Distinct Clinical Outcomes of Positron Emission Tomography/computed Tomography-Based Subtypes in Treatment-Naïve Takayasu Arteritis.

OBJECTIVE:Positron emission tomography/computed tomography (PET/CT) enables the visualization of vascular inflammation in Takayasu arteritis (TAK). However, the prognostic significance of PET/CT-based arterial involvement remains unclear. This study aimed to classify the distribution patterns of vascular lesions in treatment-naïve TAK using PET/CT and evaluate their association with clinical outcomes. METHOD:Patients with TAK who underwent PET/CT before treatment initiation were retrospectively analysed. Hierarchical clustering was performed based on the distribution of arterial 18F-fluorodeoxyglucose uptake. The clinical outcomes, including relapse and large-vessel complications, were analysed according to the resulting clusters using survival analyses. Longitudinal changes in PET/CT findings and clinical activity were assessed. RESULTS:Thirty patients (90% women) were included, with a median follow-up of 4.8 years and median age at diagnosis of 48 years. Three distinct PET/CT-based clusters were identified: thoracic (43%), diffuse (30%), and localized (27%). The diffuse type showed the highest relapse rate 24.1/100 person-years, p = 0.04), whereas the thoracic type tended to be associated with more vascular complications (13.9/100 person-years, p = 0.12). The Numano classification did not always correspond to PET/CT-based clusters or predict clinical outcomes. A PET Vascular Activity Score ≥ 7 was associated with relapse but not with vascular complications. PET/CT activity persisted despite clinical inactivity in some cases, which may cause future relapse. CONCLUSION:PET/CT-based classification suggested three distinct TAK subtypes with different clinical outcomes. The diffuse type was significantly associated with relapse, whereas the thoracic type caused vascular complications. PET/CT provided superior risk stratification compared to the conventional classification.