<h3>Background:</h3> Temporal artery biopsy (TAB) still represents the gold standard for giant cell arteritis (GCA) diagnosis. The eosinophilic infiltrate at TAB has been described in 8% of 274 TAB with transmural inflammation[1]. Whether it is part of the GCA spectrum or indicate other conditions is still controversial. <h3>Objectives:</h3> The aim of our study was to describe the clinical findings, disease course and treatment response of GCA patients with transmural eosinophilic infiltration at TAB. <h3>Methods:</h3> All biopsies with evidence of transmural inflammation obtained between January 1986 and December 2013 at the IRCCS in Reggio Emilia, Italy were reviewed by a single pathologist. The eosinophilic infiltrate was defined by ≥ 20 eosinophils/high-power-field (hpf) and was categorized according to the severity (mild ≥20 and &lt;40/hpf, moderate ≥40 and &lt;60/hpf, and severe ≥60/hpf). Patients with histological evidence of eosinophilic infiltration were compared with patients without for demographic, clinical and histological features. To compare the presence of eosinophil-related manifestations (namely asthma, allergic rhinitis, and nasal polyposis), patients with eosinophilic infiltrate were matched 1:2 for age, sex, and duration of follow-up (±5 years) with patients without. <h3>Results:</h3> 254 TAB were included, 22 (8.7%) showed evidence of eosinophilic infiltrate. GCA patients with eosinophilic infiltration were more likely females (p = 0.055). At diagnosis, they presented more frequently cranial symptoms (p = 0.052), particularly headache (p = 0.005), and systemic manifestations (p = 0.016). They also showed higher C-reactive protein levels at diagnosis (p = 0.001) (Table 1). Regarding histological lesions, a severe transmural inflammation, laminar necrosis, and intraluminal acute thrombosis were more frequently observed in patients with eosinophilic infiltration (p = 0.066, p &lt; 0.001, and p = 0.010, respectively). Almost no differences were observed in the two groups regarding frequencies of relapses, long-term remission, duration of glucocorticoid therapy and its cumulative dose. When the 22 patients were matched with 44 without eosinophilic infiltrate, no differences in the eosinophil levels or in the development of eosinophil-related manifestations were detected. Furthermore, no patient developed signs of systemic necrotizing vasculitis during follow up. <h3>Conclusion:</h3> Patients with transmural eosinophilic infiltration represent a subset of GCA patients with cranial manifestations and more severe inflammation, both at clinical and histological levels. <h3>REFERENCES:</h3> [1]Cavazza A,et al. Am J Surg Pathol. 2014 Oct;38(10):1360-70. doi: 10.1097/PAS.0000000000000244 <b>Table 1.</b> Demographic and clinical features at diagnosis of patient with eosinophilic infiltrate compared with those without. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>

POS0115 EOSINOPHILIC GIANT CELL ARTERITIS: A DIFFERENT SUBSET OF DISEASE?