Objective: To prospectively characterize the relation between two-year changes in functional impairment as measured by the Multiple Sclerosis Functional Composite (MSFC) and changes in patient perceived disability as measured by the Guy's Neurological Disability Scale (GNDS).
Methods: One hundred and eighty-eight patients with multiple sclerosis (MS) were recruited at our outpatient clinic. Impairment and disability were assessed using the MSFC and GNDS at baseline and follow-up. Longitudinal correlations were studied between changes in MSFC and GNDS and their corresponding components. We also studied changes in GNDS in relation to what can be classified as a reliable change in MSFC; for example, 20% change in each MSFC component or a change of 0.5 in total MSFC score. In addition, we studied the change in total number of GNDS subcategories with a score of 3 or higher in relation to the predefined MSFC changes, these subcategories being indicative of the requirement for help by another person.
Results: Despite good cross-sectional correlations between MSFC and GNDS, no significant correlation was found between longitudinal changes in MSFC and GNDS. Analysing the change in GNDS in relation to the predefined MSFC changes shows that GNDS changes are nicely rank ordered when more stringent definitions of reliable change were applied. In addition, analysing the number of GNDS subcategories scored 3 or higher indicate that there is a profile of worsening on the MSFC being associated with increase in the amount of help required from others.
Conclusion: Our longitudinal data suggest that a reliable change is associated with a likewise change in patient perceived disability, the smallest reliable change being identified by at least 20% change in each MSFC component.