Existing research on Takayasu arteritis has mainly focused on clinical, radiological, and immunological aspects, leaving a significant gap in understanding its functional, psychosocial, and multidimensional impact due to the absence of a disease-specific International Classification of Functioning, Disability, and Health (ICF) framework. This study aimed to analyze the problems of patients with Takayasu arteritis using a phenomenological approach based on the ICF.

A qualitative study was conducted with patients diagnosed with Takayasu arteritis. Eighteen patients were asked six open-ended questions. Their responses were audio-recorded and later transcribed. The responses were divided into meaningful units and linked to the most precise ICF categories by two independent health professionals. To evaluate the appropriateness of the linked ICF categories, sixteen rheumatologists were asked to indicate whether each category represented patients' problems, resources, or environmental aspects.

Patients' responses were linked to 122 ICF categories by the two health professionals, with a kappa coefficient of 0.774 indicating substantial agreement. Sixteen rheumatologists reviewed the linked categories through two rounds and a mini-Delphi process. Ultimately, 74 ICF categories were confirmed for the Takayasu arteritis Core Set with ≥75 % agreement. Forty-eight patient-identified categories were not confirmed by the rheumatologists (<75 % agreement).

The content validity of the ICF Core Set for Takayasu arteritis was supported by expert rheumatologists. This ICF Core Set can be applied to the evaluation of patients with Takayasu arteritis.