"Summary measure" statistic for assessing the outcome of treatment trials in relapsing-remitting multiple sclerosis

A multiple sclerosis disease progression measure based on cumulative disability

BACKGROUND

Existing severity measurements in multiple sclerosis (MS) are often cross-sectional, making longitudinal comparisons of disease course between individuals difficult.

OBJECTIVE

The objective of this study is to create a severity metric that can reliably summarize a patient's disease course.

METHODS

We developed the nARMSS - normalized ARMSS (age-related MS severity score) over follow-up, using the deviation of individual ARMSS scores from the expected value and integrated over the corresponding time period. The nARMSS scales from -5 to +5; a positive value indicates a more severe disease course for a patient when compared to other patients with similar disease timings.

RESULTS

Using Swedish MS registry data, the nARMSS was tested using data at 2 and 4 years of follow-up to predict the most severe quartile during the subsequent period up to 10 years total follow-up. The metric used was area under the curve of the receiver operating characteristic (AUC-ROC). This resulted in measurements of 0.929 and 0.941. In an external Canadian validation cohort, the equivalent AUC-ROCs were 0.901 and 0.908.

CONCLUSION

The nARMSS provides a reliable, generalizable and easily measurable metric which makes longitudinal comparison of disease course between individuals feasible.

Benefits of glatiramer acetate on disability in relapsing-remitting multiple sclerosis. An analysis by area under disability/time curves. The Copolymer 1 Multiple Sclerosis Study Group

New immunomodulatory therapies for relapsing-remitting multiple sclerosis (RRMS) have well-documented effects in reducing relapses, but it has been difficult to demonstrate their benefits on disability in relatively short treatment trials. Commonly utilised disability outcome measures are problematic both in usefulness and clinical interpretation when applied to MS subjects with fluctuating and variable disease courses. An alternative technique is to use the summary measure 'area under the disability/time curve' (AUC) to index the total in-trial morbidity experienced by patients. In this study, we applied AUC analyses to the serial Expanded Disability Status Scale (EDSS) scores from the U.S. multicentre, Phase III, two-year core study of glatiramer acetate in 251 RRMS patients. When all available EDSS evaluations were analysed with AUC(CHANGE) ('combined data', including relapse-related assessments), active treatment was significantly superior to placebo (P=0.018). The benefits of glatiramer acetate persisted when transient relapse effects were reduced by using 'scheduled visit data' only (P=0.021). With the more conservative AUC(SUM) measure, significant active treatment effects remained (P=0.029 and 0.046, for both 'combined' and 'scheduled visit' data, respectively). Subgroup calculations performed with baseline disability stratified at EDSS 3.5 also showed benefits of treatment over placebo, but statistical significance was not reached. This analysis of data from a Phase III treatment trial illustrates the AUC summary measure technique and provides further evidence of the efficacy of glatiramer acetate in RRMS.

Disability outcome measures in therapeutic trials of relapsing-remitting multiple sclerosis: effects of heterogeneity of disease course in placebo cohorts

OBJECTIVES

Recent phase III clinical trials of immunomodulatory therapies in relapsing-remitting multiple sclerosis have shown significant benefits of active treatment on relapse related end points, but effects on disability outcomes have been inconsistent. These apparent discrepancies could be due to differences in the clinical end points employed, the behaviour of placebo cohorts, or both.

METHODS

Disability data from the placebo cohorts of two large phase III studies, the United States glatiramer acetate trial (Copolymer 1 Multiple Sclerosis Study Group) and the multinational interferon beta-1a trial (PRISMS Study Group) were combined and masked (n = 313). Two groups of disability outcome measures were assessed. Firstly, measures of disability change (2 year EDSS difference and area under the EDSS/time curve, AUC) were calculated. Secondly, conventional disease progression end points ("confirmed progression" and "worsening to EDSS 6.0") were evaluated by using Kaplan-Meier analysis and compared with a categorical classification based on EDSS trends.

RESULTS

The average increase in disability for the entire cohort as assessed by mean 2 year EDSS change (<0.5 EDSS point) or mean AUC (+0.57 EDSS-years) was small. For the "confirmed progression" end points, increasing the stringency of the definition lowered their incidence (from 32% with 1.0 point at 3 months, to 9% with 2.0 points at 6 months), but did not improve the positive predictive accuracy for "sustained progression" maintained to the end of the study. The error rate for this outcome was about 50%. Worsening to EDSS 6.0 was a more reliable end point, but had even lower sensitivity (incidence <10%). EDSS trend analysis showed markedly heterogeneous disease courses, which were then categorised into "stable" (26%), "relapsing-remitting" (59%), and "progressive" (15%) courses. Patients with the last course had deteriorated considerably by the end of 2 years (mean worsening of 2.0 EDSS points).

CONCLUSION

In relapsing-remitting multiple sclerosis treatment trials, the conventional measure of mean EDSS change has low sensitivity, whereas the widely applied confirmed progression end points have high error rates regardless of their definition stringency. Alternative methods with better data utilisation include AUC summary measures and categorical disease trend analysis. The heterogeneity of disability outcomes in short trials, combined with unreliable clinical end points, diminishes the credibility of therapeutic claims aimed at reducing irreversible neurological deficits. The behaviour of patients treated with placebo should be carefully analysed before conclusions are drawn on the efficacy of putative treatments.