Multimodal sensory evaluation of neuropathic spinal cord injury pain: an experimental study

Abstract

Study design: An experimental study.

Objectives: To investigate the changes in somatosensory functions using the combined application of quantitative sensory testing (QST), contact heat-evoked potentials (CHEPs) and laser-evoked potentials (LEPs) studies in individuals with spinal cord injury (SCI) in relation to neuropathic pain (NeP).

Setting: Centre for Pain Medicine, Swiss Paraplegic Centre, Nottwil, Switzerland.

Methods: Individuals with SCI were compared: 12 with NeP (SCI NeP) and 12 without NeP (SCI no NeP). Tools used were QST, CHEPs, LEPs and self-reported questionnaires. Tests were applied to the control (hand) and test (dermatome of altered sensation) sites, and compared to the able-bodied group.

Results: QST, LEPs and CHEPs assessments showed abnormalities both on the test and control sites, which did not differ between the groups with SCI. QST showed higher prevalence of allodynia in SCI NeP. CHEPs and LEPs demonstrated diminished amplitudes in both groups with SCI in comparison to able-bodied individuals. Only reaction time (RT) analysis revealed the difference of SCI NeP from the other two groups, expressed in partially preserved responses to the laser C-fibre stimulations.

Conclusions: Combination of assessments in our study allowed to examine spinothalamic and dorsal column functions in individuals with SCI. Changes in QST, CHEPs and LEPs were detected below the level of injury independent of NeP and at the control site indicating modifications in sensory processing rostral to the spinal lesion. Analysis of RT during laser stimulation could be an essential component when evaluating the somatosensory functions related to NeP in persons with SCI.

Fig. 1. Frequencies of abnormal quantitative sensory testing (QST) parameters.

Positive values indicate positive sensory signs (black bars, hyperaesthesia and hyperalgesia), whereas negative values indicate negative sensory signs (light grey bars, hypoaesthesia and hypoalgesia). Dashed lines: expected range for able-bodied participants (±2.5%). Insets show values for PHS and DMA parameters. Significance when compared to the normative values [23]: *p < 0.05, **p < 0.01, ***p < 0.001 (One-way t-test). a Control site (hand) QST parameters in SCI NeP (n = 12) b Test site (trunk, thigh or foot) QST parameters in SCI NeP. c Control site (hand) QST parameters in SCI no NeP (n = 12) d Test site (trunk, thigh or foot) QST parameters in SCI no NeP. SCI spinal cord injury, NeP neuropathic pain, CDT cold detection threshold, WDT warm detection threshold, TSL thermal sensory limen, CPT cold pain threshold, HPT heat pain threshold, PPT pressure pain threshold, MPT mechanical pain threshold, MPS mechanical pain sensitivity, WUR wind-up ratio, MDT mechanical detection threshold, VDT vibration detection threshold, PHS paradoxical heat sensations, DMA dynamic mechanical allodynia, CI confidence interval.

Fig. 2. Summary of late laser-evoked (LEPs) and contact heat-evoked potentials (CHEPs).

a Grand averages (black traces) and individual average LEPs (left panel, grey traces) and CHEPs (right panel, grey traces) waveforms from the control site (hand) measured in three groups: able-bodied (upper traces), SCI NeP (middle traces) and SCI no NeP (lower traces). Negative values are plotted upwards. Statistical mean values of the LEPs and CHEPs N2 and P2 latencies as well as N2P2 aplitudes were not different between the groups (p > 0.05, One-way ANOVA or Kruskal–Wallis one-way ANOVA on ranks). b Examples of LEPs (left panel) and CHEPs (right panel) waveforms measured from the test site (trunk, thigh or foot) from those individuals in SCI NeP (middle traces) and SCI no NeP (lower traces) groups, in whom LEPs and CHEPs were preserved (n = 3 for each group). The upper traces show examples of individual LEPs (left panel) and CHEPs (right panel) traces from three matching able-bodied participants. SCI spinal cord injury, NeP neuropathic pain, N2 negative component N2, P2 positive component P2.

Fig. 3. Reaction times of ultra-late laser-evoked potentials (ULEPs) inciting stimuli.

a (left panel) Reaction time (RT) distribution analysis for the control (left column) and test (right column) sites in all three groups: able-bodied participants (first panel), SCI NeP participants (second panel) and SCI no NeP participants (third panel). b Cumulative histogram plots for the able-bodied (black line), SCI NeP (dark grey) and SCI no NeP (light grey) groups. Both groups with SCI showed difference in RT distribution at the control (hand, *p < 0.05, Kolmogorov–Smirnoff test) and test sites (***p < 0.001, Kolmogorov–Smirnoff test) in comparison to the able-bodied group. SCI spinal cord injury, NeP neuropathic pain, Cum. freq. cumulative frequency, Norm. freq. normalized frequency.