Factors related to agreement between self-reported and conventional Expanded Disability Status Scale (EDSS) scores

Background: Although the Expanded Disability Status Scale (EDSS) remains a widely used scale for evaluating impairments in people with multiple sclerosis (MS), EDSS assessments are infeasible in certain situations. A self-administered version of the EDSS would be potentially useful if it yielded similar results as the conventional physician-based version. Methods: We developed a self-administered patient questionnaire to obtain ratings of neurologic impairments, and developed algorithms to estimate EDSS scores. We mailed the questionnaires to all new consecutive patients scheduled to be seen at an MS clinic. Questionnaires were completed prior to the visit and traditional EDSS ratings were made by one of two neurologists at the visit. One hundred and forty-six pairs of patient questionnaires and physician EDSS assessments were obtained. Results: Kappa values for agreement between the physician's EDSS scores and the questionnaire-derived scores were 0.13 (for exact agreement), 0.39 (+/-0.5 EDSS steps), and 0.56 (+/-1.0 EDSS steps). A scatterplot showed that agreement was best at EDSS scores < 3.0 and > 5.0. Better agreement was obtained when patients had a higher level of education, and when the physician was more certain of the diagnosis of MS. Conclusions: While the self-assessed EDSS scores do not agree highly enough to take the place of conventional EDSS scores, they may be sufficient for MS trial screening or for assessing outcomes across broad categories of disability.