Conventional Cancer Screening versus PET/CT in Dermatomyositis/Polymyositis

ObjectiveTo determine the value of whole-body [18F] fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for diagnosing occult malignant disease in patients with myositis compared with broad conventional cancer screening.MethodsWe prospectively studied 55 consecutive patients with a recent diagnosis of myositis in 3 teaching hospitals over a 3-year period by whole-body FDG-PET/CT and compared the results with those of conventional cancer screening, which included thoracoabdominal CT, mammography, gynecologic examination, ultrasonography, and tumor marker analysis. Comparisons were made using predictive values and their 95% confidence intervals.ResultsA total of 9 of 55 patients were diagnosed with paraneoplastic myositis. FDG uptake was positive in 7 patients (1 false-positive), negative in 44 patients (3 false-negative), and inconclusive in 4 patients. Positive and negative predictive values of FDG-PET/CT for the diagnosis of cancer were 85.7% and 93.8%, respectively. Conventional screening was cancer-positive in 9 patients (2 false-positive) and negative in the remaining 46 patients (2 false-negative). Positive and negative predictive values were 77.8% and 95.7%, respectively. The overall predictive value of broad conventional screening was the same as that of FDG-PET/CT (92.7 vs 92.7).ConclusionThe performance of FDG-PET/CT, a single imaging study, for diagnosing occult malignant disease in patients with myositis was comparable to that of broad conventional screening, which includes multiple tests.