Subepithelial deposits are observed in rare adult
IgA nephropathy (IgAN) cases and are a key diagnostic finding in
IgA-dominant
infection-related
glomerulonephritis (IgA-IRGN). Sometimes, it is difficult to distinguish
IgA-IRGN from IgAN without a precise clinical history. We hypothesized that some
IgA-IRGN cases might be diagnosed as IgAN with subepithelial deposits (IgAN-SD) and aimed to clarify the significance of subepithelial deposits in patients diagnosed with IgAN. We examined 464 patients diagnosed with IgAN at Nagasaki University Hospital and affiliated hospitals between 1996 and 2013. The differences in clinicopathological findings between IgAN-SD and IgAN with no subepithelial deposits (IgAN-NSD) were investigated. In addition to clinical data and typical IgAN pathological features, we analyzed
complement levels,
immunoglobulin localization, light chain staining patterns, and intramembranous deposits. There were 214 men and 250 women with a mean age of 38.8 ± 18.3 years. Subepithelial deposition was observed in 51 patients (11%). Compared to patients with IgAN-NSD, those with IgAN-SD had significantly lower mean
serum protein (6.4 g/dL vs. 6.7 g/dL; p = 0.02),
albumin (3.7 g/dL vs. 3.9 g/dL; p = 0.02), and
complement (C3) (94 mg/dL vs. 103 mg/dL; p = 0.02) levels. Diffuse mesangial hypercellularity (M) (65% vs. 45%; p<0.01), endocapillary hypercellularity: (E) (43% vs. 28%; p = 0.03), and
IgA staining in the glomerular capillary wall (22% vs. 8%; p<0.01) were more common in patients with IgAN-SD. The incidence of light chain lambda predominance was lower in patients with IgAN-SD (47% vs. 63%; p = 0.03). Hump-shaped subepithelial deposits and intramembranous deposits were observed in nine and 17 patients with IgAN-SD, respectively. Patients with IgAN-SD tended to have the characteristics of
IgA-IRGN rather than IgAN-NSD. Since the therapeutic strategies for
IgA-IRGN differ from those for IgAN, we should review the clinical history and pay careful attention to the
clinical course in cases with atypical findings, such as subepithelial deposits.