Enormous collaborative effort sees chronic pain added to international disease coding system


Prof Milton Cohen AM

The following is a summary of a talk given by Professor Milton Cohen AM of St Vincent’s Clinical School, UNSW Sydney at the 39th Annual Scientific Meeting of the Australian Pain Society which took place from April 7-10, 2019, on the Gold Coast, Australia

Pain is one of the leading reasons why patients seek medical care. Chronic pain—pain that persists for three months—is a significant source of human suffering and disability. However, the prevalence of chronic pain as a health problem is not well reflected in standard health service data. In large part this is due to the way it has been coded. The main coding system for medical conditions used in Australia is he International Classification of Diseases (ICD) published by the World Health Organization (WHO).  Unfortunately, these have failed to reflect the phenomenon of chronic pain, such that related conditions were categorised in an unsystematic and often obscure manner.

At the Australian Pain Society’s 39th Annual Scientific Meeting Professor Milton Cohen AM, from St Vincent’s Clinical School at UNSW Sydney, presented an overview of the International Association for the Study of Pain (IASP) WHO Taskforce’s efforts on defining chronic pain for the 11th revision of the ICD coding system (ICD-11) on behalf of fellow Taskforce members Professors Stephan Schug (University of Western Australia) and Michael Nicholas (Royal North Shore Hospital, University of Sydney).

Current definitions have their limitations

Previous definitions of chronic pain have centred around the notion that it is pain that lasts beyond the normal expected healing time, and lacks the ‘alarm’ or ‘warning’ nature of acute pain. While these definitions may be appropriate to pain that occurs following surgery or trauma, the reasoning underlying them is difficult to apply in other conditions like chronic musculoskeletal or neuropathic pains. More recent definitions have included a temporal aspect, where chronic pain is defined as pain that lasts or recurs for more than three months.

The ICD is the preeminent tool used to code diagnoses, as well as to document investigations or therapies patients receive within healthcare systems. As the name suggests, the ICD is used by countries all over the world to report target diseases and relevant comorbidities in clinical research. The tenth revision of the ICD coding system (ICD-10) contains some diagnostic codes for chronic pain conditions. However, the existing codes are limited as they do not reflect the underlying epidemiology of chronic pain conditions and are not organised in any systematic or logical manner.

Due to this lack of an adequate and available set of codes for chronic pain, it is difficult to accurately collect epidemiological and clinical data related to pain on an international level.

Chronic pain as a new concept

To address these shortcomings, the IASP and WHO established a joint taskforce to generate a systematic and improved classification of chronic pain. The Task Force for the Classification of Chronic Pain—comprising pain experts from all over the world—spent many years developing and testing a novel and pragmatic classification of chronic pain for the 11th revision of the ICD coding system.

“The taskforce divided existing conditions of chronic pain into primary and secondary chronic pain”, explained Dr Cohen. “Chronic primary pain refers to conditions where the cause of pain is not confidently known or identified.” The three-month criterion remains for this new classification of pain, which exemplifies the sociopsychobiomedical framework in which pain is considered. This diagnosis requires that the pain must be associated with significant emotional distress or functional disability. Emphasis has been placed on removing the stigma associated with chronic pain conditions, while avoiding terms such as non-specific and somatoform. “These are codes for ‘I don’t really believe you’”, Dr Cohen pointed out.

The classification structure for chronic primary pain relates to the notion that pain can occur in any body site (e.g., face, low-back, pelvis, etc.), or across a combination of sites. “This is not rocket science,” Dr Cohen described, “but rather a pragmatic descriptive classification for situations in which we do not know aetiology or pathogenesis of the pain.” The broad categories of chronic primary pain include musculoskeletal, visceral, headache or orofacial, complex regional pain, and widespread pain. Importantly, biological or psychological contributors may be identified, but unless another diagnosis would better account for the presenting symptoms, the diagnosis of chronic primary pain would be chosen.

“The whole philosophy of secondary chronic pain syndromes is that pain should be coded simultaneously with another disease if that disease is present—even if that disease itself is a cause of pain”, Dr Cohen said. The secondary chronic pain syndromes in ICD-11 are also enshrined in a sociopsychobiomedical framework. These classifications follow the existing WHO lexicon when referring to diseases—they start at the aetiology if they can, before moving onto the mechanism and then the affected body site (if possible).

The six pragmatic clusters of secondary chronic pain conditions are identified according to this lexicon. Some secondary chronic pain syndromes—such as cancer-related, post-surgical, and post-traumatic pain—are clustered by the underlying aetiology. Others are determined by the mechanism involved, such as neuropathic pain, or by body site, such as visceral pain, headache or orofacial pain or musculoskeletal pain. The last of these, secondary musculoskeletal pain, can be further divided by mechanism (e.g., persistent inflammation, structural changes, or as a result of neurological disease or injury).

In addition to the broader labels, specifiers can be attached to chronic pain conditions. Specifiers can refer to the degree of pain severity, distress and interference a temporal dimension, and to the cognitive and behavioural factors involved.

“Another concept in the ICD-11 system is that of co-parenting—you could say it was a bastard of a concept”, Dr Cohen joked. As the name suggests, co-parenting refers to syndromes with multiple parents. “One example of co-parenting is chronic pain secondary to neuropathy induced by chemotherapy in the context of cancer”, explained Dr Cohen. This secondary pain syndrome has two clear parents—one is chronic cancer-related pain while the other is chronic neuropathic pain.

“Getting chronic pain into ICD-11 in its own right —and coding it- is a major step forward”, Dr Cohen summarised. The eleventh version of the ICD was released by the WHO in June 2018 and will be put into effect on January 1, 2022. While the transition will be slow, it will mark the culmination of many years hard work by the Task Force for the Classification of Chronic Pain—and an important step in the right direction towards having an internationally agreed, systematic way to classify chronic pain. This will have many important implications for patients, health care providers, researchers, and the provision of health services. Most significant of these is that patients should cease being invisible health care consumers as their pain conditions will be coded and recorded in health service statistics.

Lincoln Tracy is a postdoctoral research fellow in the School of Public Health and Preventive Medicine at Monash University and freelance writer from Melbourne, Australia. He is a member of the Australian Pain Society and enthusiastic conference attendee. You can follow him on Twitter (@lincolntracy) or check out some of his other writing on his website.

Related reading

  • A classification of chronic pain for ICD-11.

Treede, RD et al.
Pain, 2015.
Link to full text.

  • Chronic pain as a symptom or a disease: the IASP Classification of Chronic Pain for the International Classification of Diseases (ICD-11).

Treede, RD et al.
Pain, 2019.
Link to full text.

  • The IASP classification of chronic pain for ICD-11: chronic primary pain.

Nicholas, M et al.
Pain, 2019.
Link to full text.

About Australian Pain Society

The Australian Pain Society is a multidisciplinary body aiming to relieve pain and related suffering through leadership in clinical practice, education, research and public advocacy.


Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s