Aim IgG4 disease is rare. However, IgG4 tubulointerstitial nephritis (TIN) is the most common renal manifestation. IgG4 disease is usually associated with elevated serum IgG4 levels and other organ involvement, low-density renal lesions on enhanced CT imaging and immune activation. The incidence of IgG4-TIN may be underestimated, as staining for IgG4 is not routine. This study sought to describe the prevalence of previously undiagnosed IgG4-TIN. Due to the complexity of the diagnosis, we only attempt to look at IgG4-positive plasma cell TIN as a potential indication for IgG4 renal disease.
Methods A retrospective review of native renal biopsies performed between 2002 and 2012 with a primary diagnosis of TIN was selected. Samples for which interstitial nephritis was secondary to a glomerular disease were excluded. The tissues were stained for IgG4 and scored by two blinded observers. Demographic and follow-up details were collected. This study was approved by the local ethics committee.
Results 82 cases of interstitial nephritis from a total of 1238 renal biopsies (2002–2012) were available after staining for further assessment. 12 samples demonstrated staining consistent with the criteria for IgG4-positive plasma cell TIN, of which 3 had mildly positive staining, 7 moderately positive staining and 2 had markedly positive staining. There were no statistically significant differences in the baseline characteristics between the positive and negative staining groups.
Conclusions A number of cases of IgG4-positive plasma cell TIN were observed histologically that had been previously diagnosed as non-specific chronic TIN. IgG4-positive plasma cell TIN made up 1% of all renal biopsies performed over 10 years and 13% of all biopsies demonstrating TIN not related to glomerular disease. IgG4 staining should be considered routinely in biopsies demonstrating primary TIN.
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Handling editor Cheok Soon Lee
Contributors My coauthors have all contributed to this manuscript and approved this submission. KM was the primary investigator who was responsible for designing the study, reviewing the literature and histological slides, and drafting the manuscript. XJW was responsible for retrieving paraffin blocks and immune peroxidase staining of all histology slides. JM was responsible for generating the biopsy database. KH was responsible for the literature review and drafting the manuscript. MS was responsible for supervising the project and drafting the manuscript. JY was responsible for supervising and reviewing all the histopathology slides and assisted with any histopathological related questions. AM was the main supervisor of this project who also designed the study, reviewed the literature, reviewed histopathology slides and finalised the manuscript.
Funding This work was supported and funded by the Department of Nephrology, South West Sydney Area Health Service.
Competing interests None declared.
Ethics approval Sydney South West Local Health District Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.