Impact of multimorbidity on functioning: Evaluating the ICF Core Set approach in an empirical study of people with rheumatic diseases

Objective: Chronic conditions can lead to considerable deterioration in functioning. Several condition-specific Core Sets, selections of categories from the International Classification of Functioning, Disability and Health (ICF), have been developed to facilitate the rehabilitation process. Considering the increase in patients with more than one specific condition, we evaluated the impact of multimorbidity on functioning and the implications for the Core Set approach. Design: Internet survey. Subjects: A total of 127 people with a rheumatic disease and 707 people with rheumatic disease and multimorbidity were included. Methods: Self-report information on chronic conditions and perceived functioning using the IMPACT-S (ICF Measure of Participitation and Activities Screener) questionnaire, measuring the ICF component activities and participation (32 items). Results: The mean number of reported serious limitations/restrictions was 5.6 (standard deviation (SD) 5.7) for respondents with rheumatic disease and 6.7 (SD 6.8) for respondents with rheumatic disease and multimorbidity (p < 0.05). Seventeen items were relevant (more than 20% of the respondents reported serious limitations/restrictions) for individuals with rheumatic disease and multimorbidity, and 12 items were relevant for individuals with rheumatic disease only. Conclusion: Multimorbidity seriously aggravates the already existing functioning problems of people with rheumatic disease. We recommend that in the ICF Core Set approach more emphasis is given to systematic empirical analysis of the impact of multimorbidity on functioning.