Longitudinal Changes in Somatosensory Function and Their Association with Pain Trajectory Groups in a Portuguese...

Background: Cancer-related pain involves complex peripheral and central mechanisms. Quantitative sensory testing (QST) assesses somatosensory function and provides insights into pain mechanisms. However, longitudinal evidence in oncological populations remains limited. This study investigated longitudinal changes in somatosensory function and their relationship with pain intensity and pain trajectory groups in a Portuguese cancer cohort. Methods: This longitudinal study was conducted within the international PAINLESS project and included participants from the Portuguese clinical unit. A total of 56 cancer patients were assessed at diagnosis (baseline, T0), before treatment, and at 6-month follow-up (T6). Pain intensity was measured using the Numeric Rating Scale (NRS), and somatosensory function was assessed using standardized thermal QST, including heat pain threshold (HPT), cold detection threshold (CDT), cold pain threshold (CPT), temporal summation of pain (TSP), and conditioned pain modulation (CPM). Non-parametric analyses evaluated longitudinal changes, correlations between pain and QST measures, differences according to clinically relevant pain (NRS < 4 vs. ≥ 4), and differences across clinically meaningful pain trajectory groups. Results: Thermal sensory thresholds changed significantly, with decreased HPT (p = 0.025) and increased CDT (p < 0.001) and CPT (p = 0.005). At T0, pain intensity was negatively correlated with CDT (r_s = - 0.371, p = 0.009), whereas at T6 it was positively correlated with CPT (r_s = 0.401, p = 0.006). Longitudinal changes in pain intensity were also associated with changes in CPT (r_s = 0.337, p = 0.029). Trajectory analysis demonstrated significant baseline CDT differences across pain trajectory groups (p = 0.028), with higher CDT values in the pain increase group than in the persistent pain group (adjusted p = 0.035). No significant longitudinal changes were observed in central pain modulatory measures (TSP and CPM). Conclusions: Altered thermal sensory processing, particularly cold-related measures, was associated with pain intensity and trajectories during the first six months after diagnosis. While central pain modulation remained stable, CDT and CPT showed consistent relationships with clinically relevant pain outcomes. These findings support the potential utility of thermal QST for characterizing sensory profiles and pain trajectory groups in cancer-related pain; being important, further longitudinal studies are needed to determine the predictive value of these measures.