A Case of Myeloperoxidase Antineutrophil Cytoplasmic Antibody (MPO-ANCA)-Positive Membranoproliferative Glomerulonephritis With Latent Tuberculosis Infection

Membranous proliferative glomerulonephritis (MPGN), also known as mesangiocapillary glomerulonephritis, is a relatively rare glomerulonephritis with characteristic pathology. We report the case of a 77-year-old man who presented with mild proteinuria and hematuria. Laboratory tests revealed increases in myeloperoxidase (MPO)-antineutrophil cytoplasmic antibody (ANCA) titers (15.9 U/mL), negative reaction for antinuclear antibodies, hematuria, and proteinuria (3.33 g/day). The patient was a carrier of Mycobacterium tuberculosis with positive results in the enzyme-linked immunosorbent assay, but negative in the sputum examination. Renal biopsy revealed double contours of the glomerular basement membrane, granular deposits of immunoglobulin (Ig) G and C3 along the capillary wall, mesangial areas, and high electron density deposits in the endothelium and subepithelium, leading to the diagnosis of MPGN type 3. The patient achieved remission only with sodium-glucose cotransporter-2 (SGLT2) inhibitor without immunosuppressive drugs. Secondary MPGN can be associated with various diseases, but the relationship between elevated MPO-ANCA levels and latent tuberculosis infection remains unclear. Consequently, there have been few reports of MPO-ANCA-positive MPGN in the context of latent tuberculosis infection. Our case report suggests a possible pattern of MPO-ANCA-positive MPGN linked to latent tuberculosis.