The ACTTION-American Pain Society Pain Taxonomy (AAPT): An evidence-based and multidimensional approach to classifying chronic pain conditions

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Abstract
Current approaches to classification of chronic pain conditions suffer from the absence of a systematically implemented and evidence-based taxonomy. Moreover, existing diagnostic approaches typically fail to incorporate available knowledge regarding the biopsychosocial mechanisms contributing to pain conditions. To address these gaps, the Analgesic, Anesthetic, and Addiction Clinical Trial Translations Innovations Opportunities and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration and the American Pain Society (APS) have joined together to develop an evidence-based chronic pain classification system called the ACTTION-APS Pain Taxonomy. This paper describes the outcome of an ACTTION-APS consensus meeting, at which experts agreed on a structure for this new taxonomy of chronic pain conditions. Several major issues around which discussion revolved are presented and summarized, and the structure of the taxonomy is presented. ACTTION-APS Pain Taxonomy will include the following dimensions: 1) core diagnostic criteria; 2) common features; 3) common medical comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors. In coming months, expert working groups will apply this taxonomy to clusters of chronic pain conditions, thereby developing a set of diagnostic criteria that have been consistently and systematically implemented across nearly all common chronic pain conditions. It is anticipated that the availability of this evidence-based and mechanistic approach to pain classification will be of substantial benefit to chronic pain research and treatment. The ACTTION-APS Pain Taxonomy is an evidence-based chronic pain classification system designed to classify chronic pain along the following dimensions: 1) core diagnostic criteria; 2) common features; 3) common medical comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors.
Focus Article
The ACTTION-American Pain Society Pain Taxonomy (AAPT):
An Evidence-Based and Multidimensional Approach to Classifying
Chronic Pain Conditions
Roger B. Fillingim,
*
Stephen Bruehl,
y
Robert H. Dworkin,
z
Samuel F. Dworkin,
x
John D. Loeser,
{
Dennis C. Turk,
ll
Eva Widerstrom-Noga,
#
Lesley Arnold,
**
Robert Bennett,
yy
Robert R. Edwards,
zz
Roy Freeman,
xx
Jennifer Gewandter,
{{
Sharon Hertz,
llll
Marc Hochberg,
##
Elliot Krane,
***
Patrick W. Mantyh,
yyy
John Markman,
zzz
Tuhina Neogi,
xxx
Richard Ohrbach,
{{{
Judith A. Paice,
llllll
Frank Porreca,
###
Bob A. Rappaport,
****
Shannon M. Smith,
yyyy
Thomas J. Smith,
zzzz
Mark D. Sullivan,
xxxx
G. Nicholas Verne,
{{{{
Ajay D. Wasan,
llllllll
and Ursula Wesselmann
####
*Pain Research and Intervention Center of Excellence, Gainesville, Florida.
y
Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, Tennessee.
z
Department of Neurology in the Center for Human Experimental Therapeutics; and Director, Analgesic, Anesthetic,
and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION), University of Rochester
School of Medicine and Dentistry, Rochester, New York.
x
Department of Psychiatry and Behavioral Sciences, School of Medicine, Department of Oral Medicine, School of
Dentistry, University of Washington, Seattle, Washington.
{
Department of Neurological Surgery, University of Washington, Seattle, Washington.
ll
Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, Washington.
#
Health Scientist VHA, University of Miami, Miller School of Medicine, Miami Project to Cure Paralysis, Miami, Florida.
**Department of Psychiatry and Behavioral Neuroscience, and Director, Women’s Health Research Program, University
of Cincinnati College of Medicine, Cincinnati, Ohio.
yy
Fibromyalgia Research Unit, Oregon Health & Science University, Portland, Oregon.
zz
Brigham & Women’s Hospital, Chestnut Hill, Massachusetts.
xx
Department of Neurology, Harvard Medical School, Cambridge, Massachusetts.
{{
Department of Anesthesiology, University of Rochester School of Medicine and Dentistry, Rochester, New York.
llll
Food and Drug Administration, Center for Drug Evaluation and Research, Silver Spring, Maryland.
##
Department of Medicine, Division of Rheumatology and Clinical Immunology, University of Maryland School of
Medicine, Baltimore, Maryland.
***Departments of Anesthesiology, Perioperative, and Pain Medicine, Pediatrics, Stanford University School of
Medicine, Stanford, California.
yyy
Department of Pharmacology, University of Arizona, Tucson, Arizona.
zzz
University of Rochester Medical Center, School of Medicine and Dentistry, Rochester, New York.
xxx
Clinical Epidemiology Unit, Boston, Massachusetts.
{{{
Department of Oral Diagnostic Sciences, University at Buffalo, Buffalo, New York.
