Background:Giant cell arteritis (GCA) represents the most common primary vasculitis of the elderly, that usually involves large and medium sized arteries. The wide spectrum of clinical manifestations can extensively vary, from cranial symptoms, such as headache, jaw claudication or visual alterations, to constitutional symptoms, like fever, weight loss or asthenia. Fever of unknown origin (FUO) may sometimes represents the initial symptom of GCA and when it is not associated with other typical GCA features, the diagnosis can be unluckily delayed.Objectives:The primary aim of the study was to identify the prevalence of GCA patients presenting as FUO. The secondary aims were to identify the delays in the diagnosis and to compare them between the last two decades.Methods:Epidemiological and clinical data of 274 GCA patients followed in the last 20 years in our Unit were analysed. We quantified the latency period between the onset of signs and symptoms and the final diagnosis of GCA in terms of months.Results:One hundred and eighty-five patients (49 males and 136 females, mean ± SD age at the onset 71±7 years) had shown at the onset signs and symptoms suggestive of GCA (new onset headache and/or scalp pain 86%, jaw claudication 39%, vision loss 35%, abnormal temporal artery on examination 49%, dizziness 31%) while 89 patients (33 males and 56 females, mean age at the onset 69±4 years) were sent to our attention just for the onset of FUO and for an increase of erythrocyte sedimentation rate and C-reactive protein not otherwise justified. After an extensive work-up aimed at excluding any kind of infection, malignancy or hematological disorder, the patients with FUO performed a temporal artery biopsy (TAB) and/or a (18)F-fluorodeoxyglucose positron emission tomography (18F-FDG PET). The results from histology and/or imaging allowed us to perform the diagnosis of GCA in all cases; moreover the main PET alterations reported were characterized by a (18)FDG uptake of the aortic arch and its major braches, including the carotid, subclavian, thoracic aorta and, less frequently, the abdominal aorta. Considering the different decades, the mean latency period between the onset of FUO and the diagnosis of GCA was 6±3 months in the decade from 2000 to 2010 and 3±2 months in the last decade, that was significantly higher compared with the mean latency period between the onset of signs and symptoms suggestive of GCA and the definitive diagnosis (3±1 months) in the other patients of the cohort in the first decade. Notably the latency period between the onset of signs and symptoms suggestive of GCA and the definitive diagnosis was more close (2±1 months) to the latency period of diagnosis in FUO presenting GCA in the last decade.Conclusion:Our data underline that there is a major focus on the diagnosis of GCA, even when the presentation is not typical; this is probably due to the major knowledge reached in the last decade, to an improved sensibilization regarding the different profiles of presentation and surely on the bigger use of 18F-FDG PET in the work-up of GCA patients.Acknowledgments:noneDisclosure of Interests:None declared