Psychometric validation of two patient-reported outcome measures to assess symptom severity and changes in symptoms in hereditary angioedema.

PURPOSE: Hereditary angioedema (HAE) is a rare disorder characterized by highly variable, acute attacks of swelling at various anatomical locations. Clinical measures do not adequately assess the diversity of symptoms characteristic of an attack. Two disease-specific, patient-reported outcome measures were developed to comprehensively capture symptom severity and change: the Treatment Outcome Score (TOS) and the Mean Symptom Complex Severity (MSCS) score.

METHODS: This study comprised a secondary analysis of pooled data from a randomized controlled trial to evaluate the psychometric properties, including reliability and validity, and minimally important difference (MID) of the TOS and MSCS score.

RESULTS: HAE patients (n = 73) had a mean age of 33 years, and 60% were female. Test-retest evaluation demonstrated moderate to substantial agreement (ICCs = 0.53 for TOS; 0.62 for MSCS score). The TOS and change in MSCS score were moderately to highly correlated with a Global Improvement Measure at 4 h (TOS: r = 0.90; MSCS: r = -0.59). Anchor- and distribution-based analyses suggested that conservative estimates for MID are 30 points for TOS and -0.30 points for 4-h change in MSCS score.

CONCLUSIONS: The psychometric tests performed here provide evidence of the reliability and validity of the TOS and MSCS for evaluating symptom severity and change in HAE patients. The TOS and MSCS score provide an example of measurement methodology that may be used to precisely capture symptom severity and change in a disease characterized by acute attacks.