THU0299 Understanding the heterogeneity of large-vessel vasculitides

Background Adult large-vessel vasculitides (LVV) are rare conditions, currently classified as two different diseases, Takayasu arteritis (TA) and giant cell arteritis (GCA), on an empirical basis. Insight into phenotypic and pathogenic differences between the two is scarce at best. Arterial involvement, despite being the central disease feature, has been poorly addressed by research. We have developed two novel, imaging-based scores (the arteritis stenosis score [ASS] and arteritis dilation score [ADS]). ASS and ADS define stenotic and aneurysmal disease in a core-set of 17 arteries and respectively represent the sum of stenosis and dilation scores in individual arteries1. Objectives To use ASS, ADS and the stenosis and dilation scores of individual arteries to describe a cohort of LVV patients and identify heterogeneity between patients. Methods The ASS, ADS and individual artery scores have been derived from 110 LVV (81 TA, 29 GCA) patients. Model-based clustering optimising the Bayesian Information Criterion and principal component analysis were performed. Results Arterial involvement was shown to be differed in GCA and TA: TA has higher ASS than GCA (median, IQR: 20, 11–29 Vs 5, 0–11; p We accounted for geographical distribution of lesions by evaluating the scores of individual arteries with correspondence analysis. Arterial involvement was symmetric with tripolar segregation: stenosis in the supra-aortic branches, stenosis in the aorto-abdominal district and arterial dilation (Fig 1A). When patients exhibited the first two components, three different clusters were recognised (Fig 1B), with different ASS, ADS and damage as assessed by the TA damage score (p Conclusions Arterial involvement differs in TA and GCA, although some overlap exists. Elderly TA is similar to juvenile TA, while a potential biologic “switch”, yet to be identified, regulating the final outcome of arterial remodelling and influenced by ageing, is present in GCA. Three main patterns of arterial involvement appear to exist. LVVs represent the composition of different discrete subsets rather than a phenotypic continuum. References : Tombetti et al. EULAR 2015 Poster FRI0258. Disclosure of Interest None declared