Utility of 18F-FDG PET(/CT) in patients with systemic and localized amyloidosis

Amyloidosis is a group of diseases characterized by deposition of fibrils and this deposition may be localized or systemic. The presence of giant cells is typical of localized AL amyloidosis in contrast to systemic amyloidosis. Because of this presence of giant cells we hypothesize that (18)F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) may show uptake in localized amyloidosis but not in systemic amyloidosis. The aim of the study was to evaluate the utility of (18)F-FDG PET/CT in distinguishing systemic amyloidosis from localized amyloidosis.

A retrospective search in the hospital computer system showed 21 patients with histologically proven systemic or localized amyloidosis who recently had undergone (18)F-FDG PET/CT. Twenty patients also had undergone (123)I-serum amyloid P component (SAP) scintigraphy.

Of 11 patients with localized amyloidosis, 10 showed markedly increased FDG uptake at the amyloid site, whereas one showed slightly increased FDG uptake. (123)I-SAP scintigraphy (in ten patients) was positive in three patients at the amyloid site and negative for any other specific organ involvement in nine patients, with a weakly positive spleen in one other patient. In ten patients with systemic amyloidosis, increased FDG uptake was not found in any affected organ containing amyloid, whereas (123)I-SAP scintigraphy was positive for specific organ involvement in nine patients.

(18)F-FDG PET/CT may be supportive of the usual diagnostic tests in differentiating between systemic amyloidosis (no increased FDG uptake at the amyloid site) and localized amyloidosis (increased FDG uptake at the amyloid site). Apart from diagnosis, this finding has potential clinical application in therapy evaluation and follow-up.