The views expressed in this article are those of the authors, none of whom
has a financial conflict of interest related to the specific issues discussed in
this manuscript. All of the authors attended the consensus meeting on
which this article is based. In addition, the consensus meeting was at-
tended by employees of Pfizer, one of the companies that provided unre-
stricted grants to ACTTION to support its activities. However, these
individuals did not contribute to the content of this manuscript.
No official endorsement by the U.S. Food and Drug Administration (FDA)
or the pharmaceutical companies that have provided unrestricted grants
to support the activities of the Analgesic, Anesthetic, and Addiction Clin-
ical Trial Translations, Innovations, Opportunities, and Networks (ACT-
TION) public-private partnership with the FDA should be inferred . The
consensus meeting on which this article is based was funded by ACTTION,
which has received research grants or other revenue from the FDA,
various pharmaceutical compan ies, and other sources.
Address reprint requests to Roger B. Fillingim, PhD, University of Florida
College of Dentistry, UF Pain Research and Intervention Center of
Excellence Clinical and Translational Research Building (CTRB), Room
3216, 2004 Mowry Road, PO Box 100404, Gainesville, FL 32610-0404.
E-mail: rfilling@ufl.edu
1526-5900/$36.00
ª 2014 by the American Pain Society
http://dx.doi.org/10.1016/j.jpain.2014.01.004
241
The Journal of Pain, Vol 15, No 3 (March), 2014: pp 241-249
Available online at www.jpain.org and www.sciencedirect.com
llllll
Director, Cancer Pain Program, Division of Hematology-Oncology, Northwestern University, Feinberg School of
Medicine, Chicago, Illinois.
###
Department of Pharmacology, University of Arizona, Tucson, Arizona.
****Food and Drug Administration, Center for Drug Evaluation and Research, Silver Spring, Maryland.
yyyy
Department of Anesthesiology, University of Rochester School of Medicine and Dentistry, Rochester, New York.
zzzz
Department of Oncology, Harry J. Duffey Family Professor of Palliative Medicine, and Director of Palliative
Medicine, Johns Hopkins Medical Institutions, The Johns Hopkins Hospital, Baltimore, Maryland.
xxxx
Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, Washington.
{{{{
Department of Medicine, University of Texas Medical Branch, Galveston, Texas.
llllllll
Department of Anesthesiology and Psychiatry, University of Pittsburgh, Pittsburgh, Pennsylvania.
####
Department of Anesthesiology and Neurology, University of Alabama at Birmingham, Birmingham, Alabama.
Abstract: Current approaches to classification of chronic pain conditions suffer from the absence of a
systematically implemented and evidence-based taxonomy. Moreover, existing diagnostic approaches
typically fail to incorporate available knowledge regarding the biopsychosocial mechanisms contributing
to pain conditions. To address these gaps, the Analgesic, Anesthetic, and Addiction Clinical Trial Transla-
tions Innovations Opportunities and Networks (ACTTION) public-private partnership with the U.S. Food
and Drug Administration and the American Pain Society (APS) have joined together to develop an
evidence-based chronic pain classification system called the ACTTION-APS Pain Taxonomy. This paper de-
scribes the outcome of an ACTTION-APS consensus meeting, at which experts agreed on a structure for
this new taxonomy of chronic pain conditions. Several major issues around which discussion revolved
are presented and summarized, and the structure of the taxonomy is presented. ACTTION-APS Pain Tax-
onomy will include the following dimensions: 1) core diagnostic criteria; 2) common features; 3) common
medical comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative
neurobiological and psychosocial mechanisms, risk factors, and protective factors. In coming months,
expert working groups will apply this taxonomy to clusters of chronic pain conditions, thereby developing
a set of diagnostic criteria that have been consistently and systematically implemented across nearly all
common chronic pain conditions. It is anticipated that the availability of this evidence-based and mecha-
nistic approach to pain classification will be of substantial benefit to chronic pain research and treatment.
Perspective: The ACTTION-APS Pain Taxonomy is an evidence-based chronic pain classification
system designed to classify chronic pain along the following dimensions: 1) core diagnostic criteria;
2) common features; 3) common medical comorbidities; 4) neurobiological, psychosocial, and func-
tional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors,
and protective factors.
ª 2014 by the American Pain Society
Key words: Taxonomy, chronic pain, pain classification, biopsychosocial, evidence-based, mechanism-
based pain classification.
