Dry Needling for Myofascial Pain: Prognostic Factors

Myofascial pain syndrome (MPS) is a common cause of musculoskeletal pain that results from the activity of myofascial trigger points (MTrPs). This condition is characterized by referred pain, motor dysfunction, and autonomic phenomena. Dry needling, a technique that involves inserting needles into trigger points without injecting substances, has been proposed as an effective alternative to conventional treatments. This prospective cohort study was conducted to evaluate the outcomes of dry needling in patients with MPS and to identify predictive factors for symptom persistence.

The study included 92 patients with chronic myofascial pain of at least 3 months' duration, treated at the pain clinic of Pingtung Christian Hospital in Taiwan, between February and October 2008. Inclusion criteria included nonspecific musculoskeletal pain, the presence of tender points in palpable taut bands, the ability to distinguish different pain intensities, a referred pain pattern, and a local twitch response. The treatment protocol consisted of dry needling of the trigger points using sterile 32G acupuncture needles 80 mm in length. After skin penetration, the needle was inserted into the taut band to elicit a twitch response.

The needle was then partially withdrawn and reinserted repeatedly until no further twitches were observed. After inactivation of the trigger points, the specialist performed passive stretching of the involved muscle to its normal length. The patients then performed muscle-stretching exercises. All participants received eight needling protocols administered over an 8-week period.

Outcome assessment was performed using the Taiwanese version of the Brief Pain Inventory (BPI-T), which measures pain intensity and its interference with daily life on a 0-10 numerical scale. Data were collected at baseline and after 2, 4, and 8 weeks. Statistical analysis used generalized estimating equations (GEE) to determine mean improvements in scores and to identify effective predictors of change. The results showed that the dry needling protocol significantly reduced both pain intensity and its interference with daily life.

Pain intensity—including worst pain, average pain, and current pain—showed a significant reduction at the 2-week point (p < 0.001). Worst pain and average pain had a large effect size (-0.67 and -0.68, respectively) at the 2-week point. At week 8, the reduction slopes for aggregate pain interference differed significantly from those observed at the 2-week point (p < 0.001). The analysis of predictive factors revealed that long duration of pain symptoms, high pain intensity, poor sleep quality, and repetitive stress were associated with unfavorable outcomes.

Specifically, pain duration was significantly and positively related to worst pain and aggregate pain interference. Sleep deprivation was significantly and positively related to worst pain and average pain. Repetitive work was significantly and positively related to current pain. These findings suggest that, although dry needling is effective in reducing pain and its interference, certain demographic factors and disease characteristics may influence treatment outcomes.

The proposed mechanisms for the efficacy of dry needling include mechanical disruption of muscle fibers and increased local blood flow, which are important factors in pain relief. The technique of passively stretching muscles to their normal length can inactivate trigger points, reduce referred pain, and improve range of motion. Limitations of the study include an inadequate sample size to demonstrate improvement in all measurements, the absence of a control group, and the failure to consider psychological factors such as dysfunctional pain cognition. Despite these limitations, the results suggest that dry needling combined with muscle-stretching techniques has great potential to improve the quality of pain management in patients with MPS.