Acupuncture analgesia: Areas of consensus and controversy

This comprehensive review examines 40 years of acupuncture research, focusing especially on pain treatment. The author, one of the pioneers in the scientific study of acupuncture, analyzes both areas of consensus and controversies in the scientific literature. The bibliometric analysis reveals dramatic growth in acupuncture publications after 1998, with more than 40% of studies focused on pain and analgesia. Of the more than 40 conditions endorsed by the World Health Organization for acupuncture treatment, pain stands out as particularly responsive.

The study clarifies fundamental concepts about acupuncture's mechanisms of action. Robust evidence demonstrates the involvement of the nervous system, contradicting the traditional theory of meridians as energy channels. Studies in healthy humans in the 1960s showed that the analgesic effect of manual acupuncture at LI-4 (Hegu) was abolished by deep local anesthesia but not by superficial anesthesia, confirming the importance of nerve innervation in deeper structures.

A fundamental finding was the differentiation between low-frequency (2 Hz) and high-frequency (100 Hz) electroacupuncture. These modalities activate different families of endogenous opioid peptides: 2 Hz favors the release of enkephalins and endorphins, while 100 Hz preferentially stimulates dynorphins. This difference is not only quantitative but qualitative, as there is no cross-tolerance between the two frequencies. The dense-disperse mode, alternating 2 Hz and 100 Hz every 3 seconds, produces a synergistic effect.

For acute pain, especially postoperative pain, the evidence is consistently positive. Systematic reviews show a significant reduction in opioid consumption and decreased pain intensity when acupuncture or electroacupuncture are used in the perioperative period. The effect is most pronounced when applied both pre- and postoperatively.

In chronic pain conditions, results are more variable. For chronic low back pain, studies show benefits compared with untreated controls, but they do not always significantly outperform placebo controls. Shoulder pain shows a more consistent response, with 65% of patients showing a 50% reduction in pain compared with 24% with sham acupuncture. For osteoarthritis, results depend on factors such as the number of sessions and the use of electrical stimulation.

The question of placebo control in acupuncture studies represents a significant methodological challenge. Different strategies include blunt needles that do not penetrate the skin, non-acupuncture points, and minimal electrical stimulation. Functional neuroimaging studies suggest that, although real and sham acupuncture may produce similar pain relief, the brain mechanisms are distinct.

The study establishes principles for parameter optimization: an optimal duration of 30 minutes per session, multiple sessions for chronic pain, and intensity adapted to the patient's condition. In inflammatory conditions, lower intensities are more effective. Point specificity remains controversial, although neurobiological studies suggest functional differences between stimulation sites.

The clinical implications are clear: acupuncture and related techniques constitute a valid, safe, and cost-effective therapeutic option for pain management. The scientific evidence supports specific physiological mechanisms beyond the placebo effect, especially when parameters are optimized according to current evidence.