Evaluation of the Sympathetic Skin Response to the Dry Needling Treatment in Female Myofascial Pain Syndrome Patients

This prospective controlled study investigated the effects of dry needling on sympathetic nervous system activity in women with myofascial pain syndrome (MPS), using the sympathetic skin response (SSR) as an evaluation measure. Myofascial pain syndrome is a complex condition involving both sensorimotor and autonomic components, characterized by the presence of myofascial trigger points in approximately 30% of affected individuals. The study was conducted at the Department of Physical Medicine and Rehabilitation of the University of Istanbul, between June and September 2011, with approval from the institutional ethics committee. It included 29 women with pain in the trapezius muscle for more than 3 months and 31 healthy controls, all between 18 and 40 years of age with regular menstrual cycles.

The exclusion criteria were strict, eliminating conditions that could affect the sympathetic skin response, such as diabetes, rheumatoid arthritis, central or peripheral nervous system diseases, use of antidepressants or anxiolytics, and history of sympathectomy. The treatment protocol consisted of three weekly dry needling sessions, each lasting 20 minutes. During each session, a maximum of six needles (three on each side) were used, applied directly to the trigger points of the trapezius muscle after sterilization with alcohol. The needles, sized 0.25 × 40 mm or 0.25 × 25 mm depending on skin thickness, were manipulated at 10 minutes to recreate the stimulus.

Outcome measures included sympathetic skin response, pain intensity by visual analog scale (VAS), and pressure pain threshold measured with an algometer. The SSR was assessed using electromyography equipment with surface electrodes, applying electrical stimuli to the median nerve at the wrist. Assessments were performed in a quiet, dark environment with the temperature controlled at 25 °C, with patients in the supine position and eyes closed. The results demonstrated significant efficacy of dry needling in the treatment of MPS.

Pain intensity, measured by the VAS, decreased significantly from 6.82 ± 1.46 to 3.58 ± 2.62 in the fourth week post-treatment (P < 0.001). The pressure pain threshold also improved significantly on the right side, increasing from 4.32 ± 1.35 kg/cm² to 4.67 ± 1.19 kg/cm² (P < 0.05). The number of trigger points decreased from 5.17 ± 1.19 to 4.38 ± 1.86 (P < 0.01). As for the sympathetic skin response, a significant reduction in amplitudes and an increase in latencies were observed bilaterally in the patient group after treatment (P < 0.001), while the control group showed no significant changes.

The clinical implications of this study are important, as it provides objective evidence that dry needling not only reduces pain and improves pain threshold but also modulates sympathetic nervous system activity in patients with MPS. This is the first research to systematically evaluate the neurophysiological effects of dry needling using the SSR, suggesting that sympathetic hyperactivity plays an important role in the pathophysiology of the condition. The findings support the theory that myofascial trigger points involve changes in the central and autonomic nervous systems and are not merely a local muscular phenomenon. The treatment proved to be safe, with no adverse events reported during the three sessions or in the follow-up period.

Limitations include the relatively small sample size, the inability to blind due to the nature of the procedure, the SSR measurements being performed by the same clinician who applied the treatment, and possible habituation in the repeated SSR measurements. In addition, questions about autonomic symptoms such as sweating, skin temperature changes, or piloerection were not included in the questionnaire, which could have provided complementary data. The study did not standardize differences across menstrual cycles, which could influence the results. Despite these limitations, the study represents an important advance in understanding the neurophysiological mechanisms of dry needling and provides a scientific basis for its clinical use in myofascial pain syndrome, highlighting the need for future studies with larger samples and longer follow-up periods.