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Clinical outcomes assessment in multiple sclerosis.

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SPECIAL REPORT
Clinical Outcomes Assessment
in Multiple Sclerosis
Richard Rudick, MD,* Jack Antel, MD,f Christian Confavreux, MD,$ Gary Cutter, PhD,$
George Ellison, MD,? Jill Fischer, PhD,* Fred Lublin, MD,** Aaron Miller, MD,?? John Petkau, PhD,$$
Stephen Rao, PhD,$s Stephen Reingold, PhD,SJ Karl Syndulko, PhD,*** Alan Thompson, MD,?H
Joy Wallenberg, MD,+$$ Brian Weinshenker, MD,S$S and Ernest Willoughby, MDSSS
This article represents initial deliberation of an international task force appointed by the US National Multiple Sclerosis
Society to develop recommendationsfor optimal clinical assessment tools for multiple sclerosis clinical trials. Presented
within this article are the key issues identified by the task force during its initial year of deliberation. These include
the precise purpose for a clinical assessment tool, the clinical dimensions to be measured in a multidimensional outcome
measure, desirable attributes of an optimal clinical outcome measure, the complexities of multidimensional outcome
measures, the relative merits of categorical clinical ratings and quantitative functional assessments, and a number of
other important design issues that relate to the use of a multidimensional outcome measure. An action plan for analysis
of existing data is summarized, as are the plans for more detailed recommendations from the task force.
Rudick R, Antel J, Confavreux C, Cutter G, Ellison G, Fischer J, Lublin F, Miller A, Petkau J,
Rao S, Reingold S, Syndulko K, Thompson A, Wallenberg J, Weinshenker B, Willoughby E.
Clinical outcomes assessment in multiple sclerosis. Ann Neurol 1996;40:469-479
Assessing the impact of experimental intervention for
multiple sclerosis (MS) requires clinical outcome assessment tools [I], but precise clinical measurement in MS
patients is difficult for many reasons. The clinical manifestations vary widely in different patients, and vary
within a given patient over time. Furthermore, the clinical course is not usually characterized by steady worsening, but rather by variable episodes of clinical worsening followed by improvement, by long periods of
stability, o r by phases of steadily progressive clinical deterioration. This is complicated by the fact that neurological impairment and disability are inherently difficult
to quantify. Thus, precise and universally accepted assessment tools for use in MS clinical trials have been
difficult to develop.
In response to these difficulties, the National Multiple Sclerosis Society (NMSS) sponsored an international workshop titled “Outcomes Assessment in Multiple Sclerosis Clinical Trials: A Critical Analysis” in
Charleston, South Carolina, in February 1994. Among
other deliberations, participants at the workshop identified desirable attributes for clinical measurements: en-
dorsed a multidimensional assessment measure that
contains the multiple, relatively independent clinical
dimensions of MS, including cognitive function; and
agreed that no existing clinical scale was optimal [2].
The report from the Charleston meeting [2] stated
From the * Mellen Center, Cleveland Clinic Foundation, Cleveland,
OH; ?Montreal Neurological Institute, Montreal, Quebec, Canada;
$Hopital De L-Antiquaille, Lyon, France; $AMC Cancer Institute,
Denver, CO; ?University of California at Los Angeles Medical Center, Los Angeles, C1z; **JeffersonMedical College, Philadelphia, PA;
??Maimonides Medical Center, Brooklyn, NY; $$University of
British Columbia, Vancouver, British Columbia, Canada; SSMedical College of Wisconsin, Milwaukee, WI; SSNational Multiple
Sclerosis Society, New York, NY; ***VA Medical Center West
Los Angeles, Los Angeles, CA; TttInstitute of Neurology, Queen
Square, London, United Kingdom; $$$Bedex Laboratories, k c h mond, CA; $$$Mayo Clinic, Rochester, MN; and SSSAukland
Hospital, Auckland, New Zealand. The authors constitute the Clinical Outcomes Assessment Task Force, under the Advisory Committee on Clinical Trials of New Agents in Multiple Sclerosis of the
United States National Multiple Sclerosis Society.
There is a clear need for development of new assessment
systems, probably based upon the best aspects of the EDSS
scales [Kurtzke Expanded Disability Status Scale]. Any new
system must be multidimensional and quantitative. Preferentially, its scoring should be automated to speed the process
and to improve consistency from assessment to assessment,
between raters and among centers. It should have adequate
evaluation of cognition for which there are many validated,
though not currently practical, systems.
The Multiple Sclerosis Clinical Outcomes Assessment
Task Force (herein referred to as the Task Force) was
convened by the NMSS Advisory Committee on Clinical Trials of New Agents in Multiple Sclerosis as a
direct result of the Charleston workshop, to develop
Received Mar 13, 1996. Accepted for publication Mar 13, 1996.
Address correspondence to Dr Richard Rudick, Mellen Center,
Cleveland Clinic Foundation, Cleveland, O H .
Copyright 0 1996 by the American Neurological Association 469
recommendations for optimal clinic,al assessment measures for use in future MS clinical trials.
