Discussion on the utility of FDG-PET for IgG4-associated systemic disease

Objectives The current concept of autoimmune pancreatitis (AIP), including various associated extrapancreatic lesions, suggests that it is a systemic disease histopathologically showing fibrosclerosis with immunoglobulin G4 (IgG4)-positive plasma cell infiltration. On the other hand, a new clinical entity “IgG4-positive multiorgan lymphoproliferative syndrome (IgG4+MOLPS)” characterized by extensive IgG4-positive plasma cell infiltration in various organs, e.g. IgG4-related Mikulicz disease, is also advocated. The aim of this study was to verify the similarity and difference between these two concepts using FDG-PET, and to evaluate the clinical utility of FDG-PET for these diseases.

Methods We studied 13 patients that satisfied the Asian diagnostic criteria of AIP and 8 patients that satisfied the proposed diagnostic criteria of IgG4+MOLPS (Ann Rheum Dis. 2009; 68:1310) who underwent FDG-PET (or PET/CT). Those who met the both criteria were classified into the AIP group. We compared the prevalence of involved organs between the two groups. Also, the detection rate of lesions by FDG-PET was evaluated.

Results In our study, bile duct and gallbladder lesions were observed only in AIP patients (31% and 23%, respectively). On the other hand, submandibular glands and ocular adnexa were affected significantly more often in IgG4+MOLPS patients than in AIP patients (75% VS 23%, 63% VS 8%, respectively). In the other affected organs, the difference was not statistically significant. FDG-PET detected the majority of the lesions (86% - 100%), except in the bile duct (0%), kidney (25%), or perirenal soft tissue (33%).

Conclusions FDG-PET, as whole-body imaging, provides objective information and is excellent for detecting the activated lesions of IgG4-related diseases. Prospective FDG-PET/CT studies would warrant to elucidate chaos about IgG4-associaed systemic disease