Validation of the International Classification of Functioning, Disability and Health Core Set for chronic widespread pain from the perspective of fibromyalgia patients

The perspective of functioning, disability and health of the World Health Organization [1] establishes the basis for a comprehensive description of the experience of patients suffering from a determined disease. This perspective recognizes different aspects of health from a biological, individual and social perspective, providing for a coherent view of illness [2]. This holistic approach guided the development of the International Classification of Functioning, Disability and Health (ICF), which was approved by the World Health Assembly in May 2001. Since the ICF has been developed in a worldwide, comprehensive process and was endorsed by the World Health Assembly as a member of the World Health Organization Family of International Classifications, it is likely to become the generally accepted framework to describe functioning, disability and health from a bio-psycho-social perspective.

Based on the bio-psycho-social perspective, the ICF classification contains the so-called ICF components Body Functions, Body Structures and Activities and Participation as well as the contextual factors Environmental and Personal Factors (see Figure 1). Both functioning and disability represent the result of the interaction between Body Functions, Body Structures and Activities and Participation of an individual with a health condition and the contextual factors of that individual. The ICF classification contains more than 1,400 so-called ICF categories, each allotted to the named components of the classification – with the exception of the component Personal Factors, which has not yet been classified. Each ICF category is denoted by a code composed of a letter that refers to the components of the classification (b, Body Functions; s, Body Structures; d, Activities and Participation; and e, Environmental Factors) and is followed by a numeric code starting with the chapter number (one digit), followed by the second level (two digits) and the third and fourth levels (one digit each) (see Figure 1).

To address the issue of feasibility regarding the over 1,400 ICF categories, ICF Core Sets have been developed in a formal-decision-making and consensus-based process integrating evidence gathered from preparatory studies for a number of most burdensome, chronic health conditions. ICF Core Sets represent a selection of ICF categories out of the whole classification that can serve as minimal standards for the reporting of functioning and environmental factors for clinical studies and clinical encounters (Brief ICF Core Set) or as standards for multiprofessional, comprehensive assessment (Comprehensive ICF Core Set). Since the ICF Core Sets address aspects within all of the components of the ICF (Body Functions, Body Structures, Activities and Participation, Environmental Factors) they present a broad perspective that may reflect the whole health experience of patients.

One of the several health conditions for which ICF Core Sets were developed is chronic widespread pain (CWP). A common musculoskeletal disorder, CWP is characterized by generalized muscular pain and tenderness at multiple sites. Clinical examinations reveal no disease in joints and muscles. Fibromyalgia (FM) is one of the most severe clinical manifestations of CWP. According to the American College of Rheumatology, patients with widespread pain for at least 3 months and tenderness in 11 out of 18 tender points on digital palpation are classified as suffering FM [3]. In addition to pain, FM is characterized by fatigue, sleeping problems, mood disorder and several other symptoms as well [4]. An estimated 0.5 to 4% of the population suffers from FM [5]. Working, managing daily tasks and functioning in general can become a tremendous burden for the sufferers. Functioning represents the core of the patients' experience and is determined and influenced by their interaction with the environment and their own personal characteristics – not only by the health condition [6‐9]. This is reflected by patients themselves and also by health professionals treating patients with FM. Owing to the multidimensional nature of FM, however, experts in general have recognized the difficulty of finding standardized measures, thus limiting the progress in therapeutic approaches.

The lack of standardized or validated outcome measures for FM has caused uncertainty regarding which key domains of the condition should be measured. This has been acknowledged by initiatives such as the Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT), the goal being to define what should be measured and how, across the spectrum of rheumatology intervention and observational studies [10]. OMERACT FM workshops have been held with the objective of standardizing and improving the quality of outcome research in FM by identifying and prioritizing domains [11, 12]. The ICF can help specify OMERACT domains by serving as a conceptual model to define functioning.

The Comprehensive ICF Core Set for CWP describes the typical spectrum of problems in functioning among patients with CWP. Additionally, it provides an ideal basis from which to define theoretically sound models of functioning and disability in patients with CWP. The current version of the Comprehensive ICF Core Set for CWP includes 65 ICF categories at the second level and two ICF categories at the third level of the classification.

