Clinicopathological Findings, Electron Microscopy, and Classification of Renal Amyloidosis: A 16-Years Survey

The electron microscopy (EM) study is valuable in the diagnosis of renal amyloidosis, particularly in the early stages. There are scanty EM studies and clinical picture of renal amyloidosis in Iran. In addition, some pathological classifications were done for renal amyloidosis. But comparing two classifications based on glomerular involvement and based on the number of involved main renal components (glomerulus, tubule, vessels, and interstitium) did not perform. The purpose of this study is an investigation of EM study, pathological classifications, and clinical features of renal amyloidosis. Methods:In this cross-sectional study, we investigated 27 out of 2865 kidney biopsies with a diagnosis of renal amyloidosis sent to the EM unit affiliated to Shiraz University of Medical Sciences from 2001 to 2016. EM and six stainings for light microscopy (LM) study were done. The value of the EM study was categorized as necessary, supportive, and non-necessary. Two modified pathological classifications were performed. The first was based on the number of involved main renal components (glomerular, peritubular, perivascular, and interstitial amyloid depositions), and the second, was based on the percentage of only glomerular involvement. Finally, the association between these two classifications and clinical characteristics was assessed using chi-square, Fisher’s exact test, and multiple logistic regression.Results:0.94% of all kidney biopsies were renal amyloidosis, and 59.3% of patients were male. Clinical diagnosis of 51.9% of the patients was a nephrotic syndrome. Proteinuria and edema were the most prevalent clinical manifestations. In one-third of patients, Congo Red staining was negative. EM study was necessary or supportive for the diagnosis of 48.2% of patients. In the classification based on glomerular classes, mean blood pressure(P=0.003), having a history of hypertension(P=0.02), creatinine > 1.5 (P=0.03), and severe tubular atrophy(P=0.03) were significantly higher in class B (with advanced (> 76%) amyloid depositions) than class A (less than 76% depositions). Conclusions:The EM study has an important role in the diagnosis of renal amyloidosis. Hence, in patients with clinically suspicious to renal amyloidosis, in addition to LM study with Congo red staining, EM study could help to prevent misdiagnosis. Also, among different pathological features of renal amyloidosis, the extent of glomerulus involvement in comparison with the number of involved main renal components had more correlation with clinical features and a better predictor of the clinical situation.

کلیدواژه ها:

Amyloidosis ، Microscopy ، Electrons ، Transmission ، Proteinuria ، Nephrotic Syndrome ، Kidney