The objective of this study is to identify similarities and differences in functioning in AS and RA using the ICF as the framework for the description of functioning.
The Comprehensive ICF Core Sets for RA and AS were compared qualitatively regarding their content. A comparison study of common second-level ICF categories from both ICF Core Sets collected in two different cross-sectional studies in the Netherlands was performed. Significant differences regarding the level of impairments, limitations or restrictions were analyzed within the Mann-Whitney U-Test. To study whether the common ICF categories have different meaning for the two populations the Rasch model for dichotomous response option was used.
The Comprehensive ICF Core Set for AS includes 74 ICF categories in 19 chapters and the Comprehensive ICF Core Set for RA includes 96 ICF categories in 22 chapters. Interviews among 87 patients with AS and 143 patients with RA on 24 of the common ICF categories revealed significant differences regarding the extent of problems. DIF analyses reflect that the meaning of some ICF categories, such as 'd410 Changing basic body positions' is different in relation to functioning depending on the health condition.
This study was the first to compare functioning in AS and RA based on the ICF. The results confirmed to a large extend the experiences well known from other studies and thereby showed that the ICF is useful to describe and compare functioning. Some aspects could be identified which are not easy to understand with existing evidence and need to be explained in the future.