BACKGROUND: Pachyonychia congenita (PC) is a rare but often debilitating, dominantly inherited disorder. New treatments require more accurate instruments for evaluating changes in the quality of life in these patients.
OBJECTIVES: This study was undertaken to develop and validate a quality of life questionnaire for PC patients (PCQoL).
METHODS: Relevant factors influencing quality of life in PC patients were identified and incorporated into the well-recognized, general questionnaire, the Dermatology Life Quality Index (DLQI), to establish a disease-specific measure, the PCQoL. Classical test theory (CTT) and Rasch analysis (RA) were used to analyze and validate the PCQoL.
RESULTS: CTT analysis established test-retest reliability and internal consistency for the PCQoL. Concurrent and construct validity for the DLQI and the PCQoL were also validated. Chi-square-based infit and outfit statistics indicated that the Rasch model fits the observed responses very well. RA reconfirmed reliability, internal consistency, reasonable homogeneity, construct validity, and the presence of three RA-based domains.
CONCLUSION: The PCQoL questionnaire is a measure validated by both CTT and RA. It appears to be a valuable tool in measuring quality of life modifications in PC individuals with keratoderma.