The Task Force consists of 16 members representing
five countries, with expertise in neurology, psychology,
biostatistics, epidemiology, and drug development. The
Task Force will develop recommendations for endorsement by the NMSS Advisory Committee on Clinical
Trials. The recommendations will be then forwarded
to the Medical Advisory Board of the NMSS for their
approval. Subsequently, these guidelines will be distributed as a resource for investigators and clinical trial
sponsors seeking optimal design strategies for MS clinical trials. The recommendations will also be forwarded
to the International Federation of Multiple Sclerosis
Societies for their consideration and further dissemination. A similar process resulted in guidelines for clinical
trials in motor neuron disease [3]. The purpose of this
article is to provide a summary of the Task Force deliberations to date as background for its recommendations, which will follow.
a clinical outcome assessment tool for controlled clinical trials probably would not be optimal for classifying
individual patients by disease type, for routine clinical
care, for specialized purposes like testing symptomatic
therapies (e.g., drugs for bladder dysfunction), or for
economic or quality of life studies. These were considered important purposes for clinical outcome measures,
but the Task Force decided to focus on developing an
outcome measure for clinical trials focused on interventions designed to modify the disease course.
The Task Force agreed to focus on developing a
measure for disease progression, defined as sustained
neurological or neuropsychological deterioration with
resulting disability. We recognized that an outcome assessment measure tailored to this purpose may not be
optimal for assessing the characteristics of relapses. Assessment measures for detecting and grading relapses
may comprise a subsequent goal of the Task Force.
Goal of the Task Force
Sensitivity to disease progression, also called sensitivity
or responsiveness [4, 51, was considered a key attribute
for a clinical assessment tool used in MS clinical trials.
If the clinical measure does not change during the
course of the trial in the control group, it cannot be
useful as an outcome measure because it will fail to
demonstrate a difference in the active treatment arm,
unless there is marked improvement in the treated
group. The need for adequately sensitive or responsive
measures is considered one of the greatest challenges,
because clinical trials are currently conducted over a 2to 3-year time frame while populations of MS patients
experience clear clinical deterioration over time frames
longer than 10 years.
The required sample size for a clinical trial is affected
not only by the trial duration, but also by the responsiveness of the clinical outcome measure. Currently, using a placebo control group and traditional clinical
outcome measures such as the EDSS, it has been possible to demonstrate statistically significant therapeutic
effects with approximately 150 patients per treatment
arm and a study duration of 2 to 3 years. As trials
become more complex, with multiple treatment arms,
sample sizes will have to increase significantly, adding
to the complexity and cost of studies. More sensitive
outcome measures could reduce the required sample
size or length of study, thereby conserving resources.
The need for increased outcome measure sensitivity
also dramatically escalates with partially effective therapies, as illustrated by the following. Assume one wishes
to determine the effect of an intervention compared to
a placebo. Further, assume that 40% of the placebo
group experiences a significant worsening in 3 years
compared to only 24% of the active treatment group.
Using a two-tailed test of significance with a = 0.05
2. “. . . the outcome measure must be useful for
demonstrating clinical change due to MS.
”
At its initial meeting (Chicago, October 14-15, 1994)
the Task Force agreed that the purpose for any clinical
outcome assessment tool must be (clear in advance of
developing the outcome measure. The group concluded that in its activity, it would strive to recommend a clinical outcome assessment tool for future MS
clinical trials. The purpose of this clinical outcome assessment tool will be to reflect the impact of an intervention on the progression of disease. Therefore, the
outcome measure must be useful for demonstrating
clinical change due to MS. The outcome measure will
be multidimensional to reflect the principal ways MS
affects an individual, have high reliability and validity,
be sensitive to change over short time intervuls to permit
demonstration of a therapeutic effect, and must be
both practical and cost-effective. [Italics are authors’ emphasis.]
Rationale for Task Force Goal
The Task Force goal was adopted after considerable
discussion regarding the component phrases, those italicized in the previous quote. In the sections that follow,
details explaining the Task Force goal are provided.
1. “The Task Force will recommend a clinical
outcome assessment tool for fiture M S clinical trials.
The puTose of this clinicul outcome ussessment tool
will be to reflect the impact of an intervention on
the progression o f disease. )’
The most pressing need recognized by the Task Force
was for an assessment tool to facilitate progress in developing effective MS disease therapies. The Task
Force recognized that no individual assessment tool
would be optimal for all clinical purposes. For example,
470 Annals of Neurology
Vol 40
No 3
September 1996
and 1 - p = 0.80 (power = go%), the study would
require 132 subjects per group, or a total of 264 subjects. Once a treatment that accomplishes this goal
(e.g., clinical worsening is reduced from 40% to 24%)
is identified, a trial is designed to test an alternative
therapy against the partially effective new treatment.
The study is designed with the same assumptions, only
the new treatment is required to reduce the worsening
by 40% from the previous partially effective result of
24%. The new study would require 260 patients per
group or a total of 520 patients, which represents a
doubling of the sample size. This doubling of the sample size would require either many more clinical centers
or longer duration of enrollment to answer the question of treatment effectiveness. Thus, as partially effective therapies are identified, the required sample size
or length of follow-up increases in subsequent trials
using the same outcome measure. This example illustrates a problem that has already arisen with the advent
of partially effective interventions [6-81. Assessment
measures that change more quickly (i.e., are more sensitive) might allow smaller sample sizes or shorter studies for subsequent clinical trials attempting to improve
on earlier results.
3. “The outcome measure will be multidimensional
to reflect the princ$al ways MS affects an
individual. . . .
