Alok Kumar Gupta1, Serge Jothy2, Peter Somerville3, Jeffrey S Zaltzman1. 1. Department of Nephrology, St. Michael's Hospital, University of Toronto, Toronto, Canada. 2. Department of Laboratory Medicine and Pathobiology, St. Michael's Hospital, University of TorontoCanada. 3. Grand River Hospital, Kitchener, ON, Canada E-mail: Alok_bgupta@yahoo.co.in.
Dear Sir,We thank Ben Sprangers and Kathleen Claes for their valuable comment on our case report ‘Hypocomplementaemic immune complex tubulointerstitial nephritis’ [1]. We agree that immunoglobulin G4 (IgG4)-related systemic disease is a potential differential diagnosis in our case. Predominant male disease, autoimmune immune complex nature, low complements, positive antinuclear antibody (ANA), tubulointerstitial involvement and good response to steroids remain common features [2,3]. Unfortunately, immunoglobulin levels, in particular IgG4, and specific tissue staining for IgG4 were not measured and done in our case. It is the same scenario for previously reported cases of hypocomplementaemic idiopathic immune complex tubulointerstitial nephritis (TBIN) that we mentioned in our case report [1,2]. In the absence of this evidence, presence or absence of IgG4 disease in reference to our case remains a speculation.On reviewing the literature of IgG4 disease, we noted some important differences. Most of the cases of IgG4 disease have concurrent or subsequent systemic involvement [3]. On the contrary, there was no evidence of systemic or extrarenal disease in our case even after a follow-up of 18 months [1]. In the largest reported series of cases of hypocomplementaemic idiopathic immune complex TBIN by Kambham et al., there were two cases of sclerosing cholangitis which could be potentially indicative of IgG4 disease [2]. However, autoimmune pancreatitis, which is one of the most commonly reported features of IgG4 disease, was conspicuous by its absence in all the reported cases of idiopathic TBIN [1-3]. Also, no significant glomerular disease has been reported in cases of idiopathic TBIN, while membranous and membranoproliferative glomerulonephritis have been reported with IgG4 disease [1,2,4,5]. We could not find any reported case of IgG4 disease with tubulointerstitial nephritis and no extrarenal involvement. There are cases described without pancreatitis, but even they have some extrarenal involvement in terms of sialadenitis and lymphadenopathy [6].In conclusion, it is difficult to say whether our case has IgG4 disease as aetiology due to lack of IgG4 levels and tissue staining and in the light of available literature.Conflict of interest statement. None declared.