Evolution of the Modified Rankin Scale and Its Use in Future Stroke Trials

Abstract

W ho would have guessed that a scale introduced by Dr John Rankin in 1957 would become the primary outcome scale for almost all acute stroke trials? 1 The Rankin Scale was modified to its current form by Charles Warlow and others as part of the UK-TIA (United Kingdom Transient Ischaemic Attack) trial in the 1980s, 2 and its reproducibility was first examined by van Swieten et al, in 1988 (Table 1). 3 There is no perfect stroke outcome scale.Regardless, the 7-level, modified Rankin Scale (mRS) has several major strengths: it covers the entire range of functional outcomes from no symptoms to death, its categories are intuitive and easily grasped by both clinicians and patients, its concurrent validity is demonstrated by strong correlation with measures of stroke pathology (eg, infarct volumes) and agreement with other stroke scales, 4 and its use has demarcated effective and ineffective acute stroke therapies in trials with appropriately powered sample sizes.With a limited number of levels, the mRS may be less responsive to change than some other stroke scales; however, a single-point change on the mRS is clinically relevant. 4limitation of the mRS has been the subjective determination between categories and the reproducibility of the score by examiners and patients.4 A systematic review and metaanalysis of studies describing interobserver variability of the mRS reports pooled reliability across 10 published studies (n=587 patients) of a κ=0.46 and a weighted κ of 0.90. 5 Multimedia training and certification of examiners in the use of the mRS (http://rankinscale.org/), structured interviews and questionnaires, [6][7][8][9][10] and centralized review of videotape assessments 11 have sought to address these issues, but reproducibility remains a concern.But the challenge for a trialist designing a new acute stroke trial is not whether to use the mRS as a primary or major secondary outcome measure, but what statistical approach to use to analyze the mRS, what to expect in terms of effect size, and how to communicate the results of a trial.These decisions are critical for determination of sample size, power, and implementation of study results into clinical practice when the trial is completed.