Diagnostic usefulness of fluorine-18-α-methyltyrosine positron emission tomography in combination with 18F-fluorodeoxyglucose in sarcoidosis patients

Objectives: L[3-F-18]-alpha-methyltyrosine (F-18-FMT) is an amino-acid tracer for positron emission tomography (PET) and is used for tumor detection because malignant tumor cells accumulate F-18-FMT based on the increased expression of an amino-acid transporter. This study was conducted to investigate the usefulness of F-18-FMT PET in combination with fluorine-18-fluorodeoxyglucose (F-18-FDG) PET for the diagnosis of sarcoidosis in patients with suspected malignancy. Setting: Twenty-four sarcoidosis patients with suspected malignancy underwent F-18-FDG and F-18-FMT PET. The study included 17 patients with extrapulmonary manifestation mimicking malignant disease (13 patients with systemic lymphadenopathy, 3 of them with concomitant hepatosplenic processes; 3 patients with hepatosplenic processes without concomitant lymphadenopathy; and I patient with multiple bone lesions), 3 patients with occurrence of bilateral hilar lymphadenopathy in cancer patients, and 4 patients with multiple nodules mimicking pulmonary metastasis. Results: All patients showed increased uptake of F-18-FDG and no increase in the accumulation of F-18-FMT in their lymphadenopathy. Standardized uptake values (SUVs) of F-18-FDG and F-18-FMT were 5.01 +/- 2.15 and 0.77 +/- 0.24, respectively (mean SD). All extranodal lesions such as liver, spleen, and boric were visually positive on F-18-FDG PET and negative on F-18-FMT PET. No neoplasm was confirmed in all patients. In a control group of patients with lung cancer, SUVs for F-18-FDG and F-18-FMT were 6.34 +/- 2.52 and 1.54 +/- 0.82, respectively. Conclusion: The uptake of F-18-FDG was positive in the sarcoid lesions, and therefore F-18-FDG PET could not differentiate sarcoidosis from malignant disease. Use of F-18-FMT PET in combination with F-18-FDG PET may be the effective method to distinguish sarcoidosis from malignancy.