A Five-Dimensional View of Pain

Progress report on ACTTION/APS Pain Taxonomy effort

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Leaders of a major effort to systematically classify all common chronic pain conditions expect to have the first stage completed by mid-July 2014. The Pain Taxonomy, a project of the ACTTION public-private partnership, and the American Pain Society is one of two independent initiatives launched last spring to fill a widely perceived need for an updated evidence-based approach to improve diagnosis, treatment, and research of chronic pain (see PRF related news story).

Key issues and decisions of the initial consensus meeting held in May 2013 are summed up in the March 2014 issue of The Journal of Pain. The paper also describes the organizing principles, structured framework, and working outline for the final product.

“We had a lot of discussion about how revolutionary to be,” said Roger Fillingim, director of the University of Florida Pain Research and Intervention Center of Excellence in Gainesville, US, and co-chair of the taxonomy initiative. In the end, the group decided the field lacked sufficient ammunition in the form of evidence to completely overthrow the prevailing diagnostic approach based on body location, affected tissues, and associated disease states.

“There was a lot of interest from virtually all the workgroup members in moving more toward a mechanism-based system,” Fillingim said. “But we all recognize that existing knowledge doesn’t support it. We don’t know enough about the mechanisms underlying pain conditions and symptoms to have that as the primary foundation of the taxonomy. Over the years, we hope [the Pain Taxonomy] will evolve such that the mechanistic aspects take higher priority than signs and symptoms.”

As a result, the group made neurobiological and psychosocial mechanisms one of the five dimensions to consider in the diagnosis of all chronic pain conditions. The other four dimensions are: core diagnostic criteria, such as symptoms and diagnostic tests; common features, including the epidemiology of the disorder; common medical comorbidities; and neurobiological, psychosocial, and functional consequences, such as the impact on sleep quality, mood, and interference with daily activities.

“Ultimately, [it] represents a syndromal taxonomy that incorporates existing information regarding mechanism, while recognizing the importance of individual differences in clinical presentation,” write the authors in the paper. “This approach is designed to produce a practically useful and evidence-based taxonomy that allows a person-centered approach to classification and clinical care.”

The Pain Taxonomy idea arose within the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration. The group paired up with the American Pain Society (APS) to develop the ACTTION-APS Pain Taxonomy (AAPT).

A parallel project is led by a task force of the International Association for the Study of Pain (IASP) co-chaired by a German team. They are working under the auspices of the World Health Organization (WHO) to generate the first chapter dedicated to pain for the next revision of the International Classification of Diseases (ICD). Some pain experts are volunteering for both projects, which keeps information flowing informally in both directions, Fillingim said.

The IASP task force has had several meetings, drafted a proposal for a classification system, and hopes to find an international consensus in a May 20 meeting in Frankfurt, co-chair Winfried Rief of the University of Marburg, Germany, told PRF by email. “A major goal is the development of a virtual chapter of pain diagnosis” for the ICD-11, Rief wrote. “At present, we have defined seven categories, such as cancer-related pain, neuropathic pain, or primary pain.” Rief characterizes the IASP/WHO draft as “slightly different” from the AAPT outline.

In the AAPT scheme, chronic pain disorders are organized into five major categories, including peripheral and central nervous systems; musculoskeletal pain; orofacial and head pain; visceral, pelvic, and urogenital pain; and disease-associated pains not classified elsewhere (such as cancer or sickle cell disease). Most of the categories have subsections—for example, the musculoskeletal category is broken down into osteoarthritis, other arthritides, low back pain, myofascial and fibromyalgia, and other musculoskeletal pain. For headaches, the orofacial and head pain category will defer to the International Classification of Headache Disorders (ICHD-2), which is, Fillingim and co-authors wrote, “the gold standard for headache research, including clinical trials, which has led to the development of evidence-based treatments for several headache disorders.”

In fact, while being designed for easy clinical use, diagnostic systems in pain and psychiatry started as research tools, and the group expects researchers to be the early adopters, Fillingim told PRF. “We have talked about that quite a bit in person at the meeting and by email and telephone in the intervening period to be clear in our own minds.” In a key benefit, the taxonomy will identify gaps in the evidence for diagnostic symptoms and underlying mechanisms, highlighting avenues for future pain research, the authors wrote.

At the May meeting, workgroups were set up around the categories. A steering committee and a research committee work across all categories, Fillingim said. At this stage, all the workgroups have leaders. Many have a full roster and have conducted the initial conference calls and emails to establish an agenda. The workgroups are charged with deciding which conditions they are going to cover and conducting systematic reviews of the existing literature to find out what is known about the classification of particular systems, he said. The reviews will inform the diagnostic criteria in the five dimensions for each chronic pain condition. “We have excellent workgroup leaders and really good people committed to getting the job done,” Fillingim said.

In mid-July, representatives from the workgroups will come together for a second meeting to report on progress in data collection for the reviews. They may begin discussing the design of clinical studies to validate the specificity and sensitivity of the new diagnostic criteria. The taxonomy will be published by subcategory as standalone papers on a staggered timeline as they are completed. The plan calls for eventually compiling them into one guide, Fillingim told PRF.

The initial criteria and classification schemes are meant to be living documents that can be updated as new information becomes available, but the updating mechanism has not been established. In fact, he said, the whole thing may need to be restructured in 10 to 20 years, when more knowledge has accumulated.

A more immediate unknown is the final form of the complete first edition. “The ultimate plan is to assemble it all in a unified document in an electronic form or an online system,” Fillingim said, “but there haven’t been any final decisions.”

As the content-based papers begin coming out, he said, the group will be eager for feedback from the pain research and clinical community.

Carol Cruzan Morton covers science, health, and the environment, and is based near Boston, Massachusetts, US.

(Originally published in Pain Research Forum at http://www.painresearchforum.org/news/39134-five-dimensional-view-pain)

 

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