T
he purpose of clinical diagnosis is to provide a valid
explanation of symptoms and signs in order to
guide treatment and inform prognosis. Several
characteristics of an ideal diagnostic system are pre-
sented in Table 1. Although clinical diagnosis in many
fields has progressed considerably in recent decades,
incorporating new evidence and improved diagnostic
technologies, classification of pain disorders has wit-
nessed limited advances. Indeed, one could argue that
current pain classification systems fail to fulfill the pri-
mary purpose of diagnosis (to guide treatment) and
meet few of the characteristics of ideal classification sys-
tems. A challenge for pain classification is the need to
account for individual differences in pain processing,
which often result in a weak association between typical
‘diagnostic’ measures of tissue damage or disease activ-
ity and the severity and clinical symptoms. The most
comprehensive pain classification system available is
published by the International Association for the Study
of Pain (IASP). First published in 1979, revised in 1994,
and updated in 2011, the IASP system intended to fulfill
a mission described by IASP founder John Bonica, who
said, ‘It is possible to . develop a classification of pain
syndromes which are acceptable to many . in the field;
even if the adopted definitions and classifications are not
perfect they are better than the Tower of Babel condi-
tions that currently exist’ (p. ix).
16
However, although it
describes a large number of chronic pain conditions,
this system has never been widely adopted by either
the clinical or the research community. Notably, over
the past 15 years, multiple authors have called for a
mechanism-based approach to pain diagnosis
21-24
;
however, information regarding neurobiological
mechanisms is limited and has not been routinely
incorporated into any existing pain classification
systems. Thus, there is an increasingly urgent need to
develop a standardized, systematic, and evidence-based
approach to pain classification that incorporates infor-
mation regarding biopsychosocial mechanisms and that
can be applied to all common chronic pain conditions.
To that end, the Analgesic, Anesthetic, and Addiction
Clinical Trial Translations Innovations Opportunities
242
The Journal of Pain The ACTTION-APS Pain Taxonomy (AAPT)
and Networks (ACTTION) public-private partnership with
the U.S. Food and Drug Administration and the American
Pain Society (APS) have joined together to develop a clas-
sification system that incorporates current knowledge of
biopsychosocial mechanisms, called the ACTTION-APS
Pain Taxonomy (AAPT). The overriding objective of
AAPT is to develop an evidence-based chronic pain tax-
onomy based on a consistently applied multidimensional
framework and then to encourage experts to apply this
multidimensional framework to specific chronic pain
conditions. A major impetus for the AAPT initiative
derived from observing the transformative impact of
evidence-based diagnostic classifications in related
fields. For example, the third edition of the Diagnostic
and Statistical Manual of Mental Disorders (DSM-III) of
the American Psychiatric Association arguably revolu-
tionized research and clinical practice in psychiatry by
systematically implementing an evidence-based and
descriptive taxonomy to replace prior theoretically based
approaches that did not have adequate reliability and
were not widely used.
1,15
The DSM-III unveiled a multi-
axial system wherein specific diagnostic criteria were
presented on Axes 1 and 2, and the remaining axes al-
lowed the diagnostician to provide additional clinically
relevant information, including comorbid medical condi-
tions, psychosocial stressors, and overall functioning. The
DSM has seen further developments in subsequent edi-
tions, including the recently released DSM-5,
2
and it re-
mains an evidence-based descriptive taxonomy that is
universally applied in psychiatry. Thus, DSM-III and subse-
quent updates served as an exemplary model for AAPT.
Another successful diagnostic system from which AAPT
drew guidance is the International Classification of
Headache Disorders (ICHD), an evidence-based system
for classifying headaches.
17,18
The ICHD, now in its
third edition,
19
was first released in 1988 and has been
a tremendous boon to headache research and clinical
practice. The ICHD is the gold standard for headache
research, including clinical trials, which has led to the
development of evidence-based treatments for several
headache disorders.
There are multiple benefits to developing a unified
and standardized evidence-based taxonomy for classi-
fying chronic pain disorders. First, to the extent
possible, it can help align current knowledge of bio-
psychosocial mechanisms with an evidence-based pain
taxonomy, and subsequently with tailored pain treat-
ment. As previously described,
24
current pain classifica-
tion is based primarily on symptoms, signs, and body
location, sometimes combined with information
regarding structural pathology (eg, magnetic resonance
imaging evidence of spinal stenosis), and rarely in an in-
tegrated biopsychosocial framework. However, pain
treatments produce their therapeutic effects by impact-
ing specific neurobiological and/or psychosocial mecha-
nisms. Hence, an integrated biopsychosocial taxonomy
that includes current and emerging evidence regarding
pain mechanisms can assist clinicians with treatment se-
lection, thereby enhancing patient outcomes. Second, a
taxonomy in which diagnostic criteria for all chronic
pain conditions are consistently and systematically im-
plemented will facilitate communication about chronic
pain and related research by ensuring comparability
across studies of the same condition. That is, at present,
case definitions of the same chronic pain condition vary
widely across professional organizations and studies,
which limits the ability to compare findings across
studies. A widely accepted, consistently applied, and
evidence-based taxonomy would help overcome this
impediment to research and ultimately treatment. In
particular, a systematically implemented taxonomy
could enhance clinical trial methodology by promoting
consistently applied inclusion criteria, thereby facili-
tating treatment development. Third, AAPT would pro-
vide educational benefits because this systematically
developed taxonomy would represent an excellent
evidence-based and mechanistic foundation for
training pain researchers and clinicians. Finally, by iden-
tifying gaps in the evidence regarding diagnostic symp-
toms of particular disorders and their neurobiological
and psychosocial underpinnings, such a taxonomy could
highlight important avenues for future pain research.
