Novel activity and participation scales for children, adolescents, and young adults with postacute infection and vaccination syndromes and/or ME/CFS.

Children, adolescents, and young adults (CYP) with postacute infection and vaccination syndromes (PAIVS), and/or myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), experience profound loss in activity and participation. We introduce and psychometrically validate two new brief, age-adapted, and domain-specific questionnaires for clinical use assessing activity and participation in this vulnerable patient group. For this, 91 patients (aged 10-25 years) were assessed at the Munich Chronic Fatigue Center (MCFC) from 12/2022 to 11/2024. We designed the MCFC Activity Scale and MCFC Participation Scale and assessed construct validity using confirmatory factor analysis for both questionnaires. Reliability was evaluated via Cronbach's α. Factor-based MCFC Activity and Participation Scores (0-100) were derived and correlated with Bell Score, FSS, DSQ-PEM, and SF-12 Component Summary Scales (PCS and MCS). Discrimination for ME/CFS was evaluated using ROC analyses. Participants (mean age 15.6 ± 2.4 years) were predominantly female (64%). 65% were diagnosed with ME/CFS. The MCFC Activity Scale showed excellent one-factor fit (comparative fit index, CFI = 1.00) and good internal consistency (α = 0.82). The MCFC Participation Scale showed good internal consistency (α = 0.85) and acceptable one-factor fit (CFI = 0.817). Factor-based activity and participation were strongly correlated yet distinct (r = 0.73). Derived MCFC Activity and Participation Scores differed significantly by ME/CFS diagnosis (p ≤ 0.009). Scores correlated with Bell Score, FSS, DSQ-PEM, and SF-12 PCS (all p ≤ .002). For ME/CFS discrimination, the Activity Score achieved an AUC = 0.78 and the Participation Score an AUC = 0.72.Conclusion: The Activity Scale demonstrated strong construct validity. The Participation Scale showed good internal consistency. Both scores demonstrated good convergent validity with established patient-reported outcome measures, supporting clinical utility. They may serve as pragmatic screening tools for this vulnerable patient group.