False-positive FDG positron emission tomography in pulmonary amyloidosis

Positron emission tomography (PET) using F-18 fluorodeoxyglucose (FDG) is frequently used to characterize solitary pulmonary nodules suspected of being malignant. However, increased FDG activity in benign pulmonary nodules is not uncommon and can be seen with active granulomatous disease (tuberculosis, fungal infections, and sarcoidosis) and inflammatory processes such as rheumatoid nodules producing false-positive FDG results. An 85-year-old man presented to our PET Centre for FDG positron emission tomography (PET) evaluation of a left upper lobe pulmonary lesion found on computed tomography (CT). The pulmonary lesion was mildly FDG-avid, raising the possibility of malignancy. A left upper lobe segmentectomy was performed and the nodule was found to be benign pulmonary nodular amyloid. This case emphasizes the limitations of specificity of FDG PET in characterizing pulmonary nodules and the importance of confirming suspected malignancy with histology before potentially curative treatment is undertaken.