Clinical usefulness of 18F-FDG PET/CT for detecting malignancy in patients with autoimmune disease

Objectives Individuals with autoimmune disease have an increased susceptibility to certain types of cancer. The aim of this study was to evaluate the usefulness of 18F-FDG PET/CT for detecting malignancy in patients with autoimmune disease.

Methods Thirty-one patients (F: 24, M: 7, mean age: 50 ± 12 years) with autoimmune disease (9 with systemic lupus erythematosus, 8 with dermatomyositis/polymyositis, 5 with rheumatoid arthritis, 4 with adult-onset Still's disease, 4 with Sjögren’s disease, and 1 with polymyalgia rheumatic) were referred for 18F-FDG PET/CT to evaluate suspected internal malignancy. 18F-FDG PET/CT results were compared with histopathologic examination (n=16, 52%) and clinical outcome (n=15, 48%) as reference standard.

Results The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of PET/CT for the detection of malignancy were 100%, 67%, 71%, 31% and 100%, respectively. One-hundred percent (4/4) of patients were successfully diagnosed with malignancy (2: B-cell lymphoma, 2: primary lung cancer). In 33% (9/27) of the patients without malignancy, false-positive results were found in 6 patients with reactive lymphadenitis (LAP), 2 patients with tuberculous LAP and 1 patient with disseminated breast tuberculosis. The maximum standardized uptake value of LAP was 10.5 ± 7.2 (mean ± SD) in lymphoma, and 9.1 ± 4.3 in reactive LAP, and 16.6 ± 5.1 in tuberculous LAP. Spleen (75%) and joint (75%) involvements without extralymphatic organ invasion (0%) are frequent findings in reactive disease.

Conclusions Our preliminary data shows that 18F-FDG PET/CT is useful as a primary tool in detecting malignancy in patients with autoimmune disease. However, frequent reactive changes associated with/without infection can lead to false-positive results on PET/CT in the patients with autoimmune disease