This is a multicenter prospective observational study aimed at evaluating the role of an ultrasonographic score in monitoring disease activity in patients with Takayasu arteritis (TAK). Patients with active disease, either at new diagnosis or during relapse, will undergo serial vascular US assessments during follow-up according to routine clinical practice at each participating centers. For each patient, an OMERACT-derived US score (OTUS) will be calculated. This score was developed and preliminarily validated in previous phases of a multistep project endorsed by OMERACT (Outcome Measures in Rheumatology), an international initiative focused on the development and validation of outcome measures in rheumatology. The study hypothesis is that this score is sensitive to change over time and can be used to monitor disease activity and predict outcome in patients with TAK.

This is an observational study. The study concerns a diagnostic procedure (vascular US) that is part of normal clinical practice for patients with large-vessel vasculitis (LVV). The decision to perform vascular US in patients with TAK will remain independent from the decision to enroll the patient in the study. No investigational medicinal product or experimental device is involved. The procedure under study is an ultrasonographic scoring system derived from vascular US examinations of selected arterial segments in patients with TAK. Examinations will be performed according to standardized OMERACT protocols, including assessment of the common carotid, subclavian and axillary arteries, and the abdominal aorta. For each patient, an OMERACT-derived OTUS score will be calculated at each assessment. No comparator is mandated; however, clinical disease activity state and results from other imaging modalities (FDG-PET, MRA, CTA), when available as part of routine clinical care, will be collected for exploratory analyses. Study participation will last 24 months, during which patients will undergo serial US examinations at predefined follow-up visits as part of routine clinical monitoring. Vascular US is a non-invasive, radiation-free and contrast-free technique, already employed in standard clinical care and used here exclusively for observational purposes.

Inclusion Criteria:

• Age ≥18 years

• Male and female

• Diagnosis of TAK according to the 1990 ACR and/or 2022 ACR/EULAR classification criteria

• Active disease, defined as the presence of at least two of the following three domains:

  • Clinical domain: new onset or worsening of clinical signs and/or symptoms attributable to TAK;
  • Laboratory domain: elevation of inflammatory markers, defined as ESR and/or CRP above the upper limit of normal according to local laboratory standards, not attributable to causes other than TAK;
  • Imaging domain: imaging evidence of active vasculitis on modalities other than ultrasound, including FDG-PET, magnetic resonance angiography (MRA), or computed tomography angiography (CTA).

• Ability to undergo serial vascular ultrasound assessments during follow-up

• Provision of signed informed consent

Exclusion Criteria:

• Inability or contraindication to undergo vascular US
• Severe comorbidities limiting participation or follow-up
• Concomitant conditions that may confound ultrasound findings (e.g., significant atherosclerosis requiring intervention, complete occlusion of one of the arterial segments under investigation)
• Diagnosis of another rheumatologic disease
• Refusal or inability to provide informed consent

The study population will consist of patients with TAK and active disease, either newly diagnosed or experiencing a relapse. Active disease is defined as the presence of clinical signs and/or symptoms attributable to TAK, with or without elevation of inflammatory markers (ESR, CRP), and/or imaging evidence of active vasculitis (excluding US findings used in OTUS scoring).

Patients of any gender, aged ≥18 years, will be eligible.