Estimation of the minimal important change for Brief Pain Inventory in patients with persistent spinal pain

The Brief Pain Inventory (BPI) is a widely used tool for assessing pain severity and interference, aligning with the bio-psycho-social model. It has been validated in various languages for patients with persistent spinal pain. However, the Minimal Important Change (MIC), which represents the smallest change perceived as meaningful by patients, has not yet been explored for this patient population.

This study aimed to estimate the MIC for the BPI-DK in patients with persistent spinal pain.

MIC was estimated using both anchor-based and distribution-based approaches. The anchor-based method was used to calculate mean changes in BPI-DK subscales for patients reporting improvement on the GROC scale. The distribution-based method estimated MIC as 1.96 times the standard error of measurement.

A total of 135 patients completed both baseline and 3-month follow-up questionnaires. Statistically significant MIC scores were found across all subscales. The MIC ranged from 1.37 to 2.61 for severity subscore, 1.59 to 2.91 for physical interference, 1.08 to 3.11 for affective interference, and 1.38 to 2.72 for overall interference subscore, depending on the method used.

This study establishes the MIC for the BPI-DK in patients with persistent spinal pain. Differences between the anchor-based and distribution-based methods highlight the sensitivity of the approach, with distribution-based estimates suggesting changes beyond measurement uncertainty. A 2-point improvement is recommended as clinically meaningful for this population.