Linking the patient experience of foot involvement related to psoriatic arthritis to the International Classification of Functioning, Disability and Health

Background: Previous research has shown merit in linking domains of impact in psoriatic arthritis (PsA) to the International Classification of Functioning, Disability and Health (ICF) to categorise the effect of global disease [1, 2]. Localised disease predominance and persistence in the foot in PsA is well recognised [3], but limited foot-specific research exists and there are no outcome measures to comprehensively assess foot involvement and its impact in PsA. To date little is known about the patient experience of foot involvement and how this may link to the ICF to capture disease impact. Objectives: To categorise the patient experience of PsA-related foot problems by linking it to the ICF. Methods: Participants were recruited from rheumatology outpatient clinics in Sydney, Australia and Auckland, New Zealand. People with PsA were interviewed about their foot problems and the impact they have on daily living until qualitative data saturation. Three multi-disciplinary focus groups were undertaken with clinicians to explore their understanding of the patient experience. All interviews were audio-recorded and transcribed. Codes, representing concepts obtained from the interviews, were linked to the most appropriate ICF category according to established linking rules. All codes were independently linked to the ICF by 2 investigators and a third investigator for adjudication. Investigator professional backgrounds included occupational therapy and podiatry. Results: Twenty-one people with PsA-related foot problems and 17 experienced clinicians participated. Over 100 distinct ICF categories were linked to the interview and focus group codes. The most represented ICF category was environmental factors (33%) followed by body functions (26%), activities and participation (25%) and body structure (16%). Environmental factors relevant to patients were shoes and assistive devices, healthcare access and climate. Clinicians identified a greater proportion of body functions and fewer activity and participation categories compared with patients, indicating a possible mismatch of key concerns. Concepts that could not be precisely linked to the ICF were related to coping, aspects of time and knowledge, consistent with previous work. Difficulties in linking highly specific information to categories such as sensations of pain, sensations of skin and emotional functions revealed a limitation in the ICFs ability to discriminate between various effects of the disease, a shortfall previously noted. Toenail changes were frequently cited by patients and linked to domains of body image and social relationships. Interdisciplinary group analysis demonstrated merit as differences between the predominantly medical approach by podiatry and psychosocial approach by occupational therapist in clinical practice led to additional ICF categories being identified between clinicians, which mostly related to cognitive functions. Conclusion: Despite the localised anatomical focus of this study, the effect of foot problems in PsA was linked to all components of the ICF, confirming the profound impact on functioning and daily life. Difficulties with linking psychological concepts reflect deficiencies in the ICF and is a major limitation in defining foot disease burden. These findings offer new knowledge using patient and clinician perspectives that could inform the development of an instrument to measure the impact of foot involvement in PsA.