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

Abstract 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. What is Known: • PAIVS and ME/CFS are debilitating diseases that lead to substantial loss in daily activity and social participation. • Assessing limitations in activity and participation is important for clinical decision-making and disease monitoring. What is New: • The novel MCFC Activity and Participation Scales are brief, age-adapted, and domain-specific questionnaires assessing activity and participation in young people with PAIVS and ME/CFS. • Both questionnaires are valid and reliable instruments. They may serve as clinically usable tools to improve patient care in this vulnerable group.