Diagnosis of IgG4-Related Disease: No Longer an IS(H)-Sue?
Julie Y Tse, Nicolo Riggi, David T Ting, John H Stone, Miguel Rivera, Vikram Deshpande. Massachusetts General Hospital, Boston, MA
Background: IgG4-related disease (IgG4-RD) is a tumefactive fibroinflammatory disease with elevated levels of serum and tissue IgG4. A histologic diagnosis of IgG4-RD requires the presence of elevated numbers of IgG4-positive plasma cells and an elevated IgG4 to IgG ratio (>40%). However, immunohistochemical (IHC) stains for IgG4 and IgG are frequently associated with high background signal, an artifact that makes quantitative analysis difficult. RNA in-situ hybridization (ISH) offers an attractive alternative assay to quantitate expression of genes that are challenging for IHC, however, this method has historically been difficult to perform in a reliable fashion. Recently developed branched DNA (bDNA) technology has overcome this limitation of RNA ISH and has been successfully applied to formalin-fixed, paraffin-embedded tissue, providing a novel clinical diagnostic.
Design: Modified bDNA ISH probes were developed for IgG4 and IgG with Affymetrix QuantiGene ViewRNA technology. The probe for IgG4 was based on a sequence unique to this isotype, while the probe for IgG was based on a sequence common to all isotypes as identified in the NCBI nucleotide database. We evaluated 14 cases of IgG4-RD and 30 control cases that mimicked IgG4-RD either clinically or histopathologically, including biopsies from all sites known to be involved by the disease. IHC analysis for IgG4 and IgG was also performed. Three high power fields (HPF) were counted on the ISH and IHC stains and the results expressed per HPF.
Results: ISH stains for IgG4 and IgG showed strong signal in plasma cells without background. This high quality signal was also seen in the 14 cases in which IHC stains for IgG4 and/or IgG showed strong background staining that precluded quantitative evaluation. The mean number of IgG4-positive cells per HPF by ISH was 23.42, and 27.24 by IHC (p-value = 0.17). The mean number of IgG-positive cells per HPF by ISH was 104.6, and 80.6 by IHC (p-value = 0.006). The mean IgG4 to IgG ratio by ISH was 0.17, and 0.32 by IHC (p-value = 0.001). The IgG4 counts and IgG4 to IgG ratio quantified by ISH provided a more robust distinction of IgG4-RD from cases mimicking IgG4-RD. Also significantly, IgG4-positive lymphocytes were identified in 5 of 14 cases of IgG4-RD, but in only 1 of the 30 control cases.
Conclusions: ISH stains for IgG4 and IgG provide a high signal to noise ratio, increasing the accuracy of quantitative evaluation. The IgG counts performed by ISH tend to be lower than by IHC. Our data also suggests the presence of IgG4-positive lymphocytes in tissue may represent an additional marker for distinguishing IgG4-RD from its mimics.
Monday, March 4, 2013 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 119, Monday Morning