Clinical heterogeneity typifies MS patient populations.
Individual MS patients manifest impairments in visual,
”
sensory, pyramidal, cerebellar, brainstem, and forebrain
association pathways with consequent functional problems with vision, ambulation, sensory function, leg and
arm weakness and coordination, bowel and bladder
control, and cognitive function. This clinical heterogeneity prompted earlier MS investigators to propose
multidimensional outcome measures [9]. The Task
Force endorsed the approach of including the main
clinical dimensions of MS in a primary multidimensional outcome measure, although it is recognized that
not every clinical manifestation could or should be included in a clinical outcome measure. The choice,
then, is to determine which dimensions to include.
The Task Force reviewed two separate methods for
determining the principal clinical dimensions of MS
that should be measured. The first method, factor analysis, is a statistical method that groups variables or tests
by their relatedness to other variables or tests [lo]. The
second method involves the written and verbal reports
of patients and professionals experienced with the disease [1 I]. Given the sources of data that are available
in well-characterized MS populations, both methods
converge in identifying similar clinical dimensions.
Factor analysis has been applied to a number of data
sets from MS clinical trials (12, 131 that include subjects with relapsing remitting as well as chronic pro-
gressive MS. Factors identified by these analyses are
remarkably consistent across data sets. The following
dimensions of MS have been identified by this method:
(1) leg dysfunction; ( 2 ) arm dysfunction; (3) sensory
dysfunction (superficial touch, position sense, and
possibly vibration threshold); ( 4 ) visual dysfunction;
(5) mental or cognitive dysfunction; and (6) bowel, bladder, and sexual dysfunction. The analyses also demonstrated that these six dimensions are highly correlated
with neuropsychological testing, elements from the standard neurological examination, the Kuttzke EDSS and
functional system scores (FSSs), quantitative motor testing, and patient self-report measures. For example, the
pyramidal FSS from the EDSS was most closely associated with the leg dysfunction dimension, and the cerebellar and brainstem FSSs were most closely associated
with the arm dysfunction dimension. Clinicians on the
Task Force endorsed the validity of these six clinical
dimensions identified by factor analyses. Specifically,
neurologist members of the Task Force who see large
numbers of MS patients in their practices generally concurred that the six areas were reasonable clinical dimensions on which to focus measurements. Additionally,
the neurologists on the Task Force recommended that
gait and mobility testing be included as a separate factor
from leg function.
The Charleston meeting participants had endorsed
the inclusion of neuropsychological assessment as a
component of the clinical outcome measure. The Task
Force reviewed existing studies of cognitive function in
MS patients and agreed that cognitive assessments can
be practical to administer, are sensitive to change in
MS patients, and correlate with changes in a relevant
nonclinical measure-cranial
magnetic resonance imaging (MRI)-in properly controlled trials. A community-based sample of MS patients tested longitudinally
indicated that some individuals experience progressive
neuropsychological impairment over a 3-year time
frame and that this had demonstrated criterion validity;
that is, worsening on neuropsychological tests was correlated with increasing MEU forebrain disease burden
[ 141. Furthermore, analysis from recent clinical trials
demonstrated treatment effects on measures of complex
attention [ 151. The Task Force therefore concluded
that tests of neuropsychological functioning should be
considered for inclusion in a clinical outcome measure.
While the Task Force supports the use of a clinical
outcome measure that will optimally assess the abovenoted principal MS clinical dimensions, it has not
made a final determination about whether or nor to
include measures for all six dimensions or specifically
which measurement tools should be used for each dimension. This will depend on the availability of simple
and efficient methodology for reliably quantifying the
dimension (e.g., this may be very difficult for bowel,
bladder, and sexual dysfunction, and remains to be
Special Report: Rudick et al: Clinical Outcomes Assessment in MS
471
demonstrated for neuropsychological dysfunction), the
relationship between change among the variables (e.g.,
if two variables always change together, including both
is redundant), the sensitivity to detect change (e.g., if
a particular variable does not change appreciably in the
time course of a controlled clinical trial, it will not be
useful as part of a multivariate or composite outcome
measure), and the relative frequency of occurrence of
that dimension in a particular sample of MS patients
(e.g., if only a small subset of patients can be expected
to show a particular sign or performance change, then
it may not be useful or cost-effective in detecting statistically significant change in the whole sample). Coming
to a consensus about measures for i:he relevant clinical
dimensions is an ongoing Task Force activity.
Table 1. Desirable Attributes of Clinical Outcome Measurer”
for MS Trials
Explanation
Performance attributesh
Level of measurement‘
Reliability
Sensitivity
Validity
4. “The outcome measure will . . . have high
reliability and validig, be sensitive change over
short time intervals to permit demonstration of a
therapeutic effect, and must be both practical and
cost-effective.
Desirable attributes for MS clinical outcome measures
160
Practical advantages
Easy to administer
”
were discussed at the Charleston consensus workshop
[ 2 ] .These attributes (Table 1) significantly influence
the effectiveness of outcome measures when applied in
the clinical setting [ 161.
Measures are used to order
individual scores within scales [17]. Measures can be
grouped within nominal, ordinal interval, or ratio
scales. Nominal scales group individual cases without
rational quantitative relationships among the categories
(e.g., males or females, African Americans or Whites).
