Acupuncture mechanisms for clinically relevant long-term effects – reconsideration and a hypothesis

From clinical research, in which the author has been involved, the conclusion has been drawn that clinically relevant long-term (> 6 months) pain-relieving effects of acupuncture can be seen in a proportion of patients with nociceptive pain. The mechanisms behind such effects are considered here.

The acupuncture physiology is often summarised in the following manner: spinal gate-control mechanism and central β-endorphin elevation acting through the serotoninergic and/or noradrenergic descending system. There has also been claimed that DNIC is operating.

From the existing experimental data some important conclusions can be drawn: (1) much of the animal research only represents very short-term hypoalgesia; (2) almost all experimental acupuncture research has been performed with electro-acupuncture even though therapeutic acupuncture is mostly gentle manual acupuncture; (3) most of the experimental human acupuncture pain threshold (PT) research shows only fast and very short-term hypoalgesia, and, very important, PT elevation in humans does not predict the clinical outcome; (4) the effects of acupuncture ought to be divided into two main components – acupuncture analgesia and therapeutic acupuncture.

A new clinically based hypothesis on the mechanisms of therapeutic acupuncture will include: (1) peripheral events that might improve tissue healing and give rise to local pain relief through axon reflexes, the release of neuropeptides with trophic effects, and local endorphins; (2) spinal mechanisms that are involved such as the gate-control, long-term depression and the balance between long-term depression and long-term potentiation; (3) supraspinal mechanisms; (4) cortical, psychological, ‘placebo’ mechanisms from counselling, reassurance and anxiety reduction.