Besides the conceptual framework to describe the experience of functioning and disability, the ICF includes a classification with more than 1400 domains in the components body functions (8 chapters), body structures (8 chapters), activities and participation (9 chapters), and environmental factors (5 chapters). The personal factors are not classified in the ICF.
2.2. The components of the ICF
The components of the ICF are defined as follows19 (Table 1):
- (1) Body functions are the physiological functions of body systems (including psychological functions).
- (2) Body structures are anatomical parts of the body such as organs, limbs, and their components.
- (3) Impairments are problems in body function or structure such as a significant deviation or loss.
- (4) Activity is the execution of a task or action by an individual.
- (5) Participation is a person's involvement in a life situation.
- (6) Activity limitations are difficulties an individual may have in executing activities.
- (7) Participation restrictions are problems an individual may experience in involvement in life situations.
- (8) Environmental factors make up the physical, social, and attitudinal environment in which people live and conduct their lives.
Within the ICF framework, “functioning” is an umbrella term encompassing all body functions, activities, and participation, whereas “disability” is defined as an umbrella term for impairments, activity limitations, and participation restrictions.19 To facilitate the use of the ICF, so-called “core sets” were developed. A core set for a health condition X is a list of essential categories that are relevant for the description of the functioning of a person with condition X.
2.3. Representation of pain in ICF
In the ICF, pain is classified as a body function together with other sensory functions (Chapter 2 of body functions).19 The sensation of pain is described as “sensation of unpleasant feeling indicating potential or actual damage to some body structure” and includes “sensations of generalized or localized pain, in one or more body parts, pain in a dermatome, stabbing pain, burning pain, dull pain, aching pain, and impairments such as myalgia, analgesia, and hyperalgesia.”19 Please note that this definition in the ICF is close to, but not identical with, the IASP definition.8 Specifically, it implies a close link between the sensation of pain and the presence of a noxious stimulus (observable from a third person perspective), whereas the IASP definition is from a first person perspective and clarifies that anything that feels like pain is pain by definition.14
In the ICF, pain has the following domains:
- (1) Generalized pain (b2800)
- (2) Pain in body part (b2801), including pain in head and neck (b28010), pain in chest (b28011), pain in stomach or abdomen (including pain in the pelvic region) (b28012), pain in back (including pain in the trunk; low backache) (b28013), pain in upper limb (including hands) (b28014), pain in lower limb (including feet) (b28015), pain in joints (including small and big joints) (b28016), as well as pain in body part, other specified, (b28018), and pain in body part, unspecified, (b28019)
- (3) Pain in multiple body parts (b2802)
- (4) Radiating pain in a dermatome (b2803)
- (5) Radiating pain in a segment or region (b2804).
The ICF also includes the domain sensation of “pain, other specified and unspecified” (b289), “sensory functions and pain, other specified” (b298), and “sensory functions and pain, unspecified” (b299).
This view of pain as a limitation to functioning according to its location needs to be differentiated from the categorical diagnoses of chronic pain according to its etiology listed in the ICD-11. Within the ICD-11, chronic pain as a symptom (ie, chronic pain related to a specific disease) is distinguished from pain as a syndrome (ie, chronic pain as a problem in its own right). In the ICD-11 classification of chronic pain, “pain as a symptom” applies to chronic secondary pain syndromes, including secondary headaches, whereas “pain as a syndrome” applies to chronic primary pain syndromes, including primary headaches.15 In both cases, ICD-11 chronic pain conditions do not only document single symptoms, but also other information (eg, on etiology, course, and intensity) and inclusion/exclusion criteria.
Pain (b280) is also part of the generic set of the ICF applicable to all health conditions (Tables 2–4). However, the ICD-11 only cross-references “activities and participation domains” of the ICF.12 As part of the “body function” domains of the ICF, pain will not be cross-referenced in the “functioning properties” of all diagnoses in the ICD-11. Therefore, it is important that the new ICD-11 codes for chronic secondary pain syndromes are widely used to identify patients with chronic pain as a symptom of cancer, trauma, disease of the nervous system or internal organs, or the musculoskeletal system.15
3. Description of typical disabilities associated with chronic pain
According to the ICF, disability is defined as the negative aspect of functioning and includes the components body functions and structures as well as activities and participation (Table 1). The negative aspect of functioning at the level of body functions and structures is called “impairment,” whereas at the level of activities and participation, it is called “activity limitation” and “participation restriction,” respectively. For that reason, the typical disabilities associated with chronic pain should be described as impairments, activity limitations, and participation restrictions.
Many chronic pain patients have typical disabilities: they frequently experience depression, anxiety, sleep disturbance, fatigue, and waking unrefreshed among others.2,7,9,10 Moreover, many chronic pain patients also experience a deterioration in the quality of life (QoL), and high rates of other disabilities.7 At the impairment level, this includes changes in energy and drive, sleep, psychological, and motor functions. At the level of activity limitations and participation restriction, the most relevant areas include mobility, coping with stress, daily routines, workplace, recreation, family, and community life.