In ordinal scales, or so-called ordered classifications,
scores represent groupings of some underlying measurement scale. The Kurtzke EDSS is an example of
an ordinal scale. Ordinal scales are used under two different circumstances. First, the ordinal scale can represent a grouping of scores derived using a continuous
scale (e.g., 75-100% of normal function is grouped as
normal; 50-75%, as minimal impairment; 25-50%,
as moderate; and 0-25%, as severe). Second, the ordinal scale can be used when the phenomenon in question cannot be measured using a continuous scale. In
that setting, the ordered classification represents an attempt to approximate the continuous scale by a cruder
scale that is the best one can do at rhe time. The quantitative distance between steps on ordinal scales in this
circumstance may be unknown, and it is generally inappropriate to use arithmetic oper.itions and parametric statistical tests to analyze change on ordinal scales.
In interval or continuous scales, scores are ordered with
an indication of how far apart the objects are from one
another, and for ratio scales scores are also assigned
with respect to the distance from an absolute zero. ExI EVEL OF MEASURFMENT
472 Annals of Neurology Vol 40
No 3 September 1996
Acceptable to patients
and health care
professionals
Resource efficient
The score should be quantitative to the extent possible,
and the distance between
points on the scale should
be known.
The score should have a high
intrarater and interrater reliability, or for self-report measures should have high testretest reproducibility.
The measure should be sensitive to clinical change over a
relatively short time interval.
The clinical outcome measure
should have demonstrable validity as discussed below.
The test measure should be
easy and quick to administer.
The measurement technique
should be consistent with
comfort, safety, and compliance.
The test measure should conserve time and resources.
‘A “measure” is a set of rules designed to assign numbers to relevant
phenomena (e.g., leg or visual function). In MS, demographic measures (e.g., age, gender) are straightforward and do not require complex rules; “disease measures” are used to measure constructs (our
hypotheses about the ways the MS disease process affects the individual, e.g., sensory dysfunction, ataxia). Disease measures are more
complicated and require a more elaborate set of rules.
bAn attribute is a characteristic of a measure.
‘Scores from clinical measures are used to place an individual along
a scale. Scales can be nominal, ordinal, or interval scales, which
have varying characteristics, as discussed in the text.
amples of interval or continuous scales are timed tests
of neurological function [ 181. Internal scales offer the
potential advantage that arithmetic operations, such as
taking differences between the end and beginning of
the trial, are meaningful. This makes statistical analysis
of change straightforward. The Task Force recognized
the advantages of interval scales, when they are available to measure the dimensions of interest.
KELIABILITY. This refers to the reproducibility of an
outcome measure. The usefulness of an outcome measure is directly related to its reliability, as change over
time from disease progression or improvement can be
obscured by variability derived from the outcome measure itself. Standard methods can be used to assess reliability, including repeated measurements made by the
same rater in the same session or over short time intervals such as successive days (intrarater or test-retest reli-
ability), and repeated measurements made on the same
subject by different raters (interrater reliability),
Validity is defined as measuring what one
intends to measure. Various types of validity have been
defined and discussed in detail elsewhere (e.g., see [19,
201 for particularly illuminating discussions). Criterion
validity refers to cross-validation of the outcome measure with another relevant measure, such as MRI. Predictive validity refers to the ability of a measure to
predict future clinical status. For example, significant
change on a quantitative test of upper extremity function observed during a 12-month period may not be
of obvious clinical significance, but may be shown to
have predictive validity by demonstrating a relationship
between short-term change and inability to use the arm
for feeding 5 years later. In this context, the outcome
measure (e.g., quantitative assessment of upper extremity function) may predict the subsequent behavior on a
criterion variable (e.g., ability to dress or feed oneself).
Predictive validity is particularly important when making short-term measures of a slow chronic process. The
Task Force recommends demonstrating the predictive
validity for outcome measures when the clinical relevance of a short-term change is not obvious [I].
VALIDITY.
Costs relate to personnel,
equipment, space, and time requirements. Optimally,
administration time for the clinical outcome assessment
measures should be brief. The clinical assessment measure should also be acceptable to both neurologists and
patients. Testing should be comfortable and safe for
the patient. Any instrumentation must be highly reliable, easy for training and administration, and usable
over a wide range of patient disability status [21].
P u c m x L ADVANTAGES.
Complexities and Challenges in Achieving
the Goal
Several challenges and complexities in improving MS
outcome measures have been considered by the Task
Force. These include the difficulty in precisely quantifying neurological function; the need to evaluate different existing outcome measures for their potential value
in a new outcome assessment measure; and the complexities of a multivariate outcome measure, which is
required to simultaneously measure multiple clinical
dimensions.
1. Quantifiing Neurological Function
The World Health Organization [22] distinguished
impairment from disability and handicap. According
to this classification, impairment is caused by the underlying disease process and results in abnormalities evident on the neurological examination. Functional consequences of these impairments resulting in problems
with activities of daily living are termed disabilities.
These can be quantified by standardized timed tests of
neurological function. The vocational, social, or role
limitation resulting from the interaction between disability and the environment are termed handicaps,
which can be measured by quality of life methodologies.