Qualitative methodology provides the possibility of exploring the perspective of those who experience a health problem; that is, the patient perspective [13, 14]. Qualitative methods, especially focus groups, are now widely used and increasingly accepted in health research and health-related sciences [15‐17]. The idea behind the focus group methodology is that group processes can help people explore and clarify their views [18]. The nondirective nature of focus groups allows participants to comment, explain, disagree and share experiences and attitudes [19]. The Comprehensive ICF Core Set for rheumatoid arthritis was validated recently from the patient perspective using qualitative methodology. Seventy-one out of the 76 ICF categories in this ICF Core Set were confirmed, and an additional 57 categories not covered in the ICF Core Set for rheumatoid arthritis were found [20]. Further studies for validation of ICF Core Sets from the patient perspective are currently in progress, including those for stroke, low-back pain and diabetes.

The objective of the present study was to add evidence to the validation of the Comprehensive ICF Core Set for CWP from the perspective of patients with FM. The specific aims were to explore the aspects of functioning and health important to patients with FM using focus group methodology and to examine to what extent these aspects are represented by the current version of the Comprehensive ICF Core Set for CWP.

Most ICF categories of the current version of the Comprehensive ICF Core Set for CWP could be confirmed from the patient perspective by FM patients. Fifty-four ICF categories out of 67 categories of the Comprehensive ICF Core Set for CWP were reported by the patients. Forty-eight additional categories that are not covered in the Comprehensive ICF Core Set for CWP were raised. The present study also confirmed relevant outcomes of treatment in CWP and FM from the patient perspective, such as pain, fatigue, sleep disorders, psychological distress, lack of muscle power, difficulties changing and maintaining a body position, and difficulties carrying out a daily routine [29, 30]. Pain proved to be the central topic reported by patients, with a total of 159 concepts linked to the ICF Core Set category sensation of pain (b280).

Apart from pain, the most outstanding theme reported by participants was the attitude of others regarding FM. The patients describe often feeling left alone with their illness, due to a lack of understanding and acceptance from others. Several patients reported feeling as if FM is not accepted as a legitimate illness by some doctors and healthcare professionals and is often trivialized by friends, relatives and colleagues, thus adding to the burden of pain and exhaustion. Fifty-five concepts concerning negative attitudes of others regarding the illness were linked to the corresponding ICF Core Set categories (e410, e420, e425, e430, e450, e455). Forty-six additional concepts were linked to the first-level ICF category attitudes (e4). Several studies report similar findings such as patients' experiences of stigma [31‐34] and studies documenting controversy as to the existence, classification and acceptance of FM by healthcare professionals [35‐38].

Thirteen ICF categories in the Comprehensive ICF Core Set for CWP were not at all mentioned by the focus groups. Most of the ICF categories belonged to Body Functions and included global psychosocial functions (b122), psychomotor function (b147), content of thought (b1602), proprioceptive function (b260) and haematological system functions (b430). Some categories were not confirmed but were linked to similar categories; for example, 18 concepts were linked to the category carrying out daily routine (d230) instead of undertaking multiple tasks (d220), and nine concepts were linked to intimate relationships (d770) instead of sexual functions (b640). Sometimes the participants made more specific statements that were linked to similar ICF categories; for example, although the ICF Core Set category societal attitudes (e460) was not linked, several statements were linked to categories e410 through e455 specifying individual attitudes (for example, individual attitudes of friends, colleagues, people in positions of authority, health professionals).

Forty-eight additional second-level ICF categories that are not covered in the current version of the Comprehensive ICF Core Set for CWP were raised. Most of the additional ICF categories belong to Body Functions, followed by Activities and Participation and Environmental Factors. Some of these additional ICF categories need special discussion. Several concepts deal with difficulties in cognitive functioning. Thirty-two concepts were linked to the Body Functions category memory functions (b144). The patients reported problems with short-term and long-term memory such as absorbing, storing and recalling information. Learning and applying knowledge was also perceived as challenging for the participants. Difficulties acquiring skills, thinking, hearing, listening and reading were frequently reported by the focus group participants. Poor memory performance and problems in cognitive functioning in FM sufferers have been well documented and are in accordance with other studies [39‐42]. Sensations associated with hearing, such as tinnitus and dizziness, were also reported by the participants, as in other studies [43, 44].