4. Development of a specific set of functioning properties for chronic pain
To reach a consensus regarding the FPs for chronic pain, the IASP and the ISPRM referred to the existing methodology for identifying relevant ICF domains.4,6,12 Subsequently, each society formulated a proposal for the FP for chronic pain.
The ISPRM considered the chronic widespread pain (CWP) core set to be the most comprehensive and relevant to generate FPs for chronic pain. Therefore, the comprehensive and brief core set for CWP was used. A discussion was held to reach a proposal of FPs by involving other experts, such as anesthesiologists, physical and rehabilitation medicine physicians, occupational therapists, physiotherapists (PT), and pain researchers.
The IASP developed the FPs for chronic pain from the generic set of the ICF. Then, further items that in pain experts' opinions (including anaesthesiologists, psychologists, neurologists, and general practitioners etc.) are relevant to chronic pain were added. The added items included sleep, cognitive functions, and self-care.
The 2 proposals (one by the ISPRM and one by the IASP) were discussed in a consensus meeting in Kuala Lumpur during the 10th ISPRM World Congress, on May 29, 2016. The meeting followed a workshop format and was attended by international experts, including physical and rehabilitation medicine physicians, anesthesiologist, PTs, occupational therapists, and pain researchers. A consensus was reached regarding the FPs for chronic pain.
The ICF already contains a core set for CWP, which is one of the most important chronic primary pain syndromes in the ICD-11.3 This core set identified 24 domains of body functions and structures (Table 2), 27 domains of activity and participation (Table 3), and 16 domains of environmental factors (Table 4) as relevant for patients with CWP.3 Assessment of all 67 domains by trained observers would be very time-consuming, hence a subset of these domains was selected as most relevant for CWP, which consists of 24 domains (brief core set, see Tables 2–4).3 The generic set of the ICF consists of 7 domains, 3 in body functions and structures including pain (Table 2) and 4 in activities and participation (Table 3). Initial conversations between representatives of ISPRM and IASP led to the conclusion that the generic set is insufficient for chronic pain because important domains are missing (eg, sleep), whereas the 2 sets for CWP were assumed to be too broad because they are designed to cover one of the most complex chronic primary pain syndromes. During the aforementioned consensus meeting in Kuala Lumpur, a list of 17 domains of FP was agreed. It contains 8 body functions, 7 activity and participation domains, and 2 environmental factors (Tables 2–4). The proposed set for chronic pain includes the following:
- (1) Three domains of body functions of the generic set:
energy and drive (b130), emotional functions (b152), and sensation of pain (b280)
- (2) Five additional domains of body functions:
sleep (b134), attention (b140), exercise tolerance (b455), mobility of joint (b710), and muscle power (b730).
- (3) Four domains of activities and participation from the generic set:
performing the daily routine (d230), walking (d450), moving around (d455), and remunerative employment (850)
- (3) Three additional domains of activities and participation:
Lifting and carrying objects (d430), intimate relationships (d770), and recreation and leisure (d920)
- (4) Two additional domains of environmental factors:
Individual attitudes of immediate family members (e410) and social security services, systems, and policies (e570)
This result was rediscussed within the IASP and within the ISPRM, with the understanding that a formal validation will be necessary before the final implementation. Although the pain codes in the ICD-11 have already undergone several field trials, none of them so far included the FPs as listed here. According to the reference guide of the WHO for the ICD-11,17 the FPs in the ICD-11 will only include the “activities” and “participation” domains (ICF code d—see also Table 3 in bold and italics):
- (1) Performing daily routine (d230)
- (2) Lifting and carrying objects (d430)
- (3) Walking (d450)
- (4) Moving around (d455)
- (5) Intimate relationships (d770)
- (6) Remunerative employment (d850)
- (7) Recreation and leisure (d920)
5. Discussion and outlook
For the treatment and rehabilitation of patients with chronic pain, it is of major importance to set up a clear diagnosis including the underlying pathology and the mechanisms of chronic pain. The distinction between chronic primary pain syndromes and chronic secondary pain syndromes will offer better integration with other branches of medicine when pain is predominantly the symptom of another disease (chronic secondary pain syndromes), while offering the lay public, and people with chronic pain among them, help in understanding what is wrong when chronic pain itself is the disease (chronic primary pain syndromes).15
For the patients themselves, other factors may play an equally important role in relation to suffering, QoL, and participation in family and other areas of social life. These factors are recorded as patient-reported outcome measures that become more and more important in evaluating the quality of health care. The multimodal pain management approach refers to a biopsychosocial model of pain that directs attention to these factors.5 Extension codes for chronic pain in ICD-11 cover a range of cognitive, behavioral, emotional, and social factors.15 The FPs of chronic pain in ICD-11 will primarily serve to code the social part of this model by cross-reference to the second major WHO classification: ICF.12
The ICF has a major focus on the patient's lived experience with high relevance for overall health, including (1) to understand the complex problems of patients with chronic pain, including psychological factors, the influence of the environment or behavioral stereotypes of the patients, and (2) focus on the patient experiences that are not only related to the symptoms, but the impact on daily life (which may require rehabilitation). The set of FPs for chronic pain presented here includes aspects of daily routines, mobility, and social interactions (partner, workplace, and recreation). This set was developed at the level of an expert consensus. Although it is based on results from the literature (ie, the ICF core sets for chronic pain and other pain conditions) and has a multiprofessional approach, its relevance must be validated. The chronic pain codes for the ICD-11 have been field tested on consecutive patient case series in 4 countries in 2016,1 and as part of the WHO validation of line coding and case coding in 2017, but functional properties were not part of those field tests. Future field tests should include aspects of feasibility and acceptance by users as well as the relevance for patients with chronic pain experiencing activity limitations and participation restrictions.
