Responsiveness to Change of the Morphea Activity Measure in Pediatric Patients.

Importance: Detecting activity of morphea can be complex but is crucial for adequate treatment and outcome assessment. The Morphea Activity Measure (MAM) was recently validated, but its responsiveness to change in disease activity has not been studied.
Objective: To evaluate the internal and external responsiveness of MAM to changes in disease activity in pediatric patients.
Design, Setting, and Participants: This multicenter prospective, longitudinal prognostic study was performed from October 2021 to January 2023 at 4 pediatric referral centers in North America. Consecutive pediatric patients with morphea who were available for data collection at baseline and at a follow-up visit at least 3 months later were studied.
Exposure: Patient demographics, clinical characteristics, and measurements of disease activity collected at baseline and the subsequent visit.
Main Outcome and Measures: Responsiveness of MAM to disease activity according to the modified Localized Scleroderma Severity Index (mLoSSI), the Physician Global Assessment (PGA), and a patient and parent global assessment (PtGA) was analyzed using mean and percentage change, standardized effect size, and standardized response mean (SRM) from baseline to follow-up 3 or more months later. Differences between patients whose activity improved vs did not improve were evaluated using the Mann-Whitney U test. The correlation between percentage change in MAM score and mLoSSI, the PGA, and the PtGA was calculated using Spearman rank correlation.
Results: A total of 43 patients (mean [SD] age at onset, 7.11 [3.18] years; 26 [60.5%] female) were included. The mean change and percentage change in MAM score were significantly larger in those whose disease activity improved by the PGA (mean: -18.75 [95% CI, -31.92 to -5.57] vs 2.73 [95% CI, -1.97 to 7.45]; percentage: -108.08% [95% CI, -155.21% to -60.95%] vs -24.11% [95% CI, -81.22% to 32.99%]) and by mLoSSI (mean: -24.15 [95% CI, -41.89 to -6.41] vs -1.30 [95% CI, -8.50 to 5.70]; percentage: -172.06% [95% CI, -263.68% to -80.45%] vs -21.57% [95% CI, -48.13% to 4.97%]) than in those whose activity did not change. The SRM of MAM was significantly different between groups for both measures; the responsiveness was large in those whose activity decreased by the PGA (-0.75 [95% CI, -1.29 to -0.22]) and mLoSSI (-0.97 [95% CI, -1.69 to -0.25]) and none to small in those whose activity did not change by the PGA (0.11 [95% CI, -0.08 to 0.30]) or mLoSSI (-0.05 [95% CI, -0.34 to 0.23]). Percentage change in MAM score correlated strongly and significantly with change in mLoSSI (ρ = 0.69; P < .001) and PGA (ρ = 0.65; P < .001), but there was no correlation with change in the PtGA (ρ = 0.26; P = .09).
Conclusions and Relevance: In this prognostic study, MAM was found to be internally and externally responsive to changes in disease activity. Further evaluation in mixed cohorts of all ages and specialties is needed.