Psychometric Properties of the SymptoMScreen Questionnaire in a Mild Disability Population of Patients with Relapsing-Remitting Multiple Sclerosis: Quantifying the Patient's Perspective

Abstract

Crucial elements for achieving optimal long-term outcomes in multiple sclerosis (MS) are patient confidence and effective physician-patient communication. Patient-reported instruments may provide the means to fill the gap in currently available clinician-rated measures. The SymptoMScreen (SMSS) is a brief self-assessment tool for measuring symptom severity in 12 neurologic domains commonly affected by MS. We conducted a non-interventional study to assess the dimensional structure and item characteristics of the SMSS. A total of 218 patients with relapsing-remitting MS and mild disability (median Expanded Disability Status Scale score 2.0) were studied. Symptom severity was low (SMSS score 13.5, interquartile range 4.2-27), fatigue being the domain with the highest impact. A non-parametric item response theory, i.e., Mokken analysis, found that the SMSS is a robust one-dimensional scale (overall scalability index H 0.60) with high reliability (Cronbach's alpha 0.94). The confirmatory factor analysis model confirmed the unidimensional structure (comparative fit index 1.0, root-mean-square error of approximation 0.001). Samejima's model fitted well an unconstrained model with different item difficulties. The SMSS shows appropriate psychometric characteristics and may constitute a valuable and easy-to-implement addition to measure the symptom severity in clinical practice.