The Task Force advocated measuring impairment
with categorical clinical ratings, and disability using
quantitative functional assessments. Quality of life
scales, while considered extremely important, were not
thought appropriate to directly quantify the neurological effects of the disease process. The relative merits of
categorical clinical ratings and timed functional assessment in an MS clinical outcome measure are unclear.
It was recognized, however, that timed functional assessments may offer significant advantages over clinical
rating scales because function can be measured reliably
and expressed on an interval scale. In contrast, the neurological examination is commonly expressed as an ordinal scale with nonlinear and indistinct boundaries between steps [23, 241.
2. Comparing Alternative Assessment Tools
There is a clear need to compare reliability, sensitivity,
predictive validity, and cost-effectiveness of quantitative tests of neurological function with available clinical
ratings in MS patients to guide development of an optimal clinical outcome measure. However, comparison
of measures that use different metrics is difficult. A
variety of statistical procedures have been proposed [4,
25-32], but only a few have been applied to data from
MS patients. These techniques can be used to assess
relative sensitivity to disease progression (change over
time in placebo-treated patients) and to treatment effect (differential change over time related to treatment).
One of the first methods applied in comparative
assessment of MS measures was signal-to-noise ratio
(SNR) analysis [12, 331. The SNR for linear change
is a ratio of the standard deviation for the linear orthogonal contrast (from a repeated-measures analysis of
variance) of a measure across all time points to the
average standard deviation for third-order and higher
orthogonal contrasts. It provides a quantitative index of
how strongly the change over time for a given measure
approximates a linear function and how steep the slope
is. The higher the linear SNR, the steeper the slope
and the better the fit to a straight line. The expectation
is that a good candidate assessment measure should
have a SNR higher than 2.0. Syndulko and colleagues
[33] showed that quantitative functional assessments
had favorable SNRs compared with clinical ratings of
neurological impairment in the placebo group from a
multicenter cyclosporine clinical trial.
A second candidate statistical procedure is effect size
[30, 34, 351. The value of effect size is to provide an
absolute scale along which to rank sensitivity of differ-
Special Report: Rudick et al: Clinical Outcomes Assessment in MS 473
ent outcome assessment measures TO disease progression or treatment effects using data from clinical trials.
An effect size is a standardized estirnate of the magnitude of a statistically determined experimental effect,
such as change over time in a group or the difference
between two groups [30].The effect size provides a
standardized unit of measurement for comparing the
sizes of changes for different outcome measures within
a study or between studies. It is used in addition to
the statistical p value to help interpret and compare
the meaningfulness of the changes found in a study.
It is also used to calculate the sample size required for a
proposed study to show statistically significant changes
between or within groups. Cohen [35] presented a
wide variety of effect size measures, their use for sample
size determinations, and their interpretation or meaningfulness. By using an effect size measure calculated
from the results of a repeated-measures analysis of variance, called the f index by Cohen, quantitative functional assessments in the multicenter cyclosporine clinical trial were found to have larger effect sizes than were
categorical clinical ratings [33].Confirmation of this
finding would mean that smaller sample sizes would be
required in clinical trials using quantitative functional
assessments as the primary outcome. assessment as opposed to clinical rating scales.
3. Complexities of a Multivariate Outcome Measure
In a multidimensional outcome measure, the score reflects more than one clinical dimension. At least in
the lower part of the range, the IZDSS represents a
multidimensional outcome measure that uses the neurological examination to make clinical ratings of the
different dimensions of MS (e.g., ithe functional systems), which are then combined into a single rating
[36], Such derived measures, often called composites,
have been used widely in medicine to characterize complex clinical phenomena [37].Roberts [38] provided a
succinct discussion of the advantages and disadvantages
of such composite measures.
A multivariate outcome measure, on the other hand,
is a collection of individual component measures, each
grading a particular aspect of the disease (e.g., ambulation, arm function, vision, cognitive function, bladder
function, and sensory function) and each retaining its
identity as an individual componenl . Each component
could itself be a composite measure lbased on a number
of measures of that same clinical dimension (e.g., a
“cognitive” score could represent the sum of three individual test scores). If it is not clear how the components corresponding to the different dimensions should
be combined into a composite outcome measure, then
statistical approaches are required for dealing with such
a multivariate outcome.
Dealing with a multivariate outcome entails numerous statistical complexities that were addressed by a
474 Annals of Neurology Vol 40 No 3 September 1996
member of the Task Force [39]. Suppose there are k
such dimensions with corresponding component measures that are continuous variables. Assume that the
principal parameter of interest is change (i.e., the difference between the final and baseline visits) and that
a treatment arm is to be compared with a placebo arm.
Two quite different simple statistical approaches can
then be described.
With the most common approach, the component
for each dimension is analyzed separately. The assessment of the treatment effect for each dimension is
based on the z score resulting from the difference between the mean change scores on the corresponding
component measure in the treated and placebo groups.
But the level of type I error for the comparison on
each dimension is adjusted for the number of dimensions, from a to a l k (Bonferroni adjustment), to ensure that the overall type I error for all k comparisons
is no more than the target level of a. The main difficulty with this approach is the need to increase the
sample size to achieve the more conservative alk significance level at a given level of power and the fact
that the overall type I error will be somewhat less than
the target value of a, thereby resulting in less overall
power than might otherwise be possible. Consider the
example provided earlier for a comparison that reduces
the worsening from 40% in the placebo group to 24%
in the intervention group. If we used measures for six
clinical dimensions of MS, we would then use a revised
type I error of 0.05/6 = 0.008. The effect of this lowered a = 0.008 corrected for the multiple comparisons
is to increase the required sample size from 132 to 205,
an increase of about 55%.
