Solitary pulmonary amyloidoma in systemic lupus erythematosus mimicking lung cancer on 18F-FDG PET-CT scan: case report and mini-review of the literature.

Solitary tumour-like localized amyloid deposits (tumoral amyloidosis or amyloidoma) are uncommon. Nodular pulmonary amyloidoma is a rare form of amyloidosis confined to the lung parenchyma without any other organ involvement, and is typically an incidental finding. It can mimic a bronchopulmonary carcinoma and may occur secondarily to an infectious, inflammatory or lymphoproliferative disease. The association of amyloidosis, especially pulmonary amyloidoma, with systemic lupus erythematosus (SLE) is extremely unique. We report an exceptional case of a 62-year-old female patient with long- standing SLE who presented with radiologically-verified solitary pulmonary nodule in the right lower lobe that was discovered during diagnostic evaluation of a protracted febrile illness with productive cough despite several courses of antibiotic treatment. F-18 fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) scan is an essential imaging tool for investigation of such uncertain nodules, often used as an alternative to invasive procedures, to identify potential malignant lesions. A PET-CT scan of our patient revealed moderate to marked FDG uptake with maximum standardized uptake value (SUV max) of 5.25 in the known nodule. As the hypermetabolic lesion was suspicious of an early primary malignancy, tumour resection and right lower lobectomy was performed. The resected nodule contained large deposits of dense, amorphous eosinophilic material, partly surrounded by multinucleated giant cells and partly by granulation tissue or fibroblastic stroma, that stained positively for Congo red and was green birefringent under polarized light. Immunohistochemical methods confirmed amyloidoma and excluded lymphoproliferative disease. There were no signs of systemic amyloidosis. FDG-avid amyloid lung nodules on PET imaging are infrequent. To our knowledge, this is the first documented case of SLE-associated solitary pulmonary amyloidoma mimicking early lung cancer on 18F-FDG PET-CT scan of the thorax.