Methods
In order to develop the multidimensional framework
and chronic pain taxonomy, AAPT held a consensus
meeting in May 2013 that brought together clinical
and basic scientists with expertise in pain mechanisms
and in the major chronic pain disorders in both adults
and children. In order to facilitate the process, a set of
foundational papers was distributed to all participants
prior to the meeting and the agenda included back-
ground presentations addressing the following topics:
1) the importance of pain mechanisms in chronic pain
classification (F.P., P.W.M.); 2) the development and evo-
lution of DSM to illustrate a successful classification
developed outside the area of pain; 3) 3 presentations
Table 1. Characteristics of an Ideal Diagnostic System
CHARACTERISTIC DESCRIPTION
Biologically plausible The diagnostic system must be consistent with the biological processes underlying the signs and symptoms
that characterize the disorders of interest.
Exhaustive The diagnostic system must encompass all clinical disorders within the domain of interest.
Mutually exclusive The diagnostic system must encode each disorder once and only once.
Reliable The diagnostic system must be applicable with a high degree of consistency across time and between
diagnosticians.
Clinically useful The diagnostic system must be useful in the clinical setting, guiding prognosis and therapy.
Simple The diagnostic system must be both straightforward and efficient enough for practical use.
Fillingim et al The Journal of Pain 243
describing successful efforts in developing evidence-
based diagnostic criteria for specific pain disorders,
namely, temporomandibular disorders (TMD; S.F.D.),
complex regional pain syndrome (S.B.), and chronic
pain associated with spinal cord injury (E.W.-N.); and
finally, 4) guiding principles for developing a new
chronic pain taxonomy (R.B.F.). The remainder of the
meeting was devoted to building consensus regarding
the multidimensional framework and the organization
of the taxonomy and the chronic pain disorders to which
the framework would be applied. During the course of
discussion, several important issues arose, which will be
described individually below.
Review of Recently Developed Evidence-
Based Diagnostic Criteria for Specific
Pain Disorders
To provide examples of implementing an evidence-
based approach to pain classification, 3 investigators
who were involved in different initiatives to develop
evidence-based diagnostic criteria for 3 different pain
disorders presented their approach and findings. S.F.D.
discussed the development of the Research Diagnostic
Criteria (RDC) for Temporomandibular Disorders (RDC/
TMD).
7
The RDC/TMD aimed to 1) develop standardized
diagnostic criteria for major TMD subtypes to be widely
used in research, 2) provide reliable specifications for
clinical examination and history, 3) use 2 axes to reflect
physical disease (Axis I) and subjective illness experience
(Axis 2), and 4) invoke an iterative research process
modeled after the DSM, which requires periodically
reestablishing the evidence-based reliability and validity
of the newly emerging iterations of the RDC/TMD. Each
of these objectives has been met, and the newest version
to evolve is the DC-TMD-1, an evidence-based diagnostic
and classification system for common forms of TMD
scientifically suitable for clinical practice as well as
research. Thus, the RDC/TMD has evolved to become
the gold standard for classification of TMDs in both
research and clinical settings. S.B. presented his experi-
ence regarding the development of revised diagnostic
criteria for complex regional pain syndrome.
10,11
Based
on an external validation study conducted across
multiple sites in Europe and North America, the
prevailing IASP consensus criteria were found to have
poor specificity, leading to potential overdiagnosis of
complex regional pain syndrome. An expert panel
developed new diagnostic criteria, which on
subsequent validation were found to have much
greater specificity than the IASP criteria, and these new
criteria were adopted by IASP in 2011. E.W.-N. presented
the International Spinal Cord Injury Pain Classification,
an effort to reconcile the multiple spinal cord injury
pain taxonomies present at the time in order to develop
valid diagnostic criteria for pain associated with spinal
cord injury.
3,4
The newly developed classification
incorporated feedback from multiple professional
organizations and was subsequently validated using
clinical vignettes. These 3 efforts in pain classification
demonstrate the feasibility and utility of adopting an
evidence-based approach in developing a pain taxon-
omy. However, each classification system differs substan-
tially from the others, reflecting the absence of an
overarching framework for pain classification. AAPT
has established such a framework in order to produce a
consistent pain taxonomy that includes all common
chronic pain disorders.
Important Characteristics of the AAPT
Taxonomy
The single most important characteristic of the taxon-
omy is that it be based on the best available evidence
rather than based solely on consensus or expert opinion.
