myofascial neck pain were enrolled and treated with injections of lidocaine in the intramuscular nerve terminal-dense area and trigger points,respectively,and the efficacies of the two treatment methods were examined.2)Thirty-seven patients with chronic pain induced by myofascial triggering points and 36 healthy volunteers were enrolled.Diffusion kurtosis imaging(DKI)was used to detect the gray matter microstructural differences between patients with chronic myofascial pain and healthy volunteers,and the possible correlation of the changes in the gray matter of patients with the disease duration,pain intensity,and age was analyzed.At the same time,presence of brain microstructural differences of the patients with myofascial pain before and after treatment was observed.3)The amplitude of low-frequency fluctuation(ALFF)in resting state functional magnetic resonance imaging(MRI)was used to explore the characteristics of local brain spontaneous nerve activity in patients with chronic myofascial pain in a resting state.Additionally,the correlation of the ALFF value for the brain regions with functional abnormalities with visual analog scale(VAS)score,disease course,and age in patients with chronic myofascial pain was analyzed.Based on the first and second parts,the changes in brain function of patients before and after treatment were further observed.Results: 1)The terminal nerve branch of the trapezius muscle had a "dendritic" distribution,and the terminal branches of each nerve were connected with each other in the middle of the muscle belly to form an S-shaped nerve-dense band.Compared with the injection group at myofascial trigger points,patients who received the lidocaine injection in the intramuscular nerve terminal-dense area for six months showed a significant decrease in the intensity and frequency of pain.In particular,increased efficacy was observed when the injections were administered at the intramuscular nerve terminal-dense area of both the middle-upper and lower parts of the trapezius muscle.However,the pain score also increased over time after the injection treatment at the intramuscular nerve terminal-dense area.2)Compared with the healthy control group,patients with chronic myofascial pain showed gray matter microstructural abnormalities that were mainly distributed in the brain regions involved in the limbic system and the pain matrix.The gray matter microstructural abnormalities of the right anterior cingulate gyrus and medial prefrontal cortex were significantly negatively correlated with the course of disease and pain intensity.After two months of treatment involving lidocaine injectionsin the intramuscular nerve terminal-dense area,the microstructural abnormalities at the anterior cingulate cortex and medial prefrontal cortex were still present,although patients' pain intensity had decreased significantly.3)Compared with healthy volunteers,patients with chronic myofascial pain had an increased ALFF value of the right thalamus,right hippocampus,right anterior cingulate gyrus,right anterior cingulate lobe,right posterior cingulate gyrus,and right superior frontal gyrus,and a decreased ALFF value ofthe right insular lobe.In addition,the average ALFF values of the right thalamus and anterior cingulate cortex were positively correlated with VAS score and pain duration.Compared with the values before treatment,the patients with chronic myofascial pain exhibited a significantly decreased VAS score after two months of treatment,but the ALFF values of the anterior cingulate cortex and the thalamus still increased.Conclusions: 1)The injection of lidocaine at the intramuscular nerve terminal-dense area for the treatment of myofascial pain was more effective than the injection of lidocaine at the trigger point,and significantly reduced the intensity and frequency of pain after six months of treatment.However,the pain intensity also increased over time.It was speculated that the dysfunction of the intramuscular nerve-dense area might be only one of the causes of the generation of myofascial trigger points.2)There were gray matter microstructural abnormalities in patients with chronic pain caused by myofascial trigger points,and the gray matter microstructural abnormalities in the right anterior cingulate cortex and medial prefrontal cortex were negatively correlated with the course of disease and pain intensity.Although the intensity and frequency of pain decreased significantly after two months of treatment,the microstructural abnormalities of the anterior cingulate cortex and medial prefrontal cortex still occurred,suggesting that the microstructural changes of the brain may play a role during the occurrence and development of myofascial triggering points.3)Abnormal brain functions occurred in patients with chronic myofascial pain,and the functional abnormalities in the brain regions did not improve after treatment.In conclusion,the results suggest that the pathophysiologic mechanism underlying myofascial trigger points may be a result of both peripheral and central effects.Patients with myofascial pain should receive timely and effective treatment to avoid transferring the noxious stimulation produced by myofascial trigger points into the central nerve system to the greatest extent.In the development of treatment strategies,one should not only strengthen the treatment of the peripheral nervous system,but also consider the protection of the central nervous system(brain tissues),to achieve a "cure" of brain structure and function. |
PDF Full Text Request