Evaluating cognitive outcome measures for MS clinical trials: what is a clinically meaningful change?

Brief cognitive assessments are increasingly emphasized in MS treatment studies and clinical care. While much is known about the reliability of several widely-used neuropsychological tests, interpretation of the changes in individual patients is inadequate. The FDA offers guidance on the issue, as related to patient-reported outcomes. Unfortunately, cognitive ability is only weakly correlated with the frequency and severity of self-reported cognitive problems. In this review, we critically examined the psychometrics of neuropsychological testing in MS, emphasizing statistical and anchor-based approaches to interpreting clinically meaningful change. We suggest that there are two paths forward that should be currently pursued. First, to employ co-primary outcomes, including a brief cognitive test and a clinician or observer's impression on a scale of change, where successful treatment would require showing significant improvement in both measures. Secondly, to work toward showing that when reliable brief cognitive tests are employed, increments of statistically-relevant change would correlate with changes in clinically-relevant anchors (such as vocational disability or clinical relapses with cognitive impairment). The latter goal will allow a more parsimonious and scientifically efficient approach of utilizing only the brief cognitive test as a primary outcome. While some progress has been made in this direction, more research is needed. We are of the opinion that data from both the statistical and clinically meaningful approaches will be necessary to develop valid definitions of meaningful change on cognitive outcome measures, and that it would be best to pursue research using tests that already have well-established reliability and validity.