The significance of atypical morphology in the changes of spectrum of postinfectious glomerulonephritis.

BACKGROUND: The characteristics of post infectious glomerulonephritis (PIGN) now differ from what were described decades ago. After encountering several patients of PIGN with atypical morphology, we conducted this retrospective study to determine the significance in the changes of clinicopathological spectrum of the disease.

METHODS: Between July 2000 and February 2009, 21 cases of PIGN were identified at a medical center in Taiwan. The patients' records were reviewed with respect to clinical presentation, microbiology, serology, morphology of renal biopsy, and clinical course.

RESULTS: The mean age was 60.4 years. All patients developed acute renal failure and the majority (66.7%) required dialysis support. Hypocomplementemia was present in 61.9% of patients. The most frequently identified infectious agent was Staphylococcus (57.1%). Histological characteristics showed two distinct patterns of PIGN. One was diffuse endocapillary proliferation typical of PIGN (61.9%) and the other was atypical pattern of focal mesangial proliferation (38.1%). In comparison, glomerular neutrophil infiltration was more commonly present in typical pattern (p = 0.018). Glomerular IgA dominant or co-dominant deposition was more frequently seen in atypical pattern (p = 0.032). However, there were no statistically significant differences in the clinical presentation and outcome between the two groups. Our data also showed that the percentage of patients with atypical morphology PIGN significantly increased over time.

CONCLUSIONS: Atypical pattern of focal mesangial proliferative glomerulonephritis may represent a resolution stage of PIGN. The nature of subclinical infection with a more protracted course may contribute to the increasing recognition of this resolving PIGN at the time of renal biopsy. Another possible explanation is that the atypical morphology may be a peculiar pattern of poststaphylococcal glomerulonephritis which was increasingly identified in PIGN over the past 10 years.