Purpose: To build a questionnaire to assess health-related quality of life (HRQL) in patients suffering from slowly progressive neuromuscular disease (NMD) using item response theory (IRT).
Methods: A pool of 64 items and a validated questionnaire (WHOQOL-BREF) were administered to 159 patients recruited in eight NMD referral centers. Exploratory statistical analysis included methods derived from both IRT and classical test theory.
Results: We constructed a questionnaire named QoL-NMD which is composed of two general items and 24 items classified in three domains: (1) "Impact of Physical Symptoms," (2) "Self-perception" and (3) "Activities and Social Participation." Each domain has good psychometric properties (Cronbach's alpha > 0.77, test-retest ICC > 0.81, Loevinger's H > 0.41) and meets IRT assumptions. Comparison with the WHOQOL-BREF enabled assessing similarities and discrepancies with a generic questionnaire.
Conclusion: This study enabled the development of a new HRQL questionnaire specifically designed for slowly progressive NMD patients. The QoL-NMD is short enough to be used in clinical practice (26 items). The next steps will be to validate QoL-NMD by re-assessing psychometrics in an independent sample of patients and calibrate the IRT scoring system.
Keywords: Item response theory; Neuromuscular disease; Outcome research; Patient outcome assessment; Quality of life.