The use of the hands and arms is a further topic not included in the Comprehensive ICF Core Set for CWP that FM sufferers experience as very burdening. The participants reported difficulties in grasping, picking up and manipulating objects with their hands and pulling, reaching and turning or twisting the arms, making everyday activities and tasks very difficult to fulfil. Twenty-seven and 15 concepts were linked to fine hand use (d440) and hand and arm use (d445), respectively.

An additional topic found among the participants but not included in the Comprehensive ICF Core Set for CWP was functions of the digestive system. Such problems included difficulties with salivation, swallowing and digesting food. Urinal and intestinal irregularities were frequently reported and experienced as extremely hindering, affecting numerous activities and participation in sports and social engagements. Irritable bowel syndrome and urinary problems in FM sufferers are reported in other studies as well [45‐47]. Twenty-two concepts were linked to functions related to the digestive system (b510 to b535). Some participants mentioned feeling as if fingers, hands, feet or legs were swollen although swelling was not always visible. These concepts were labelled not definable. Other topics concerned Environmental Factors not covered in the ICF classification (labelled not covered). Numerous patients mentioned the benefits of heat, such as using hot or warm water to sooth aching body parts. Several others recognized the importance of exercise in coping with pain and fatigue.

The characteristics of the sample in this study (gender, age, disease duration) are comparable with samples in other national [48] and international studies [49]. The validation of the ICF Core Set for rheumatoid arthritis from the patient perspective using the same approach as in the present study showed similar results. Seventy-one out of the 76 ICF categories in the ICF Core Set for Rheumatoid Arthritis were confirmed and an additional 57 categories not covered in the ICF Core Set for rheumatoid arthritis emerged [20].

It is important to mention that several strategies were used to improve and verify the trustworthiness of the data analysis. Triangulationensured the comprehensiveness of data; we included data triangulation by using two data analysts (investigator triangulation: multiple coding) [50, 51]. Secondly, reflexivity was assured by conducting a research diary for the documentation of memos concerning the design, data collection and data analysis. Clear exposition was also used, establishing guidelines for conducting the focus groups (including open-ended questions), verbatim transcription, and linking rules [28]. Finally, peer review was included, as described earlier. The kappa coefficient of 0.76 (0.70 to 0.82) for the accuracy of the peer review is comparable with other studies reporting kappa statistics about the linking of categories [22, 52, 53], and can be regarded as substantial agreement.

There are some limitations of the present study that need special mention. The sample consists primarily of German residents. To establish a cross-cultural perspective we suggest that our methods be used in similar studies in other countries. Second, FM is a subtype of CWP, and may not be representative of all CWP conditions. Other ICF categories may have emerged if focus groups had been conducted with other CWP illnesses such as chronic fatigue or Gulf War syndrome. The controversy concerning the existence, classification and acceptance of FM interferes with the patients' need to be recognized and taken seriously with their illness. This may exacerbate symptoms and add to the burden of pain and exhaustion. Third, the linking process was performed by two psychologists according to established linking rules [28]. Whether other health professionals would have decided differently, however, remains unclear. Finally, we conducted six focus groups following the strategy of saturation during data analyses, with the criteria of two consecutive focus groups each revealing less than 5% additional ICF categories in relation to the number of ICF categories of the Comprehensive ICF Core Set for CWP identified in the respective previous focus group. Participants in a seventh focus group might still report new themes and concepts not yet addressed.

The results of the present study are comparable with the results of the validation of ICF Core Sets for rheumatoid arthritis. In line with the validation study of ICF Core Sets for CWP, most of the ICF categories included in the ICF Core Set for rheumatoid arthritis were also confirmed [20]. In addition, both studies identified numerous ICF categories from the patient perspective that were not included in the current versions of the ICF Core Set. All results of the validation studies of ICF Core Sets will be presented at an international World Health Organization conference and will be taken into account for the decision on the final versions of ICF Core Sets.

It is important to consider the patient perspective for the validation of the Comprehensive ICF Core Set for CWP. Most ICF categories of the existing version of the Comprehensive ICF Core Set for CWP could be confirmed by focus groups with FM patients. Several additional categories not represented in the Comprehensive ICF Core Set for CWP emerged from the focus groups and should be considered for inclusion in the final version.