Allodynia and hyperalgesia – may be signs of central sensitisation…
Although the terms “wind up” and central sensitisation are often used synonymously, although they are not strictly equivalent. Wind up will occur in response to any painful stimulus and would normally resolve over time. Central sensitisation can be thought of as wind up that has not wound down and represents a chronic pain state.
In practical terms central sensitisation may be identified in our patients by the presence of allodynia and, to a lesser extent hyperalgesia. Allodynia refers to when a normally non-noxious stimulus (touch for example) is perceived as pain. Hyperalgesia is an exaggerated response to a painful stimulus, and is therefore rather harder to be certain about.
Allodynia will be missed if the examination of the patient involves immediate firm palpation, such as grasping a limb and manipulating the joint – all the examiner will discern is pain, although it will not necessarily correlate with the movement of the joint and may therefore be confusing.
A light touch over the whole patient prior to deeper palpation will reveal suferficial allodynia by a sharp or shrinking movement away from the touch, fasiculations and tremor, as well as other more obvious pain responses.
Needling an area of superficial allodynia will generally be resented and is likely to make the pain condition worse. If the area is localized, then the following approaches can be tried:
In practice, those patients who just seem to get worse with acupuncture and do not improve may have central sensitisation, and their pain condition should be reviewed with this in mind.