Thermal Grill Illusion in Chronic Lower Back Pain: A Case-Control Study

Abstract

Purpose This study aimed to use thermal grill illusion (TGI), an experimental model of pain processing and central mechanisms, to evaluate the perception of TGI-related sensations or pain in patients with chronic lower back pain (CLBP). Patients and Methods The perception of TGI (warmth/heat, cold, unpleasantness, pain, burning, stinging, and prickling) was examined in 66 patients with CLBP and compared with that in 22 healthy participants. The visual analog scale (VAS) scores for CLBP, Oswestry Disability Index (ODI), and 12-Item Short Form Survey (SF-12) scores were obtained from the included patients with CLBP. Results The CLBP group showed a less intense perception of TGI for sensations of warmth/heat, unpleasantness, and pain than the control group. The CLBP group felt burning sensations lesser than the control (2.77 vs 4.55, P=0.016). In the CLBP group, there were significant correlations between the ODI and the degree of unpleasantness (r=0.381, P=0.002) and prickling sensation (r=0.263, P=0.033). There were also significant correlations between the mental component score of the SF-12 and the degree of warmth/heat (r=−0.246, P=0.046), unpleasantness (r=−0.292, P=0.017), pain (r=−0.292, P=0.017), and burning sensations (r=−0.280, P=0.023). Conclusion Our results may be useful for clinicians to evaluate the effectiveness of drugs or interventions to manage centralized LBP.

Assessing Individual Sensitivity to the Thermal Grill Illusion: A Two-Dimensional Adaptive Psychophysical Approach

“…The ability to adaptively titrate the TGI through psychophysical staircasing is particularly relevant for clinical studies involving between-group comparisons. Previous studies investigating whether TGI is enhanced or reduced in specific clinical populations failed to account for the inter-individual differences in thermal sensitivity (e.g., [21,22]). Given the proposed role of TGI as a model for chronic pain in conditions such as central neuropathic [37,38] and nociplastic pain [11,29], adopting an approach that captures the entire spectrum of individual responses to TGI is crucial for elucidating its significance in clinical settings.…”

“…Progress in our understanding of the TGI has been constrained by a narrow focus on predetermined stimulation parameters, as for example temperatures of 20°C and 40°C [4,5,[9][10][11][12][13][14][15][16] or values that deviate by only one or two degrees Celsius from this standard set of cold and warm temperatures [17][18][19][20][21][22]. The reliance on fixed temperature combinations overlooks inter-individual variability in thermal perception and has led to an overly simplistic categorization of individuals as responders or non-responders [14,[23][24][25][26][27], without an adequate characterization of variability in temperature parameters at which the illusion manifests.…”