That is, to the greatest extent possible, diagnostic criteria
for specific chronic pain disorders should be determined
using existing mechanistic and diagnostic evidence,
rather than historical precedent or theoretical biases.
When necessary, additional data will be collected to pro-
vide the required evidence to guide the working group
in developing diagnostic criteria. It is acknowledged
that the classification will evolve and be revised on the
basis of accumulating evidence and knowledge (as in
the evolution of DSM-III). It is also important to note
that AAPT proposes a coordinated effort to implement
the taxonomy systematically across all common chronic
pain conditions. Another critical characteristic of the
taxonomy is that it reflects the multidimensional and
biopsychosocial nature of chronic pain in which relevant
psychological and social variables are integrated with
neurophysiological knowledge. Thus, the template for
the AAPT taxonomy includes not only pain-related diag-
nostic criteria and features but also psychosocial features
and functional impact of pain conditions. Additionally,
AAPT emphasizes the inclusion of existing information
regarding mechanistic features and risk factors for pain
conditions, including not only neurobiological processes
but also psychosocial contributions, which are consid-
ered mechanisms in their own right. Another essential
characteristic is that the taxonomy should be applicable
for both research and clinical purposes, such that the
diagnostic criteria could be as easily used by primary
care providers as by pain scientists; however, it is recog-
nized that widespread clinical use is likely to develop
gradually as the evidence base expands and the taxon-
omy evolves further. Although the taxonomy is not de-
signed with consideration of factors related to billing
or third-party reimbursement for clinical services, au-
thors of diagnostic criteria for each condition will
attempt to provide information regarding international
classification of diseases (ICD) codes that are related to
the AAPT condition being described. Finally, the taxon-
omy is meant to be a starting point based on currently
available evidence, and the goal is to systematically up-
date the criteria as new evidence, especially regarding
neurobiological mechanisms, becomes available. Indeed,
it seems likely that refinements and enhancements to the
criteria will occur according to the experience of the
working groups in applying the taxonomy to specific
pain conditions.
244
The Journal of Pain The ACTTION-APS Pain Taxonomy (AAPT)
Should the New Taxonomy Be an
Evolution or a Revolution?
An important topic of discussion related to whether the
new taxonomy should significantly depart from current
and historical practice versus retaining features of current
approaches to classification. Proponents of the former
argued that current approaches reflect descriptive systems
organized on the basis of an inconsistently applied combi-
nation of body location, affected tissues, and associated
disease states, which provides little information regarding
the pathophysiological mechanisms underlying the
pain itself that should in principle be the targets of treat-
ment. Moreover, this approach treats chronic pain disor-
ders that often share biopsychosocial mechanisms (eg,
fibromyalgia, irritable bowel syndrome, and TMDs)
as completely independent.
5,20
Thus, a revolutionary
approach to chronic pain taxonomy might completely
abandon current diagnostic labels and approaches based
on anatomical structures and organ systems in favor
of an approach that prioritizes the neurobiological
mechanisms underlying chronic pain disorders. Although
there was unanimity regarding the importance of
incorporating pathophysiologic mechanisms into the
new taxonomy, 2 concerns prevented endorsement of a
revolutionary approach based primarily if not exclusively
on mechanisms. First, there was agreement that existing
knowledge regarding the mechanisms underlying many
chronic pain disorders was insufficient to support such
an approach. Second, there was concern that such a
radical departure from prevailing practice would face
resistance from clinicians and scientists who are familiar
with classical systems and who would be reluctant to
accept a significant change from current approaches.
Therefore, the consensus dictated that the AAPT would
retain similarities to existing systems, but, as exemplified
by the RDC/TMD to DC-TMD-1 evolution, the AAPT
approach would incorporate existing and emerging
evidence regarding neurobiological and psychosocial
mechanisms into all diagnostic criteria.
Should AAPT Adopt a Medical or a
Syndromal Approach to Pain
Classification?
Medical diagnostic approaches (eg, ICD-10) prioritize
identification of pathophysiological mechanisms,
whereas syndromalapproaches (eg, DSM-V) classify condi-
tions primarily based on clusters of symptoms. Arguably,
AAPTrepresents a hybrid of these 2 approaches. Although
the AAPT Core Diagnostic Criteria (Dimension 1) dictate
that signs and symptoms represent the primary basis on
which diagnoses will be based, the taxonomy also includes
Dimension 4, on which biopsychosocial mechanisms
contributing to the condition can be delineated.However,
it is important to recognize that the AAPT mechanistic
dimension differs from the historical biomedical view of
the pathophysiology of pain conditions, which empha-
sized peripheral markers of structural pathology and/or
disease severity. These pathophysiologic measures have
generally corresponded poorly to chronic pain severity
and have failed to account for interindividual variability
in clinical symptoms. In contrast, AAPT intends the mecha-
nistic dimension to specify the neurobiological and psy-
chosocial factors that contribute to the development of
chronic pain and account for the robust individual differ-
ences in clinical presentation that are a hallmark of chronic
pain. Indeed, given the subjective and personal nature of
the pain experience, a solely medical/pathophysiological
approach to pain classification seems neither realistic nor
advisable. Thus, ultimately, AAPT represents a syndromal
taxonomy that incorporates existing information
regarding mechanisms, while recognizing the importance
of individual differences in clinical presentation. This
approach is designed to produce a practically useful and
evidence-based taxonomy that allows a person-centered
approach to classification and clinical care.
