Discrepancies in Describing Pain: is There Agreement Between Numeric Rating Scale Scores and Pain Reduction Percentage Reported by Patients with Musculoskeletal Pain After Corticosteroid Injection?

Objective: Pain intensity is commonly rated on an 11-point Numerical Pain Rating Scale which can be expressed as a calculated percentage pain reduction (CPPR), or by patient-reported percentage pain reduction (PRPPR). We aimed to determine the agreement between CPPR and PRPPR in quantifying musculoskeletal pain improvement at short-term follow-up after a corticosteroid injection.

Design: Retrospective cohort study.

Setting: Urban, academic, physical medicine, and rehabilitation outpatient interventional musculoskeletal and spine center.

Methods: The agreement between CPPR and PRPPR was determined by concordance correlation coefficient (CCC) in subjects who had experienced improvement in musculoskeletal or radicular pain 3 weeks after a first-time injection at our clinic. Subjects who experienced unchanged pain (PRPPR = 0) were compared to CPPR with paired t-test.

Results: We examined 197 subjects with greater than 3/10 pain who underwent first-time fluoroscopic-guided corticosteroid injections. Ninety-three subjects reported higher PRPPR than CPPR values, and 41 subjects reported higher CPPR values. The CCC between CPPR and PRPPR was 0.44 (95% CI 0.35-0.54), with a precision of 0.54 and an accuracy of 0.81, and 95% limits of agreement ranging between -41% and +73%. Values for CCC, precision, and accuracy were higher for males compared to females and were highest in the youngest age group (18-40) and lowest in the middle age group (41-60).

Conclusions: PRPPR may not agree with CPPR at 3 week follow-up, as these individuals tend to report a higher estimated percentage improvement compared to the value calculated from their pain scores.