Clinical Characteristics Associated with the PLP-PLS Index, a New Potential Metric to Phenotype Phantom Limb Pain

Background: Phantom limb pain (PLP) is highly prevalent after amputation. However, the influence of non-painful sensations (PLS) remains unclear. This study examines the PLP-PLS index as a novel tool to differentiate PLP from PLS and explores the association of clinical factors with the index. Methods: We conducted a cross-sectional analysis of baseline data from 112 participants in a previous factorial trial in patients with unilateral traumatic lower limb amputation. Linear regression models were used to examine the associations between the index and various demographic, psychological and clinical factors. Logistic and Poisson regression, and e-value calculation were utilized for sensitivity analyses. Results: Adjusted multivariable linear regression models demonstrated significant associations of phantom movement sensation (β: −1.532; 95% CI: −2.615 to −0.449; p = 0.006) and time since amputation (β: 0.005; 95% CI: 0.0006 to 0.0101; p = 0.026) with the PLP-PLS index. These findings were confirmed by multivariable logistic regression (phantom movement sensation OR: 0.469; 95% CI: 0.200 to 1.099, p = 0.082; time since amputation OR: 1.003; 95% CI: 1.00003 to 1.007; p = 0.048) and sensitivity analyses. Conclusions: Time since amputation and phantom movement sensation likely reflect distinct phenotypes and potential mechanisms for PLP and PLS. The PLP-PLS index is a promising clinical tool for selecting therapies to prevent/treat PLP and for measuring treatment effects to modulate phantom pain. These findings emphasize the importance of understanding the mechanisms underlying PLP and PLS for improving clinical management and guiding future research.