An alternative simple approach (based on Hotelling’s
T2 statistic) deals with the components corresponding
to all dimensions simultaneously to yield an overall
assessment of the treatment effect. For uncorrelated
components, this assessment is based on the sum of
the squares of the z scores resulting from the differences between the mean change scores on the individual component measures in the treated and placebo
groups. This approach can be viewed as one method of
combining the components of a multivariate outcome
measure into a composite outcome measure (the sum
of the squares of the zscores), where the composite is
constructed on a purely statistical basis. Because the
assessment is based on the squares of the z scores, this
can be described as an omnibus comparison of treatment and placebo, in that the analysis would indicate
there is a difference between treatment and placebo,
but would not indicate the direction of the difference
or on which dimensions change occurs. The individual
z scores would have to be inspected to determine the
behavior of each component measure, and the direction of change. With this approach, an overall significant effect could be obtained in the absence of signifi-
cant effects on any of the individual dimensions, and
similarly no differences may be seen overall, even when
there is a significant change in one dimension.
The design implications of this second approach relate primarily to power and sample sizes. The effect of
including additional measures using the second approach can be illustrated as follows. If a single measure
were to show a treatment effect ([mean change score on
treatment - mean change score on placebo] /standard
deviation of change score) of l/2, then with a two-tailed
test of significance with a = 0.05, a sample size of
100 patients per group would result in a power of
94%. Adding additional uncorrelated components that
showed no treatment effect would result in significantly
reduced power, or significantly larger sample sizes to
maintain the same statistical power. For example, the
addition of four uncorrelated component measures that
showed no treatment effect would reduce the power
from 94% to 79%, or increase the sample size required
to maintain the power of 94% from 100 to 153 per
group. This illustrates the danger of including dimensions that do not show a treatment effect when this
alternative approach for a multivariate outcome measure is used. In contrast, the addition of uncorrelated
components that do show treatment effects results in
improved power on reduced sample sizes required for
the same statistical power. The overall conclusion from
this analysis is that there is significant disadvantage to
including component measures that do not show a
treatment effect on change over time in a multivariate
outcome measure, but considerable benefit in including
multiple independent component measures that are
sensitive to change.
Petkau [39] provided a more detailed discussion of
these complexities, including comparisons with other
approaches to combining the component measures of
a multivariate outcome measure into a composite outcome measure [40, 411. In addition, Cutter (personal
communication, 1995) considered the effect of the relationship between composite and component change
by computer simulations. These studies confirmed that
the sample size requirement or power of the clinical
trial is directly influenced by correlations between the
components in a multivariate outcome measure.
The implications of the complexities of a multivariate outcome measure for designing MS studies are
summarized as follows (Table 2): (1) There are both
risks and benefits in using a multivariate outcome measure for MS studies. In particular, caution should be
used to avoid including multiple dimensions that do
not change with treatment, as this makes the detection
of change more difficult. Caution should also be used
to avoid including multiple, highly correlated measures
because they add little new information about change
while increasing the total variability, again making the
detection of change more difficult. (2) All components
Table 2. Attributes of a Multivariate Clinical Outcome
Measure for MS Trials
Measure Attribute
Explanation
Multidimensional
The outcome measure is based
on components that measure
different key dimensions of
the disease.
The individual components of
the outcome measure change
in a significant proportion of
the population.
Change in the individual components is relatively independent from other components.
Available scores should allow
classification of all patients
and avoid ceiling effects.
Individual components
change over time
Components change independently
Applicable to range of
MS severity most often included in MS
trials
of a multidimensional outcome measure should have
optimal performance characteristics (e.g., they should
have high reliability, validity, and sensitivity [see Table
11). ( 3 ) The inclusion of various measures of the principal clinical dimensions should be based on both expert
opinion and careful empirical investigations in which
available data on candidate outcome assessments are
analyzed to determine their variability and sensitivity
to change over time.
How Should the MS Clinical Outcome
Measure Be Used?
It is necessary not only to identify an optimal outcome
measure, but also to define how it should be used, and
to address its impact on important trial design issues
[42].For example, one could simply look at the difference in change scores between treatment groups on
the outcome measure or one could define significant
change (e.g., a certain amount of worsening or improvement) and compare the proportions in the treatment arms who change by this amount. Alternatively,
one could conduct a time analysis (e.g., time to an
event, such as treatment failure). The optimal approach
will be determined by characteristics of the outcome
measure, the specific goal of the clinical trial, and a
number of statistical factors. Questions that need to be
addressed are discussed below.
I . Should study entry be restricted to a range 0fperf.rmanee on the outcome measure? There have been attempts to restrict entry into MS clinical trials to improve subject homogeneity, in order to increase the
sensitivity for observing a therapeutic effect. Entry into
trials has typically been restricted to a subpopulation
based on the outcome measure to be used in the trial
Special Report: Rudick et al: Clinical Outcomes Assessment in MS
475
(e.g., 2 2 exacerbations in the past 2 years, EDSS of
1.0-3.5, etc). It will obviously be necessary to restrict
entry to trial subjects who can be adequately evaluated
by a particular outcome measure, and it seems unlikely
that a single outcome measure will be optimal for the
entire disease severity spectrum. Whether it will be appropriate to restrict entry to a limited subset based on
performance on a particular outcorne measure is unclear at present.
