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Unusual positron emission tomography findings in pulmonary amyloidosis: a case report
© Yadav et al; licensee BioMed Central Ltd. 2006
Received: 26 June 2006
Accepted: 05 October 2006
Published: 05 October 2006
Positron emission tomography (PET) has come to play an increasingly important role in the evaluation of pulmonary lesions, which are suspicious of malignancy. As is true for other techniques, PET gives false positive and negative results. We report a case of pulmonary amyloidosis with multiple pulmonary nodules showing different uptake of 18 F-fluorodeoxyglucose (FDG) on PET. There are limitations of specificity of FDG-PET in characterising pulmonary nodules and it is important to confirm a suspected malignancy with histology before potentially curative treatment is undertaken.
PET imaging is a technology that is used to identify focal areas of increased cellular metabolism. FDG is an excellent tracer for detecting malignant disease because of high glucose metabolism observed in cancer cells. With this technique whole body image can be created to accurately identify malignant primary neoplasm and metastatic disease.
For pulmonary lesions FDG-PET has been used to differentiate malignant from benign lesions and to stage and follow patients with lung cancer. PET has demonstrated sensitivity and specificity rates of 80–90% compared to 50–60% for CT . Low-grade malignant lesions such as carcinoids and localised broncho-alveolar carcinomas have shown low to intermediate glucose metabolism and negative PET images . On other hand, there have been reports of false positive PET in metabolically active benign lesions like tuberculous granulomas, coccidiomycosis and aspergillosis [3, 5]. There have been anecdotal case reports of false positive PET in pulmonary amyloidosis [5, 6].
Amyloidosis is a disorder in which insoluble protein fibres become deposited in tissues and organs. The exact mechanism that causes amyloidosis is unknown. However, primary amyloidosis appears to be related to abnormal production of amino globulins by plasma cells whereas secondary amyloidosis is associated with the presence of chronic inflammation of infectious disease. A variety of inflammatory and infectious disorders can result in increased FDG activity. Gallium 67, an inflammatory seeking agent, has been reported to have shown intense uptake in amyloid goitre as a result of inflammatory action. It is conceivable that inflammatory action caused by amyloid lesion result in increased FDG uptake. What makes our case interesting is the fact that in the same patient different amyloid nodules had different uptake of FDG on PET.
This case emphasises the limitations of specificity of FDG-PET in characterising pulmonary nodules and the importance of confirming suspected malignancy with histology before potentially curative treatment is undertaken. Further studies for mechanism of such false positive results on PET scan are warranted.
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