Sarcoidosis (SA) is a disease involving abnormal collections of inflammatory cells that can form as granulomas in multiple organs. It has a variable natural course from an asymptomatic state to a progressive disease. Management of SA is complex due to the disease’s variable natural history and response to treatment and there are also no clear objective indicators for predicting prognosis. Currently, in standard clinical practice, a combination of clinical, functional and imaging criteria is used in relapsing or progressive disease, leading to significant differences in initiation and duration of treatment. 18F-FDG PET has proved to be a sensitive technique in the assessment of disease activity. However the routine use of 18F-FDG PET in the management of SA is not validated yet. The aim of the present study is to determine whether or not 18F-FDG PET is useful in guiding treatment in patients with SA.
Thirteen patients (8 males and 5 females; median age: 51 years; range: 31-72 years) with chronic histopathologically proven SA who performed 18F-FDG PET from 2007 to 2013 to evaluate disease extension before starting therapy were retrospectively included in the study. Eleven/13 patients started treatment (prednisone and/or methotrexate) based on the presence of active lung parenchymal inflammation and/or lymph-node pathological uptake as assessed by 18F-FDG PET (8/13) or because of clinical symptoms (3/13). The remaining patients (2/13) did not perform any treatment. All 13 patients were studied with 18F-FDG also during follow-up (mean 41 months; range: 10-77 months) with a total of 41 follow-up scans. To evaluate the treatment response, the most recent 18F-FDG PET during follow-up was considered and compared with the basal scan. Treatment was reduced/discontinued if follow-up PET documented a complete metabolic response. All pulmonary and lymph-nodal PET positive findings were evaluated using both qualitative (visual examination) and semi-quantitative methods (SUVmax; MTV; TLG).
All 13 patients showed positive findings at basal PET. Specifically, 8/13 (62%) presented lung (mean SUVmax=9; mean MTV=36; mean TLG=177) and lymph-node pathological uptake (mean SUVmax=13; MTV=33; TLG=358). Of these, 2 also presented a previously unknown bone involvement. Five/13 (38%) patients presented pathological 18F-FDG PET uptake only at lymph-node level (mean SUVmax =11; mean MTV=35; mean TLG=235). In 4/11 (36%) treated patients, PET documented a complete metabolic response and the treatment was reduced/discontinued during follow-up. For the remaining 7/11 (64%), PET documented partial metabolic response (n=1), stable activity (n=3) or progression of active inflammation (n=3) and so the treatment was carried on.
18F-FDG PET could be a useful tool for the evaluation of activity and extension of SA, being also of help in clinical management for starting/modifying treatment as based on the presence/absence of active inflammation and on the detection of previously unknown lesions.

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