2. Is a “run-in”period necessary? MS patients frequently remain clinically stable for long periods of
time, so an observation phase without active treatment,
termed a run-in period, has been used to select patients
with active disease for inclusion in 1-he trial. Generally
speaking, short run-in periods are likely to be noninformative in this regard due to the slow pace of clinical
change, but potential advantages include allowing the
trial participants time to become comfortable with the
study personnel and the measurement techniques, to
identify practice effects, and to minimize their effects.
Disadvantages of a run-in period include the need for
additional resources.
Additionally, the course of MS is notoriously variable, and there is no predictable relationship between
observed clinical change during a run-in period and
subsequent clinical change during the treatment phase
[43].A common observation has been that subsets of
patients with very active disease during observation
have much less active disease during the treatment trial.
One explanation for this observation is the phenomenon known as regression toward the mean. This occurs
when groups are selected on the basis of their extreme
performance on a selection measure (e.g., selecting MS
patients with high relapse rates prior to entering a
trial). Because only those patients who are above the
eligibility level are entered into the trial and followed
for change, there is a tendency for the subsequent mean
levels to be lower. This results because of the natural
variability in the course of disease. Therefore, relapse
rates in some of the patients entered into the trial regress back to lower levels. The averaging of those more
representative values with values for those who continue to express high relapse rates lowers the overall
mean at follow-up because patients, who would have
balanced the group had the entire population been represented were excluded from the study because they
failed entrance screening. Thus, such selection results
in an artificial change in the outcome measure from
baseline to follow-up. The same phenomenon applies
to all clinical outcome measures.
Because of the slow pace of clinical change and the
phenomenon of regression to the mean, run-in periods
should be reserved for familiarizing subjects with the
test procedures and allowing subjects to reach stable
baseline levels on the outcome measures.
476 Annals of Neurology
Vol 40
N o 3 September 1996
3. Should patients be stratzfed by clinical course? MS
clinical trials have commonly restricted entry to particular types of disease based on their clinical course.
However, it may not make clinical sense to distinguish
between patients with relapsing remitting MS and
those with secondary progressive MS. These NVQ types
of MS are probably different stages of the same disease
and so many simply represent different durations and
severities of the disease. Furthermore, classification of
subjects into one or the other category is in many cases
ambiguous. Where an outcome measure is particularly
sensitive to disease change in one subtype versus another, restricted enrollment or stratification is important. O n the other hand, there is evidence that primary
progressive MS may be pathologically different from
secondary progressive MS, in that there is less brain
inflammation and gadolinium enhancement demonstrated by brain MRI [44].Therefore, it would be rational to conduct separate clinical trials for patients
with primary progressive MS or stratify by this in a
combined trial when the new treatment is of plausible
benefit to both groups.
4. How frequently are measurements needed? There
may be a need for frequent measurements during short
time periods (e.g., when determining a “slope” using
a very sensitive outcome measure). However, making
measures too frequently may introduce noise in some
circumstances and may actually decrease power for
showing an effect for change over time. The effect size
(discussed already) can be used to evaluate outcome
measures from completed clinical trials in simulated
trials of variable duration and sampling intervals to
help answer this question. For example, in a 2-year
clinical trial with evaluation visits every 3 months, the
data from the trial can be used to create simulated trial
durations of 6 months and 1 year in addition to the 2year trial to compare sensitivity to change of candidate
outcome assessments over the shorter time intervals.
Similarly, examinations every 6 months or 1 year can
be used to evaluate the effects of longer interexamination intervals on sensitivity to change.
5. How does the outcome measure influence dropouts
in clinical trials? Dropouts remain a problem in MS
clinical trials. Consequently, it is necessary to include
a plan to handle the impact of dropouts when initiating an MS clinical trial. It may not be adequate to
simply inflate the sample size calculation to compensate
for the dropout rate. Inflating the sample size and ignoring the dropouts makes an assumption called noninformative censoring, which means that disease progression in the dropouts behaves in the same manner as
in the participants who continue to be followed. In
both the cyclosporine study [I31 and the interferon
beta-1 b (Betaseron) study [45],disease progression in
dropouts appeared to be greater than that in complet-
ers, however, so the assumption of noninformative censoring is not always met. The “intent to treat” analysis,
which is standard practice in clinical trials, forces the
inclusion of dropouts into efficacy analyses. If the disease behaves differently in the dropouts from the study
completers, then this has the potential for obscuring
treatment effects and reducing the power of the experiment, particularly when disease progression in the
dropouts is different in the active and control arms of
the study. Insensitive clinical outcome measures can
contribute to this problem, because trial participants
may perceive that they are worse and withdraw from
the study before change is detected by an insensitive
outcome measure. Innovative approaches to handling
dropouts will be required. Allowing clinical trial participants to pursue alternative treatments when they become “treatment failures” and employing more sensitive outcome measures may be the best approach to
this problem. New techniques aimed at longitudinal
data analyses do enable the experience of the dropouts
to be included, but outcome measures that identify
poor responders early may be more helpful than the
usual assumptions necessary for dealing with dropouts.
