Clinically significant changes in pain along the Pain Intensity Numerical Rating Scale in patients with chronic low back pain

Low back pain (LBP) is the most common cause of chronic pain. Numerous clinical scales are available for evaluating pain, but their objective criteria in the management of LBP patients remain unclear. This study aimed to determine an objective cutoff value for a change in the Pain Intensity Numerical Rating Scale (Delta PI-NRS) three months after LBP treatment. Its utility was compared with changes in six commonly used clinical scales in LBP patients: Pain Disability Assessment Scale (PDAS), Pain Self-Efficacy Questionnaire (PSEC), Pain Catastrophizing Scale (PCS), Athens Insomnia Scale (AIS), EuroQoL 5 Dimension (EQ5D), and Locomo 25. We included 161 LBP patients treated in two representative pain management centers. Patients were partitioned into two groups based on patient's global impression of change (PGIC) three months after treatment: satisfied (PGIC = 1, 2) and unsatisfied (3-7). Multivariate logistic regression analysis was performed to explore relevant scales in distinguishing the two groups. We found Delta PI-NRS to be most closely associated with PGIC status regardless of pre-treatment pain intensity, followed by Delta EQ5D, Delta PDAS, Delta PSEC, and Delta PCS. The Delta PI-NRS cutoff value for distinguishing the PGIC status was determined by ROC analysis to be 1.3-1.8 depending on pre-treatment PI-NRS, which was rounded up to Delta PI-NRS = 2 for general use. Spearman's correlation coefficient revealed close relationships between Delta PI- NRS and the six other clinical scales. Therefore, we determined cutoff values of these scales in distinguishing the status of Delta PI-NRS >= 2 vs. Delta PI-NRS<2 to be as follows: Delta PDAS, 6.71; Delta PSEC, 6.48; Delta PCS, 6.48; Delta AIS, 1.91; Delta EQ5D, 0.08; and Delta Locomo 25, 9.31. These can be used as definitive indicator of therapeutic outcome in the management of chronic LBP patients.