Background aims:
Causes of chronic pain are postulated to lie in abnormal pain modulation apparent in many diseases. The nociceptive system is balanced with certain anti- and pro-nociceptive mechanisms. Former includes the spinal inhibitory network assessed by conditioned pain modulation. Latter is due to a sensitization along the nociceptive neuraxis leading to ectopic excitability, contributing to hyperalgesia and allodynia. Temporal summation of pain (TSP) reflects this central sensitization.

Methods:
This study assesses pain modulation during tonic noxious heat application in three groups: Thoracic spinal cord injury (SCI) patients with and without neuropathic pain (NP), and matched healthy controls. The assessment was performed at the volar forearm in order to investigate a sensory intact area. A thermode was heated to 45°C, and the participant was instructed to rate the pain on a numeric rating scale. Subsequently, they had to keep the pain level constant for two minutes by adjusting the temperature of the thermode (participant-controlled temperature, PCT). Clicking the mouse buttons increased or decreased the temperature, respectively.

Results:
The binary analysis of TSP occurrence highlighted that NP patients show the highest percentage of TSP occurrences (NP: 88%, nonNP: 63.6%, HC: 80%). Statistical analysis revealed a significant increase of the TSP magnitude and the TSP area under curve between the NP and nonNP SCI group.

Conclusions:
Increased temporal summation of pain – acting as a proxy for central sensitization - was found in SCI patients with chronic NP. The method of tonic heat profiles enables a continuous measure allowing the analysis of adaptation and the TSP processes.

01 - ASSESSMENT OF CENTRAL SENSITIZATION IN NEUROPATHIC PAIN FOLLOWING SPINAL CORD INJURY