6 Should the same outcome assessment measures be
used to detect worsening and improvement?Relatively few
clinical trials have addressed the hypothesis that a given
therapy produces improvement in MS-related disability, as opposed to slowing or preventing deterioration.
Given the tendency for MS-related disability to wax
and wane in severity with fatigue and change in body
temperature, similar difficulties are inherent in detecting significant improvement as in detecting worsening. Mean change in a composite score will be influenced heavily by the “noise” of minor fluctuations in
composite disability scores. Noseworthy and colleagues
[46],in a protocol directly assessing the ability of intravenous immunoglobulin (IVIg) to produce improvement in recently acquired but apparently fixed MSrelated weakness, used quantitative isometric strength
measurements of “targeted” muscle groups. As the
mechanisms underlying neurological improvement (remyelination, spreading of excitatory sodium channels)
are likely different from those underlying neurological
deterioration (conduction block, demyelination, axonal
degeneration), improvement and worsening may not
be measurable as a continuum. Strict methodology
would require that the frequency of worsening should
be analyzed without regard to whether apparent improvement is seen on the same composite measure,
when the hypothesis under study is whether a given
agent can prevent progression of MS. There is insufficient experience at this time to determine whether the
same measurements or composites will be adequate to
assess improvement; furthermore, there is neither natural history experience nor experience from control
groups in relevant clinical trials to address this question.
Conclusions and Plans
1. Current assessments in MS patients are not optimally sensitive and precise to detect changes in
disease progression for trial durations less than 3
years. This results in large sample sizes or long
study durations, or both. This problem will dramatically escalate with partially effective therapy,
assuming that future studies incorporate active
treatment comparison groups. Subjects in the
comparative group can be expected to worsen
more slowly than a placebo-treated group in future
trials, requiring more sensitive outcome measures,
larger sample sizes, or longer durations.
2. Newer outcome measures and new approaches will
be necessary in the future to accelerate progress in
developing effective therapies. Change over short
time intervals on new outcome measures may not
be of obvious clinical significance. It will be important to demonstrate the predictive validity of
new or modified outcome measures (i.e., change
on the outcome measure must be linked to subsequent clinically significant change).
3 . The clinical dimensions that should be considered
for new MS clinical assessment measures include
tests of leg function, ambulation, and mobility;
arm function; and cognitive function. The arguments for a role of visual, sensory, and bowel and
bladder testing are less compelling.
4. Optimal clinical assessment measures for clinical
trials may not be optimal for evaluating patients
during clinical practice, for clinical decision making, or for classifying disease type.
5. Quantitative functional assessment of neurological
function may be a useful alternative to clinical ratings derived from the neurological examination.
Quantitative functional assessments may offer advantages in terms of reliability, continuous rather
than ordinal scales, and increased sensitivity to
change over time, but potential disadvantages include unknown predictive validity, neurologist and
patient acceptance, cost-effectiveness, and practicality, which remain to be demonstrated.
6. A methodology to compare different outcome assessment measures for their utility in clinical trials
is needed. Candidate measures include SNRs and
effect size. Methods for comparing different outcome assessment measures may not be limited to
these two methods; alternatives need to be explored and the optimal method(s) utilized.
7. Multivariate clinical outcome measures present
complexities and challenges. The use of a multivariate outcome measure may increase or decrease the
Special Report: Rudick et al: Clinical Outcomes Assessment in MS
477
power of an intervention trial, depending on
whether the intervention affects multiple measures
(increasing power), and how rnany measures not
affected by the treatment (decreasing power) are
included. The number of dimensions should be
limited, and analyses should be conducted to confirm that the measures have favorable performance
characteristics and change ovei time in untreated
or placebo-treated MS patients.
8. It will be necessary to develop flexible outcome
measures in order to meaningfully measure the
spectrum of disease severity. As individual patients
“bottom out” on measures appropriate for lowdisability patients, more appropriate measures of
the same clinical dimension would be substituted.
9. Analysis of existing data that have been collected
from MS patients participating in controlled clinical trials and natural history studies will guide the
Task Force in recommendations for optimal clinical assessment measures. In this regard, the Task
Force developed and initiated a plan to evaluare
data from completed clinical trials and natural
history studies. The goals for this project are to
analyze the behavior of placebo recipients and untreated MS patients using various clinical measures, to determine performance characteristics of
these measures. The outcome from this analysis
will be reconciled with the basic principles formulated in this position statement and used to formulate guidelines for optimal clinical outcome
measures. The principles described here will be
reconciled with the actual perfbrmance of standard
clinical rating scales (e.g., EDSS, neurologic rating
and quantitative tests of neurological
scale [47]),
function (e.g., validated, timed tests of physical
and cognitive performance).
10. It is anticipated that the Task Force will recommend criteria and specific measures that can be
considered for inclusion in subsequent controlled
clinical trials by investigators and sponsors. It will
initially be necessary to utilize the recommended
assessment measures concurrently with standard
measures, so that the relative utility can be determined prospectively.
The work of the Task Force is supported by the US National Multiple Sclerosis Sociery wirh an unrestricted educational grant from
Berlex Laboratories.
The Task Force is grateful to Drs Theodore Munsat and John
Whitaker for their helpful suggestions about the manuscript.
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