How Should Chronic Pain Disorders Be
Categorized in the Taxonomy?
Considerable discussion addressed the basis upon
which chronic pain disorders would be grouped in this
taxonomy. For example, should conditions be grouped
by anatomical locations (eg, upper extremity, lower
extremity, spine) or by organ system (eg, nervous system,
musculoskeletal, visceral)? Relying on anatomical site
alone was rejected, because this would cluster together
chronic pain conditions that have very distinct patho-
physiological mechanisms. For instance, lower extremity
pain would include peripheral diabetic neuropathy of
the foot and leg as well as knee osteoarthritis.
Conversely, the same disorder affecting different
anatomical sites (eg, peripheral diabetic neuropathy of
the foot and hand) would be separately categorized.
Therefore, the consensus was that the dimension along
which pain disorders will be categorized is organ sys-
tem/anatomical structure, which will include peripheral
Table 2. Organization of Chronic Pain Disorders
to Be Included in the AAPT*
Peripheral and central nervous systems
Peripheral neuropathic pain
Central neuropathic pain
Musculoskeletal pain system
Osteoarthritis
Other arthritides (eg, rheumatoid arthritis, gout, connective tissue
diseases)
Musculoskeletal low back pain
Myofascial pain, chronic widespread pain, and fibromyalgia
Other predominantly musculoskeletal pain
Orofacial and head pain system
Headache disorders*
Temporomandibular disorders
Other orofacial pain
Visceral, pelvic, and urogenital pain
Visceral pain: abdominal, pelvic, and urogenital pain
Disease-associated pains not classified elsewhere (eg, pain associated
with active cancer, with sickle cell disease, or with Lyme disease)
*AAPT will not develop diagnostic criteria for headache condition, because the
ICHD-2 already exists and provides an evidence-based classification that is highly
consistent with the AAPT template.
Fillingim et al The Journal of Pain 245
and central neuropathic pain, musculoskeletal pain, and
pelvic/urogenital and visceral pain (see Table 2). Finally, it
was recognized that certain types of disease-related pain
may not be included in one of the other categories;
therefore, a category was created for disease-related
pains not classified elsewhere (eg, pain associated with
active cancer, sickle cell disease, and Parkinson’s disease).
The preference is to classify disease-related pain in one of
the primary organ system/anatomical categories (eg,
painful diabetic peripheral neuropathy would be cate-
gorized as a peripheral neuropathic pain); however,
when this is not possible, the pain disorder will be classi-
fied in the disease-related pain category. It is also impor-
tant to note that headache disorders were intentionally
excluded from the present taxonomy, because the ICHD
has been carefully and systematically developed and
there was agreement that the existing criteria fully
meet the standards of the AAPT.
Results
After considerable discussion, a multidimensional
framework for the new chronic pain taxonomy was
developed. The dimensions comprising the AAPT frame-
work, which will be applied to each chronic pain disorder
(see Table 2), are presented in Table 3. Each dimension
will be discussed in greater detail below. It is important
to recognize that the order of the dimensions is not
intended to reflect their priority or significance. Indeed,
the consensus meeting unanimously endorsed the
importance of Dimension 5, reflecting underlying mech-
anisms. However, this Dimension was not included as
part of the essential diagnostic criteria, because current
evidence provides definitive mechanistic information
for very few chronic pain disorders.
Dimension 1: Core Diagnostic Criteria
The core diagnostic criteria reflect those signs, symp-
toms, and test results that form the basis of the diagnosis.
Ideally, the core diagnostic criteria should be applied in
an algorithmic manner, such that people meeting these
specific criteria would be classified as having the disor-
der. Signs and symptoms would include diagnostic
nonpain features (eg, diminished range of motion,
edema, altered sensation) and pain-related characteris-
tics (eg, pain descriptors, location, and temporal quali-
ties) that are considered pathognomonic of the
disorders. For example, based on RDC/TMD, diagnostic
symptoms of TMD might include periauricular pain,
whereas diagnostic clinical signs could include palpation
sensitivity, reduced pain-free range of motion, and joint
sounds (eg, popping or clicking).
