The IASP Classification of Chronic Pain for ICD-11: Chronic Primary Pain

Michael Nicholas; Johan W.S. Vlaeyen; Winfried Rief; Antonia Barke; Qasim Aziz; Rafael Benoliel; Milton Cohen; Stefan Evers; Maria Adele Giamberardino; Andreas Goebel; Beatrice Korwisi; Serge Perrot; Peter Svensson; Shuu-Jiun Wang; Rolf-Detlef Treede; The IASP Taskforce for the Classification of Chronic Pain

Disclosures

Pain. 2019;160(1):83-87. 

In This Article

Discussion

Chronic primary pain is a new diagnosis in the ICD-11 classification for chronic pain that is intended to embrace a number of poorly understood conditions while avoiding obscure and potentially laden terms such as "somatoform," "nonspecific," or "functional." Chronic primary pain syndromes can be conceived as health conditions in their own right, whereas in the other 6 groups of chronic pain conditions (chronic secondary pain syndromes), pain may be considered a symptom of some other underlying diseases.[55] The distinction between "primary" and "secondary" has been transferred from the International Headache Classification.[22] It avoids designating the basis of the pain as "psychological" or "organic" because chronic pain necessarily includes psychological and social dimensions in addition to the biological components.[60]

Recently, in addition to nociceptive and neuropathic mechanisms, the concept of "nociplastic" was introduced as a third neurophysiological mechanism underpinning some chronic pain conditions.[26] It has been suggested that it may be particularly applicable to CPP. However, at this stage, the relationship of nociplastic pain mechanisms and chronic primary or secondary pain syndromes cannot be determined. Further development of the application of this new descriptor is in progress. However, it should be noted that it does require clinical and psychophysical findings suggestive of altered nociceptive function, and that it does not apply to patients reporting pain without hypersensitivity.

Like the other diagnoses proposed for ICD-11, CPP can be combined with optional specifiers, such as the presence of psychological and social factors and pain severity (combined ratings for pain intensity, distress, and disability). The severity ratings can be coded, and it is hoped that their dimensional nature will facilitate not only clinical communication but also interpretation of research findings. By means of these specifiers, clinicians and researchers will be able to determine whether their samples are similar to those participating in other studies that use these codes. For example, instead of describing a sample of patients as having low-back pain, researchers using ICD-11 will also be able to distinguish levels of severity (mild, moderate, and severe) that help guide treatment (or no treatment). These codes also provide clinicians in both primary care and more specialized facilities with a simple means for evaluating changes over time in their chronic pain patients.[47]

Naturally, the new classification of chronic pain will have to be shown to be reliable and clinically useful. The next step in the development of ICD-11 will be to encourage field trials to establish the psychometric properties of these codes and their utility. A pilot field trial in 4 countries yielded CPP and chronic secondary musculoskeletal pain as the 2 most frequent diagnostic groups, which were clearly distinguishable by both pain specialists and primary care physicians. Because the categories are more descriptive than former distinctions between "psychological and somatic" pain conditions, we expect that future evaluations will confirm higher retest reliability and inter-rater reliability compared with the previous approaches of classification.

The proposal in this article is that all chronic pain diagnoses should be presented in ICD-11 as a coherent category of diagnoses and not be divided up artificially as is the case in ICD-10. This confers a number of advantages, including when the categories are used for the worldwide collection of data for health statistics. For these statistics, different levels of granularity can be chosen. Chronic pain may be divided into primary vs 6 subtypes of secondary pain syndromes (level 1 in Figure 1), or any of these top level chronic pain diagnoses is subdivided into one of their level 2 diagnoses (Figure 1 here and in companion articles). The World Health Organization plans for member states to report their health statistic from 2022 onwards using level 1 and 2. We expect that this will be a useful level of aggregation, in that it provides a category for pain conditions that have hitherto been counted in less useful ways by being dispersed throughout the ICD. This represents chronic pain in health statistics, which influence health policies and allocation of resources for prevention, treatment, and rehabilitation as well as research.

The new ICD-11 CPP classification is also expected to enhance pain management outcomes, in that it allows for inferences about unknown aspects of an individual who has been assigned a specific pain category.[40] Indeed, given a pain (sub)category, clinicians and researchers can infer likely causes of symptoms, predict most likely consequences, estimate a timeline, the most likely future developments, and optimize treatment plans for that person. In the case of CPP, in particular, the identification of physiological, psychological, and social contributors to pain is specifically encouraged, and this opens the way for multimodal interventions that can address these factors and potentially enhance treatment outcomes. The German experience with the national variant code F45.41 (chronic pain with somatic and psychological factors) suggests that few large chronic pain diagnoses are more useful to guide treatment and its funding than the numerous more specific ones scattered throughout ICD-10.[39]

Multimodal pain management is regarded as the most helpful treatment form for chronic pain. How many "variants" of multimodal pain management will be needed in the future is an important research issue. It applies to both primary and secondary pain syndromes. It is expected that the diagnoses of the new classification may be helpful in performing this research program by offering a more helpful grouping of the diagnoses. On the other hand, it should be recognized that any categorization may introduce an assimilation bias[52,62] that may draw attention away from idiosyncratic features of the individual that may be important for an adequate personalized pain medicine. ICD-11 users should be aware of this potential bias to limit its impact.

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