Staphylococcus infection-associated glomerulonephritis mimicking IgA nephropathy.

The association of methicillin-resistant Staphylococcus aureus (MRSA) infection with glomerulonephritis (GN) has been well documented in Japan but not in North America. Recently, eight renal biopsies with IgA-predominant or -codominant GN from eight patients with underlying staphylococcal infection, but without endocarditis, were observed at a single institution in a 12-mo period. Renal biopsies were worked up by routinely used methodologies. Eight cases of primary IgA nephropathy were used as controls. Five patients had MRSA infection, one had methicillin-resistant S. epidermidis (MRSE) infection, and two had methicillin-sensitive S. aureus infection. Four patients became infected after surgery; two patients were diabetic and had infected leg ulcers. All patients developed acute renal failure, with active urine sediment and severe proteinuria. Most renal biopsies showed only mild glomerular hypercellularity. Two biopsies had prominent mesangial and intracapillary hypercellularity; one of them (the MRSE-associated case) had large glomerular hyalin thrombi. This patient also had a positive cryoglobulin test. Rare glomerular hyalin thrombi were noted in two other cases. Immunofluorescence showed IgA pre- or codominance in all biopsies. Electron microscopy revealed mesangial deposits in all cases. Five biopsies had rare glomerular capillary deposits as well. In the MRSE-associated GN, large subendothelial electron-dense deposits were present. These cases demonstrate that staphylococcal (especially MRSA) infection-associated GN occurs in the US as well, and a rising incidence is possible. It is important to differentiate a Staphylococcus infection-associated GN from primary IgA nephropathy to avoid erroneous treatment with immunosuppressive medications.