7
In addition, for some
disorders, the results of clinical or laboratory tests will
be incorporated into the diagnostic criteria. Finally, dif-
ferential diagnoses are also considered in Dimension 1.
Dimension 2: Common Features
This dimension is intended to provide additional
descriptive information regarding the disorder by
including common features that often characterize the
disorder but are not required for the diagnosis. For
example, a given chronic pain disorder might commonly
be associated with pain occurring in a specific body loca-
tion (eg, diabetic neuropathy pain in the feet) or
described in a particular way (eg, burning or shooting);
however, these features would not be a requirement
for making the diagnosis. In addition to pain-related
qualities, this dimension will also include information
regarding nonpainful features as well as information
regarding the epidemiology of the disorder.
Dimension 3: Common Medical
Comorbidities
This dimension provides information regarding medi-
cal and psychiatric conditions that are often comorbid
with, but not required for diagnosis of, the chronic
pain disorder. For example, if major depression and
generalized anxiety disorder are considerably more com-
mon in patients with a specific pain disorder than in the
general population, then these would be noted as
Table 3. The Dimensions Comprising the AAPT
DIMENSION DESCRIPTION
Dimension 1: Core diagnostic criteria Includes symptoms and signs required for diagnosis of the disorder (eg, periauricular pain,
palpation sensitivity, joint sounds in the case of TMD). Also includes diagnostic tests and
differential diagnosis considerations.
Dimension 2: Common features Provides additional information regarding the disorder, including common pain
characteristics (eg, location, temporal qualities, descriptors), nonpain features
(numbness, fatigue), and the epidemiology of the disorder. These features are helpful in
describing the disorder but are not used as part of the diagnosis.
Dimension 3: Common medical comorbidities Includes medical diagnoses that co-occur with high frequency with the pain disorder. For
example, diabetes mellitus is often comorbid with osteoarthritis, and major depression is
comorbid with many chronic pain disorders.
Dimension 4: Neurobiological, psychosocial,
and functional consequences
Includes information regarding neurobiological and psychosocial consequences of chronic
pain, as well as the functional impact of the pain disorder. Examples include allostatic
load, sleep quality, mood/affect, coping resources, physical function, and pain-related
interference with daily activities
Dimension 5: Putative neurobiological
and psychosocial mechanisms, risk factors,
and protective factors
Includes putative neurobiological and psychosocial mechanisms contributing to the pain
disorder, including potential risk factors and protective factors.
246 The Journal of Pain The ACTTION-APS Pain Taxonomy (AAPT)
psychiatric comorbidities. Similarly, Sj
ogren’s syndrome
could be included as a medical condition that is
commonly comorbid with burning mouth syndrome.
Dimension 4: Neurobiological,
Psychosocial, and Functional
Consequences
The neurobiological, psychosocial, and functional
consequences of chronic pain disorders have been well
documented, and these will be included in Dimension
4. Indeed, some individuals may meet diagnostic criteria
for a given pain disorder though their neurobiological,
psychosocial, and physical function remain excellent,
whereas other patients with the disorder may present
with considerable dysfunction across one or more of
these domains. Thus, psychosocial and functional fea-
tures could be used for subgrouping individuals within
a given pain disorder, which could have important
treatment implications. Importantly, premorbid psycho-
social functioning represents a consistent predictor of
the development of chroni c pain; however, psychologi -
cal antecedents of the pain disorder, which could reflect
causal risk factors, will be specified on Dimension 5
(see below). We recognize that the distinction
between causes and consequences will be challenging
when applying the taxonomy. However, we also believe
it is important to acknowledge that neurobiological
and psychosocial differences between chronic pain
cases and controls can reflect both causes (or risk
factors) and consequences of chronic pain. For example,
altered neurosensory processing, as measured by
quantitative sensory testing, has predicted future
development of chronic pain in some studies.
6,25
However, other research has demonstrated that successful
treatment of pain normalizes quantitative sensory testing
responses.
9,12,13
Hence, the neurobiological underpinnings
of altered pain processing may be a risk factor for pain in
some cases and a consequence of pain in other cases. A
similar scenario exists for psychological factors as well,
because data support that depression, for example, is a
risk factor for pain developme nt and that chronic pain is a
risk factor for development of depression.
8,14
Thus, we
believe it is important that the taxonomy incorporates the
bidirectional nature of these associations. These issues
will be addressed on a case-by-case basis for each pain con-
dition. Information reflected on this dimension may be
derived from the clinical examination or via administration
of psychometric instruments designed to assess these do-
mains.
