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From pain intensity to a holistic composite measure for spinal cord stimulation outcomes

Journal Contribution - Journal Article

EditordDespite the beneficial effects of spinal cord stimulation
in reducing pain intensity,1 diminishing pain medication use,2
and improving return to work,3 the implantation of spinal
cord stimulators involves a high cost. Reimbursement for a
spinal cord stimulator implant is often conditional on a
successful trial period with country-related definitions to
determine success of such a trial with varying trial durations
(i.e. without a standard, worldwide definition of a successful
trial).4 Most reimbursement rules incorporate a 50% reduction
in pain intensity,5 whether or not combined with other
criteria, such as reduction in pain medication use, and at least
stable levels of daily activity. Moreover, guidelines for the
management of neuropathic pain and number needed to treat
have incorporated this threshold. The real meaning of a 50%
threshold of improvement has not been subjected to trials
that evaluate its validity in practical terms and its relationship
to related factors, including psychological improvement,
social adjustment, mood evaluation, and return to work.6
To avoid oversimplification of a person’s health status and
the complexity of chronic pain, a more holistic approach is
currently implemented in the field of chronic pain, and more
specifically for neuromodulation.7 Over the past 3 yr, this
vision has been operationalised by several key opinion leaders
under the form of composite measures. Composite measures
have the strength to combine information into a summary
measure for the treatment effect, especially when more than
one outcome is of interest.8 They combine two or more constructs into one overall measure, thereby providing a more
comprehensive assessment and presumably a more clinically
relevant measure of multiple domains compared with a single
measure of pain intensity reduction.9 The individual components of a standard composite measure are implicitly ascribed
a similar weight and should be reported as separate secondary
endpoints in a clinical trial.10 Specifically related to neuromodulation, four different research groups have effectively
created a composite measure to date, all developed on data
from multicentre studies in patients with persistent spinal
pain syndrome Type II (previously known as failed back surgery syndrome)11e15 (Table 1). To determine which variables
should be included in the composite measure, all groups relied
on statistical analysis to determine the variables that
explained most of the variance in the outcome measure. This
shift from pain intensity-driven responder-based definitions
towards standardised scales ensures a finer gradation of
assessment that is highly beneficial in relation to the
complexity of chronic pain and overcomes the often lower
statistical power of dichotomous responder-based outcome
measurements compared with continuous outcomes.9
In contrast to published initiatives with statistical approaches, another way of combining endpoints is through the
creation of multicomponent endpoints, in which numerous
pre-specified component outcomes are combined into a single
score with a weighted or unweighted underlying approach.10
Compared with composite measures, the components within
a multicomponent endpoint might not be clinically meaningful when analysed separately.10 For both composite endpoints
and multicomponent endpoints, weights can be assigned
through expert judgement (e.g. a Delphi panel process) or
through stated (realistic, hypothetical choice scenarios, e.g.
visual analogue scale) or revealed (real-life choice scenarios,
e.g. disability-adjusted life years) preference methods.10
Despite the innovative aspects of the composite measures
developed in the field of neuromodulation, most do not
incorporate a weighting system based on stakeholder opinions. Assigning weights based on both patient and physician
ratings would further refine the current definitions of composite measures in the field of neuromodulation.
Perceived capacity, as often evaluated with self-reported
questionnaires by the patient, and actual abilities of chronic
pain patients are two distinct yet complementary aspects to
evaluate a broader spectrum of health status.7 This does not
mean that self-reported measures can be replaced by more
objective tools, nor that objective measurements can be
replaced by self-reported measures. Both types of evaluations
provide complementary information to gain insight in the full
representation of the patient. Some of the more objective
outcome measures already explored in the field (e.g. heart rate
variability, skin conductance, quantitative sensory testing,
neuroimaging [attributable to the supraspinal mechanisms of
spinal cord stimulation]) hold the capacity to measure the effects of a pain management treatment. Nevertheless, validation studies are needed to confirm the performance of the
more objective outcome measures as markers of the success
of neuromodulation.
Ultimately, the goal would be to bring together a refined
definition of a holistic composite measure with appropriate
weights relevant to patients and physicians to measure ability
together with the output of a more objective measurement
tool to evaluate ability into one overall multi-component
endpoint for evaluating the effectiveness of neuromodulation. This new measure should be applicable in both
clinical practice and research settings, and perhaps even as a
holistic outcome evaluation for reimbursement criteria. Longitudinal follow-up with this multi-component endpoint
should be able to provide insights into long-term responsiveness to neuromodulation, predictors for habituation, and
eventually identification of factors that result in device
explant. We therefore propose a multi-component endpoint to
assess both perceived capacity and actual ability for holistic
evaluation of the success of neuromodulation.
Journal: British Journal of Anaesthesia
ISSN: 0007-0912
Issue: 2
Volume: 131
Pages: 43-48
Publication year:2023
Keywords:chronic pain management, composite measures, neuromodulation, objective markers, pain measurements, spinal cord stimulation