Abstract

Background: The Psychogenic Movement Disorders Rating Scale (PMDRS) has potential as a useful objective assessment in clinical research, but the current scale has limitations. We developed a simplified version (S-FMDRS) and assessed inter-rater reliability, concurrent validity, and sensitivity. Methods: Fifty-two videos of subjects with functional (psychogenic) movement disorders (FMD) were rated according to the PMDRS and S-FMDRS by three neurologists. Inter-rater reliability was assessed using intraclass correlation coefficient (ICC). Agreement of symptomatic body regions and movement disorder classification was assessed using Light's kappa. Spearman's correlation coefficient was used to assess concurrent validity. A physiotherapist also rated videos on the S-FMDRS. The simplified scale was piloted in a feasibility study of physiotherapy for FMD to assess sensitivity. Results: ICC of total scores was 0.84 for the original scale and 0.85 for the simplified scale. Light's kappa for agreement of symptomatic body regions and movement disorder classification was moderate to low. Concurrent validity was demonstrated by Spearman's correlation between the two scales ranging from 0.84 to 0.95. The simplified scale was sensitive to change, with an effect size in the feasibility study of 0.79. Inter-rater reliability between physiotherapist and neurologist was high (ICC 0.85). Discussion: Both versions of the scale had good inter-rater reliability for the total score. Low agreement on movement disorder classification and identification of symptomatic body regions support our argument for a simplified scale. Conclusions: The S-FMDRS has high inter-rater reliability and good sensitivity to change. Further psychometric evaluation is warranted.