Background The interpretation of data from 18F-FDG PET/CT studies on large vessel vasculitis (LVV) is difficult due to the scarcity of studies and to the heterogeneity of LVV populations examined. In the absence of gold standard parameters for the assessment of LVV arterial inflammation, there is a great need to develop analytical methodologies useful to properly exploit the information derived from such studies. Principal component analysis (PCA) and cluster analysis (CA) have not yet been applied to explore the LVV distribution patterns, assessed by 18F-FDG PET/CT.
Objectives The aim of our study was to investigate whether PCA and CA are useful methods in identifying distinct distribution patterns of LVV, according to the specific diagnostic entity examined (giant cell arteritis, GCA; Takayasu's arteritis, TAK).
Methods A total of 130 18F-FDG PET/CT studies have been retrospectively examined by a nuclear physician blinded to clinical data. Maximum standardized uptake values (SUVmax) in 14 vascular districts including aortic segments (ascending aorta, thoracic aorta, aortic arch, discending thoracic aorta and abdominal aorta) and the main tributaries (carotid, subclavian, axillary, iliac and femoral arteries) have been measured and transformed into Z-scores. Identification of distribution patterns of vascular involvement has been performed using PCA and agglomerative hierarchical CA (SPSS Statistics, version 22nd).
Results Three groups of vascular districts with similar trends in terms of standardized SUVmax have been identified: epiaortic arteries; aortic arch and ascending aorta; descending and abdominal aorta, with iliac and femoral arteries. A component including the entire aortic district was identified in TAK group, but not in GCA group.
Conclusions PCA and CA approach revealed a subtle skewing in terms of distribution patterns of arterial involvement between TAK and GCA, assessed by 18F-FDG PET/CT SUVmax values. The influence of atherosclerosis and immunosenescence on the different trends in the aorta districts of TAK and GCA needs to be further elucidated.
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Disclosure of Interest None declared