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Sample size estimates for determining treatment effects in high-risk patients with early relapsing-remitting multiple sclerosis

Drexel University College of Medicine, Department of Neurology, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA, tscott{at}wpahs.org

Carol J Schramke

Drexel University College of Medicine, Department of Neurology, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

Gary Cutter

Center for Research Design and Statistical Methods, University of Nevada School of Medicine, Reno, Nevada, USA

Background: Risk factors for short-term progression in early relapsing-remitting MS have been identified recently. Previously we determined potential risk factors for rapid progression of early relapsing-remitting MS and identified three groups of high-risk patients. These non-mutually exclusive groups of patients were drawn from a consecutively studied sample of 98 patients with newly diagnosed MS. High-risk patients had a history of either poor recovery from initial attacks, more than two attacks in the first two years of disease, or a combination of at least four other risk factors. Objective: To determine differences in sample sizes required to show a meaningful treatment effect when using a high-risk sample versus a random sample of patients. Methods: Power analyses were used to calculate the different sample sizes needed for hypothetical treatment trials. Results: We found that substantially smaller numbers of patients should be needed to show a significant treatment effect by employing these high-risk groups of patients as compared to a random population of MS patients (e.g., 58% reduction in sample size in one model). Conclusion: The use of patients at higher risk of progression to perform drug treatment trials can be considered as a means to reduce the number of patients needed to show a significant treatment effect for patients with very early MS.

Key Words: multiple sclerosis • prognosis • risk factors • sample size

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