Systemic vasculitis refers to a group of rare diseases characterized by inflammation of blood vessel walls, which may cause ischemia and structural damage in various organs. Among large-vessel vasculitides, Takayasu arteritis primarily affects the aorta and its main branches, whereas Behçet's disease is a variable vessel vasculitis involving arteries and veins of all sizes. Both conditions can lead to multisystemic involvement and significantly impact physical and psychosocial health.

This observational, case-control study aims to compare multiple physical and psychosocial parameters among individuals with Takayasu arteritis, Behçet's disease, and healthy controls. Assessments will include respiratory and peripheral muscle strength, functional status, exercise capacity, body composition, quality of life, illness perception, and psychological well-being. Measurements will be conducted using standardized clinical tests (such as maximal inspiratory and expiratory pressures, handgrip and limb strength dynamometry, squat test, and six-minute walk test) and validated questionnaires (Health Assessment Questionnaire (HAQ), the Short Form-36 Health Survey (SF-36), the EuroQol 5-Dimension 5-Level Questionnaire (EQ-5D-5L), and the Visual Analogue Scale (VAS)).

The study seeks to identify differences between groups and provide a comprehensive understanding of how systemic inflammation in Takayasu arteritis and Behçet's disease affects physical performance, quality of life, and psychosocial health. These findings may help guide physiotherapy, rehabilitation, and multidisciplinary management strategies for patients with systemic vasculitis.

Systemic vasculitis represents a heterogeneous group of rare inflammatory diseases that affect blood vessel walls, potentially leading to ischemia, tissue damage, and multi-organ dysfunction. Among them, Takayasu arteritis (TAK) and Behçet's disease (BD) are chronic, relapsing vasculitides characterized by systemic inflammation and variable vessel involvement. These diseases may cause not only organ-specific pathology but also generalized effects on muscle strength, physical function, and psychosocial well-being.

Previous studies have reported reduced physical performance, fatigue, and impaired quality of life in patients with systemic vasculitis. However, there is limited evidence directly comparing physical and psychosocial parameters between individuals with Takayasu arteritis, Behçet's disease, and healthy controls. The current literature lacks a comprehensive approach addressing the multidimensional impact of these diseases on functional and psychological outcomes.

This observational, cross-sectional study aims to fill this gap by evaluating and comparing respiratory and peripheral muscle strength, functional capacity, quality of life, illness perception, and related psychosocial parameters among these three groups. Measurements will include maximal inspiratory and expiratory pressures, handgrip and limb muscle strength via digital dynamometry, functional tests such as the squat test and the six-minute walk test, and standardized self-reported questionnaires including the Health Assessment Questionnaire (HAQ), the Short Form-36 Health Survey (SF-36), the EuroQol 5-Dimension 5-Level Questionnaire (EQ-5D-5L), and the Visual Analogue Scale (VAS).

The study is expected to provide a multidimensional understanding of how systemic inflammation in Takayasu arteritis and Behçet's disease affects physical and psychosocial functioning. The findings are anticipated to contribute to the literature by highlighting differences between disease groups and healthy controls and to guide future physiotherapy and rehabilitation strategies aimed at improving overall health and quality of life in individuals with systemic vasculitis.

Inclusion Criteria:

Inclusion Criteria (Takayasu Arteritis Group):

• Age 18 years or older.
• Diagnosis of Takayasu arteritis according to the American College of Rheumatology (ACR) classification criteria.
• Voluntary participation with written informed consent.

Inclusion Criteria (Behçet's Disease Group):

• Age 18 years or older.
• Diagnosis of Behçet's disease according to the International Study Group for Behçet's Disease criteria.
• Voluntary participation with written informed consent.

Inclusion Criteria (Healthy Control Group):

• Age 18 years or older.
• No history of systemic, rheumatologic, or chronic inflammatory disease.
• Voluntary participation with written informed consent.

Exclusion Criteria:

Exclusion Criteria (Patient Groups - Takayasu Arteritis and Behçet's Disease):

• Pregnancy.
• Presence of psychiatric disorder or ongoing psychiatric treatment.
• Cognitive impairment that may interfere with participation.
• Presence of neurological disease (e.g., hemiplegia, Parkinson's disease, multiple sclerosis, vertigo, epilepsy, etc.).
• History of any surgical operation within the past year.
• Coexisting rheumatic disease other than Takayasu arteritis or Behçet's disease.

Exclusion Criteria (Healthy Control Group):

• Pregnancy.
• Presence of psychiatric disorder or ongoing psychiatric treatment.
• Cognitive impairment that may interfere with participation.
• Presence of neurological disease (e.g., hemiplegia, Parkinson's disease, multiple sclerosis, vertigo, epilepsy, etc.).
• History of any surgical operation within the past year.
• History of rheumatologic or chronic inflammatory disease.

The study population will consist of individuals aged 18 years and older who have been diagnosed with Takayasu arteritis or Behçet's disease and are being followed at the Rheumatology Department of Pamukkale University, as well as age- and sex-matched healthy volunteers without systemic, neurological, or musculoskeletal disease. All participants will provide written informed consent prior to inclusion in the study.