Minimum clinically important difference (MCID) of the personal impact of epilepsy scale (PIES).

Introduction: The Personal Impact of Epilepsy Scale (PIES) assesses patient functional status in subscales of (1) seizure impact, (2) medication effects, (3) mood & social status, and (4) overall quality of life. This study was designed to determine the Minimal Clinically Important Change (MCID) in PIES subscale and total scores that demonstrate improvement.

Methods: To ascertain the correspondence of PIES score change and clinical status change (improved, same, worse) in each PIES subscale and total score, we used two distinct retrospective anchor-based assessments of clinical status (patient self-assessment and trained rater assessment) across two clinic visits. Mean PIES scores were compared between clinical status groups, controlling for days between visits and initial clinical status. Personal Impact of Epilepsy Scale score change was quantified for each group to determine MCID. A small prospective proof-of-concept study was conducted in a separate subject group.

Results: Patient self-report anchor analysis demonstrated lower (better) PIES scores in the "improved" group vs the "worse" group on the mood & social subscale (p < .001) and total score (p = .002), with a similar trend on the seizure subscale (p = 0.056). Clinical rater anchor analysis demonstrated lower PIES scores in the "improved" vs "worse" group in the mood & social subscale (p = .029) and a trend in total score (p = .082). For the "improved" group, the reduction in PIES scores between visits averaged across both anchor analyses was 8.14% for subscales and 8.67% for total score.

Discussion/conclusion: Reduction of 8% on a PIES subscale or total score indicates meaningful improvement in patient clinical status, and is designated the MCID for this instrument. Personal Impact of Epilepsy Scale can be useful in day-to-day clinical care and as an outcome metric in clinical research.