Detecting abnormal central pain processing

Peripheral and central sensitization are important factors which may induce pain chronicity. In healthy subjects, the central nervous system is capable of decreasing pain intensity when repetitive painful stimuli are applied due to endogenous pain inhibition and central pain signal modulation. Another term for adaptation to continuously applied pain stimuli is habituation. So far, pain research used the individual subjective pain rating (numeric analogue scale, visual analogue scale) to visualize habituation (decrease of subjective pain over time).

A new scientific approach is the induction of central habituation by repetitive painful laser stimuli, which are synchronized with EEG to analyse Laser-evoked potentials (LEP). Repetitive painful laser stimuli induce a continuous decrease of the subjective pain rating and the LEP-amplitude over time, i.e. LEP-habituation. This LEP-habituation phenomenon affects both hemispheres as well as the central signal processing of different nerve fibre sub-classes.

In patients with nociceptive and neuropathic pain, LEP-habituation is substantially reduced in comparison to healthy controls, which points to an abnormal central pain processing. Central sensitization seems to oppose physiological LEP-habituation.


Figure 3: The comparison of LEP-habituation of painful radiculopathy patients versus healthy controls is shown here. Reduced LEP-habituation was found in the patient group as sign of abnormal central pain processing. Patients with signs of central sensitization showed a further decreased LEP-habituation indicating that central sensitization seems to be a major contributor of abnormal central pain processing.

The present project investigates whether the assessment of LEP-habituation may be used as diagnostic tool in order to detect abnormal central pain processing electrophysiologically. Being able to document abnormal central pain processing, might enable clinicians to drive treatment decisions in the direction of centrally acting analgesic drugs. The further, the restitution of LEP-habituation might document treatment success