A case of immunotactoid glomerulopathy with false-negative IgG staining

Immunotactoid glomerulopathy (ITG) is a rare glomerulonephritis characterized by microtubular deposits. Immunofluorescence findings are necessary to differentiate ITG from other proliferative glomerular diseases. The characteristic tubular structure on electron microscopy is essential for a definitive diagnosis, and the diameter of the structure has been traditionally used for differentiating between ITG and other types of glomerulonephritis with organized deposits. In recent years, the disease concept of monoclonal gammopathy of renal significance, which is associated with M protein produced by plasma cell tumors, has been proposed.

This was a peculiar case of ITG with underlying monoclonal gammopathy in which IgG showed a false-negative result with immunofluorescence using frozen sections. Additional examinations using a different clone of the anti-IgG antibody revealed typical IgG staining. C4d was strongly positive, consistent with immune complex type glomerulonephritis.

This case highlights unusual features of ITG, and provides a practical hint to avoid a diagnostic pitfall.