SAT0536 DIAGNOSTIC UTILITY OF POSITRON EMISSION TOMOGRAPHY FOR THE EVALUATION OF PATIENTS WITH INFLAMMATION OF UNKNOWN ORIGIN

Background Underlying causes of inflammation cannot be established sometimes, despite meticulous medical history and physical examination, laboratory tests including cultures, immunologic and serologic tests and widely used radiologic procedures such as plain x-rays, echocardiography, ultrasonography and computed tomography. Rheumatologists quite oftenly face with these patients which is termed as inflammation of unknown origin (UIO). Differential diagnosis of UIO is diverse and investigation of such cases are challenging and time consuming. Objectives: to assess diagnostic utility of PET CT in the diagnosis of patients with UIO Methods Study comprised 68 (36 male, mean age 58.7±14.8, range 19-87 years) adult IUO subjects without a previous diagnosis of an inflammatory or malignant disease. Patients were screened with PET CT after 8 hours fasting, if a specific diagnosis could not be established with comprehensive evaluation including; meticulous history and physical examination, pertinent microbiologic cultures, brucella agglutination, Mantoux test, serum protein electrophoresis, echocardiography, plain x-rays, computed tomography of thorax and abdomen/pelvis. Results Final diagnosis were established in follow up were inflammatory diseases in 37 (54.4%), malignant disorders in 16 (23.5%) and infections in 5 (7.4%), whereas a final diagnosis cannot be made in 10 (14.7%). PET CT aided diagnosis in 40 (58.8%) patients but was ineffective in 28 (41.2%). All three PET CT positive subjects with a final diagnosis of infection had tuberculosis (tb). On of two PET negative subjects had EBV and one other also had tb. PET CT was positive in 24 of 37 (64.9%) subjects with a final diagnosis of inflammatory rheumatic disease. Final inflammatory diseases were large vessel vasculitis 15, polymyalgia rheumatica 5, seronegative arthritis 4, and other rare miscellaneous diseases, such as small vessel vasculitis, inflammatory myositis, polychondritis, sarcoidosis and IgG4 related disease. PET was positive in 11 of 15 (73.3%) large vessel vasculitis patients and 2 of 5 (40%) PMR patients. Because of small number of miscellaneous rheumatic diseases, diagnostic value of PET cannot be evaluated in these. Conclusion Investigation of underlying etiology of UIO is time and effort consuming. PET CT may help to identify final diagnosis more quickly by directing an obscure inflammatory site. PET CT may also have advantages like reducing number of unnecessary biopsies, diagnostic time, anxiety, work loss, morbidity and mortality References [1] Kan Y, Wang W, Liu J, Yang J, Wang Z. Contribution of 18F-FDG PET/CT in a case-mix of fever of unknown origin and inflammation of unknown origin: a meta-analysis. Acta Radiologica. 2018:0284185118799512. Disclosure of Interests None declared