The incidence of IgG4-positive plasma cells staining TIN in patients with biopsy-proven tubulointerstitial nephritis.

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.