From a holistic point of view, a joint use of both classifications is recommended and will be facilitated by the integration of the ICF into the ICD-11. The integration of disease-specific strategies (so-called curative strategies) alongside a comprehensive approach to the QoL and functioning (so-called rehabilitation strategy) is crucial for an improved quality of care for patients suffering from chronic pain. The integration of the FPs into the new ICD-11 will be a great step forward to a holistic view on our patients and their needs for care (including multimodal pain management and rehabilitation). It will lead to an increased awareness of all health professionals regarding relevant problems the patients are struggling with. Thus, all stakeholders, including clinicians, patients, health insurers, and others will benefit from the inclusion of FPs.
On the other hand, there are also risks and problems occurring from the way FPs are included into the ICD-11. It has a reductionist approach by identifying the most frequent or most relevant domains of functioning. This ignores that activities and participation domains are highly individual and related to many individual and societal factors. Some of them are individual life goals, individual and societal attitudes, cultural background, religious, or other spiritual principles. They are also influenced by age, sex, assets, and position in society. For that reason, the assessment of the “most important” FPs must not replace the individual approach to identify the domains most relevant in the individual case.
Another limitation is the restriction of the ICD-11 functioning properties to “activities and participation” items from the ICF. One of the great achievements of the ICF is that it integrates body functions and structures, activities and participation, as well as the environmental and personal factors. For that reason, the integration of FPs (that represent only activities and participation) into the ICD-11 cannot replace the use of the ICF. For a comprehensive view of patients' problems, it is still necessary to refer to the definition of disability that is in line with the ICF. However, the extension codes for psychological and social factors in the ICD-11 and the pain severity code including pain intensity, distress, and disability add at least some information on nonsymptom determinants of disability in chronic pain.
This limitation also applies to the generic core set of the ICF, which-although it includes the sensation of pain, but as part of body functions-this is not going to be part of the FPs for all ICD-11 codes. Therefore, the chronic secondary pain syndrome codes developed by the IASP will be important as codiagnoses with an underlying disease, eg, diabetic polyneuropathy combined with chronic peripheral neuropathic pain. A further limitation derives from the differences in definitions of pain between the ICF and the IASP: the ICF places an emphasis on the sensory component of pain, whereas the affective motivational component included in the IASP definition may be more relevant in chronic pain patients. Furthermore, it is not fully obvious from the ICF definition that pain is defined (by the IASP) as a subjective percept, and anything that feels like pain is pain by definition, independent of any observable signs of nociception.14 In conclusion, the new codes for chronic primary and secondary pain syndromes in the ICD-11 are expected to improve diagnostic classification as indications for individualized pain management, and the integration of the ICF with the ICD is expected to further improve a holistic view of the patient including their functioning in everyday life.
Conflict of interest statement
A. Barke reports personal fees from IASP, during the conduct of the study. W. Rief reports grants from IASP, during the conduct of the study; personal fees from Heel, personal fees from Berlin Chemie, outside the submitted work. R.-D. Treede reports grants from Boehringer Ingelheim, Astellas, AbbVie, Bayer, personal fees from Astellas, Grünenthal, Bauerfeind, Hydra, Bayer, grants from EU, DFG, BMBF, outside the submitted work. The remaining authors have no conflict of interest to declare
The authors gratefully acknowledge the financial support by the International Association for the Study of Pain and the excellent discussions with Dr. Robert Jakob of the WHO. Members of the Taskforce: Rolf-Detlef Treede (Chair), Winfried Rief (Co-chair), Antonia Barke, Qasim Aziz, Michael I. Bennett, Rafael Benoliel, Milton Cohen, Stefan Evers, Nanna B. Finnerup, Michael First, Maria Adele Giamberardino, Stein Kaasa, Beatrice Korwisi, Eva Kosek, Patricia Lavand'homme, Michael Nicholas, Serge Perrot, Joachim Scholz, Stephan Schug, Blair H. Smith, Peter Svensson, Johannes Vlaeyen, Shuu-Jiun Wang.
Supplemental digital content
Supplemental digital content associated with this article can be found online at http://links.lww.com/PAIN/A658. SDC includes a complete reference list of the diagnoses entered into the foundation with the foundation IDs as well as the extension codes (specifier). Since the complete list is contained, the material is identical for all papers of the series.
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Classification; Chronic pain; ICF; Functioning; Core set; Disability; Rehabilitation
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