Dimension 5: Putative Mechanisms, Risk
Factors, and Protective Factors
This dimension is intended to provide information
regarding the potential neurobiological and psychoso-
cial mechanisms and risk factors contributing to chronic
pain disorders. This includes neurobiological mecha-
nisms, such as specific molecular or neurochemical path-
ways that have been demonstrated to contribute to the
disorder. Risk or protective factors might include specific
genetic polymorphisms. Based on current evidence,
information regarding specific mechanisms and risk
factors may not be available for some chronic pain disor-
ders; however, more general information may be avail-
able. For example, it is widely accepted that
fibromyalgia is characterized by generalized hypersensi-
tivity to painful stimuli, though the precise mechanisms
underlying this phenotype remain unknown. In this
instance, widespread hypersensitivity could be included
as a potential mechanism or risk factor.
In addition to traditional neurobiological mechanisms,
psychosocial factors also represent important pain mech-
anisms and risk factors to be considered in the taxonomy,
including potential protective factors (eg, social support,
optimism, coping). It is recognized that psychosocial
influences on pain must be transduced through more
proximal neurobiological processes, though these spe-
cific mechanisms may not be well understood. For
example, fear-avoidance processes can contribute to
pain and pain-related disability not only at a behav-
ioral/functional level but also at a neurobiological level.
For each pain disorder, available and recommended
methods for assessing psychosocial and neurobiological
mechanisms will be described. Moreover, it is anticipated
that new information regarding specific neurobiological
and psychosocial risk factors and mechanisms for many
pain disorders will rapidly emerge, based on genetic as-
sociation studies, brain imaging research, quantitative
sensory testing, and additional psychosocial mechanistic
research. Thus, the intent is that the diagnostic criteria
will be updated with this information on an ongoing
basis.
Organization of Chronic Pain Disorders
The consensus meeting next turned its attention to
organizing the chronic pain disorders that would be
included in the taxonomy. As noted above, there was
considerable discussion regarding the best approach
for categorizing the pain disorders, and the final
consensus was that chronic pain disorders would be
primarily categorized by anatomical/organ system (see
Table 2). There are limitations to this approach to cate-
gorization. For example, TMDs could be considered
musculoskeletal pains. Therefore, in developing the
diagnostic criteria for each chronic pain disorder, the
expert working groups will attempt to address features
of the condition that may overlap with other conditions
within and across categories. For instance, generalized
hypersensitivity to painful stimuli can characterize
chronic pain disorders across virtually every category,
and this feature is likely relevant to the underlying
pathophysiology of many chronic pain disorders. By
highlighting these potentially overlapping features, it
may be possible to build clusters of conditions based
on underlying pathophysiological and psychosocial
mechanisms.
Next Steps
This article presents the structure and organization of
the proposed taxonomy, based on the outcomes of our
Fillingim et al
The Journal of Pain 247
consensus meeting. The AAPT Steering Committee has
now identified leaders for each of the individual work-
ing groups who will apply the taxonomy to each group
of conditions specified in Table 2. The working group
leaders will proceed as follows: 1) identify and invite
other experts to be included in the working group, and
convene a working group meeting; 2) identify the most
common pain conditions within the working group’s
purview for which diagnostic criteria will be specified;
3) review the existing literature regarding current and
previously proposed diagnostic criteria for each of the
major disorders (including strengths/weaknesses of
each); 4) propose a comprehensive list of potential signs
and symptoms for each of the pain conditions identified
in point 2 (It is anticipated that at this point all working
groups will reconvene in order to facilitate development
of draft diagnostic criteria for each chronic pain condi-
tion.); 5) complete studies to demonstrate the reliability
and validity of the proposed diagnostic methods and
criteria; and 6) finalize the diagnostic criteria for each
chronic pain condition based on the outcomes of the
validation studies and submit a manuscript to a peer-
reviewed journal. Working group activities will be over-
seen and supported by both an Executive Committee and
a Research Committee.
Conclusions
Classification of chronic pain disorders has historically
been a clinically driven and piecemeal exercise, and a
more systematic and evidence-based approach to chronic
pain diagnosis would confer considerable scientific,
clinical, and educational benefit. We have proposed a
multidimensional chronic pain taxonomy that will be
evidence-based and systematically applied to all common
chronic pain disorders. Notably, AAPT explicitly includes a
dimension on which information regarding neurobiolog-
ical and psychosocial mechanisms will be provided. AAPT
working groups will use this taxonomy to develop
evidence-based diagnostic criteria for most chronic pain
disorders, which are intended for both research and clinical
use. The intent is for AAPT to be a dynamic and evolving
taxonomy that will be updated and revised as new evi-
dence emerges. As has been the case with other newly
developed taxonomies, AAPT may initially be most widely
used in research settings, but as the taxonomy evolves it
is expected that more widespread clinical use will follow.
It is hoped that AAPTwill produce robust scientific and clin-
ical impact on the chronic pain field, similar to the transfor -
mative influence of DSM-III and ICHD on research and
treatment in mental health and headache, respectively.
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