Background/Purpose:  IgG4-Related Disease (IgG4-RD) is a multisystemic inflammatory disease characterized by fibrous swelling and IgG4+ plasma cells infiltration of affected organs.18-Fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) scan is emerging as a promising imaging technique for diagnosis and staging of IgG4-RD. We aim to correlate the intensity and distribution of FDG-PET uptake with clinical and immunological parameters in patients with active untreated IgG4-RD.

Methods:  Patients with active, untreated, biopsy proven IgG4-RD were included in the study. Disease activity was assessed through clinical (IgG4-RD Responder Index (RI)) and immunological (erythrocyte sedimentation rate (ESR), C reactive protein (CRP), serum IgG4, and circulating plasmablasts) parameters. Plasmablasts, a recently characterized disease biomarker, were identified as CD19+CD20-CD27+CD38bright cells on flow cytometry. FDG-PET/CT was performed in all patients at diagnosis. Quantitative assessment of FDG uptake was measured using the mean Standardized Uptake Value corrected for the Partial Volume Effect (PVC-SUV) and with total lesion glycolysis (TLG). Lymph nodes < 1 cm of diameter were excluded from the analysis because of the risk of PVC-SUV over/under-estimation. In patients with multiorgan involvement, the IgG4-RD lesion with the highest PVC-SUV was selected to correlate FGD uptake with clinical and serological parameters.

Results:  We studied 19 patients (12 males, 7 females) with a mean age of 61 years (range, 30-78 years). Eleven (58%) patients had multiorgan IgG4-RD, with a average number of organ affected of 2.2 (range, 1-6). Involved organs were: lymphnodes (8 patients), aorta (6 patients), pancreas (4 patients); lung, parotids and submandibolar glands (3 cases each), paranasal sinuses, palate, orbits, bones and lachrymal glands (2 cases each); meninges, thyroid, subcutaneous nodule and spleen (one case each). The median IgG4-RD RI was 6 (range 6-15; normal < 3). The median levels of ESR, CRP, serum IgG4 and plasmablasts at baseline were 30 mm/h (range 4-121 mm/h, normal <20 mm/h), 9,9 mg/L (range 0.0-48.0 mg/L; normal <6mg/L), 455 mg/dL (range 80-2100 mg/dL, normal <135 mg/dL), and 5365 cells/mL (range 130-40840 cells/mL, normal <650 cells/mL), respectively. The mean PCV-SUV was 10.36 (range, 2.78-39.34) and the mean TLG was 429.24 (range, 91.37-3479.65). Significant positive correlation was found between PVC-SUV and circulating plasmablasts levels (r=.46, p=.004). No statistically significant correlation was found between either PVC-SUV or TLG and CRP, ESR, serum IgG4 levels, IgG4-RD RI at baseline (p>.05), and not even between TLG and circulating plasmablasts (p>.05). 

Conclusion:  We first demonstrated a positive correlation between circulating plasmablasts and inflammatory activity of IgG4-RD lesions as assessed by PVC-SUV on FDG-PET. Inflammatory markers, serum IgG4 levels, and IgG4-RD RI do not appear to correlate with metabolic activity in IgG4-RD lesions. Our results further strengthen the utility of circulating plasmablasts as a biomarker of IgG4-RD activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inflammatory-activity-of-igg4-related-disease-lesions-assessed-by-quantitative-positron-emission-tomography-correlates-with-circulating-plasmablasts-levels/