Validation of a novel scale for outcome measurement in Functional Neurological Disorder: The Functional Neurological Disorders Rating Scale (FuNDRS)

Functional Neurological Disorder (FND) is a common and disabling condition lacking an outcome measurement tool to guide efficacies of interventions in clinical trials. The Functional Neurological Disorders Rating Scale (FuNDRS) is a 25-item clinician-rated scale that generates scores across all symptom domains in FND and is designed to detect true symptom progression with sensitivity to change. This study demonstrates the initial validity of the FuNDRS using convergent, concurrent, discriminant, predictive and known-groups validity. Additionally, factor analysis, internal consistency, sensitivity to change and inter-rater reliability analyses are reported to further accrue evidence for validity. Collection of data in the day hospital arm (n=59) included FuNDRS, HoNOS, CGI-I, BDI, BAI, WSAS, PHQ-9 and GAD-7. Collection of data in the inpatient arm (n = 39) included FuNDRS, CGI S and CGI-I. Data analysis was performed using Pearson’s correlations, t-tests, quadratic weighted kappa and intra-class coefficient, and a principal components analysis. The FuNDRS has good internal consistency (α = 0.81) and showed overall strong positive correlation with the HoNOS and CGI (r > 0.6). Most items assessed for concurrent and discriminant validity displayed moderate to strong correlation. Patients scored lower at discharge, reflecting a statistically significant average difference of -12.41 (SE = 0.83) BCa 95% CI [10.77,14.05], resulting in a very large effect size of d = 8.19. The MDC95 was 2.3. Inter-rater reliability analysis was conducted on a subsample of inpatients found statistically significant agreement between two raters. Substantial agreement (Weighted Kappa > 0.8) occurred for change in scores on the FuNDRS and CGI scales. These findings support the initial validity of the FuNDRS as an outcome measurement tool for FND.