Subepithelial argyrophilic spicular structures in renal amyloidosis--an aid in diagnosis. Pathogenic considerations

Significant association between renal function and area of amyloid deposition in kidney biopsy specimens in both AA amyloidosis associated with rheumatoid arthritis and AL amyloidosis

The kidney is a major target organ for systemic amyloidosis, which results in proteinuria and an elevated serum creatinine level. The clinical manifestations and precursor proteins of amyloid A (AA) and light-chain (AL) amyloidosis are different, and the renal damage due to amyloid deposition also seems to differ. The purpose of this study was to clarify haw the difference in clinical features between AA and AL amyloidosis are explained by the difference in the amount and distribution of amyloid deposition in the renal tissues. A total of 119 patients participated: 58 patients with an established diagnosis of AA amyloidosis (AA group) and 61 with AL amyloidosis (AL group). We retrospectively investigated the correlation between clinical data, pathological manifestations, and the area occupied by amyloid in renal biopsy specimens. In most of the renal specimens the percentage area occupied by amyloid was less than 10%. For statistical analyses, the percentage area of amyloid deposition was transformed to a common logarithmic value (Log₁₀%amyloid). The results of sex-, age-, and Log₁₀%amyloid-adjusted analyses showed that systolic blood pressure (SBP) was higher in the AA group. In terms of renal function parameters, serum creatinine, creatinine clearance (Ccr) and estimated glomerular filtration rate (eGFR) indicated significant renal impairment in the AA group, whereas urinary protein indicated significant renal impairment in the AL group. Pathological examinations revealed amyloid was predominantly deposited at glomerular basement membrane (GBM) and easily transferred to the mesangial area in the AA group, and it was predominantly deposited at in the AL group. The degree of amyloid deposition in the glomerular capillary was significantly more severe in AL group. The frequency of amyloid deposits in extraglomerular mesangium was not significantly different between the two groups, but in AA group, the degree amyloid deposition was significantly more severe, and the deposition pattern in the glomerulus was nodular. Nodular deposition in extraglomerular mesangium leads to renal impairment in AA group. There are significant differences between AA and AL amyloidosis with regard to the renal function, especially in terms of Ccr, eGFR and urinary protein, even after Log10%amyloid was adjusted; showing that these inter-group differences in renal function would not be depend on the amount of renal amyloid deposits. These differences could be explained by the difference in distribution and morphological pattern of amyloid deposition in the renal tissue.

A practical approach to the diagnosis of renal disease by biopsy

The pathologist has an important role in the diagnosis and monitoring of renal disease. However, for optimal useful information to be derived from renal biopsy specimens, certain guidelines must be adhered to and these are enunciated here. The 3 avenues of observation of renal biopsies viz. light microscopy, immunofluorescence and electron microscopy, all have important roles to play and give differing data which informs the diagnosis for the renal biopsy report. The relative emphasis on each of these modalities of investigation will vary depending upon the situation in which the renal biopsy is performed. The methods used here have been shown to be effective in practice over a period of 20 yrs. Although there may be variations in methodology from centre to centre, the general background aims and principles remain the same. The emphasis in this paper has been on common practical aspects of renal biopsies. Much of the practical information concerning renal biopsies, which is brought together here, is otherwise scattered and not readily available. The aim of this article is to allow the reader to understand the rationale for the steps that are involved in renal biopsy diagnosis.

Renal amyloidosis. Correlations between morphology, chemical types of amyloid protein and clinical features

Sixty-one autopsy cases of renal amyloidosis were reviewed to assess the relationship of renal pathology to chemical types of amyloid and clinical features. Glomerular amyloid deposition was divided on the basis of morphological characteristics, into four types: a mesangial nodular type showing nodular mesangial deposits with sparse capillary wall involvement (25 cases), a mesangio-capillary type disclosing diffuse amyloid deposition in the mesangium and along both sides of the glomerular basement membrane (19 cases), a perimembranous type principally involving the subepithelial side of the basement membrane invariably characterized by exuberant spicular arrangement (6 cases), and a hilar type showing amyloid deposits almost exclusively in hilar arterioles (11 cases). Twenty-four of 25 cases of mesangial nodular type (96%) showed amyloid protein of AA type. However, mesangio-capillary and perimembranous types were associated with deposition of AL amyloid protein in 15 of 19 (79%) and all 6 cases, respectively. Nephrotic syndrome was more frequent in patients with AL amyloidosis; notably, all patients with perimembranous type had nephrotic syndrome irrespective of the extent of glomerular amyloid deposits. Chronic renal failure and renal death appeared more common in mesangial nodular type in which the extent of glomerular amyloidosis correlated with that of vascular amyloid deposits. The results obtained suggest that the chemical type of glomerular amyloid protein (AA vs AL) is associated with significant differences in the morphological, clinical and prognostic features of the renal involvement.

Cystitis cystica: an electron and immunofluorescence microscopic study

Cystitis cystica was studied with the aid of electron and immunofluorescence microscopy. By electron microscopy, the epithelium demonstrated morphologic features suggestive of an active metabolism. Secretory-type granules were seen in the cytoplasm just beneath the luminal membrane of surface columnar cells. Microvilli of the plasma membrane also were seen at the luminal surface. Rough endoplasmic reticulum and Golgi apparatuses were present. The cells were rich in mitochondria. By immunofluorescence microscopy, IgA, secretory piece and IgM were localized in the epithelial cells, especially at the luminal surfaces. IgG was occasionally found. These findings contrast markedly with the transitional cells and their relatively scanty content of secretory-type organelles. In addition, they may explain the large amounts of IgA in the urine of patients with cystitis cystica.

Acellular scanning electron microscopy of spicular renal amyloidosis

Two human renal biopsies containing glomerular amyloid deposits organized into spicular formations (spicular amyloid) were studied by scanning electron microscopy following removal of the cellular components (acellular SEM). Following SEM studies, portions of the same acellular tissue were embedded in paraffin and plastic for light microscopy and transmission electron microscopy, respectively. Spicular deposits by acellular SEM appear as tapering conical formations interconnected by a delicate branching network of fibrils, which imparts a higher degree of organization than previously appreciated by two-dimensional LM and TEM. Silver stains of paraffin- and plastic-embedded acellular tissue showed persistence of argyrophilia in spicular deposits, while acellular TEM showed that the spicules appeared comprised "purely" of amyloid fibrils without visible contaminating material. We conclude that the argyrophilia of spicular amyloid is an inherent feature of the parallel organization of fibrils rather than a result of incorporation of glomerular basement membrane or cell components and that spicular amyloid deposits have a higher degree of organization than is apparent by two-dimensional studies.

Renal cell carcinoma and systemic amyloidosis: demonstration of AA protein and review of the literature

A case of renal cell carcinoma associated with systemic amyloidosis in a patient with nephrotic syndrome is presented. Amyloid deposits were present in the resected tumor, ipsilateral kidney, and spleen. Potassium permanganate treatment of histologic sections as well as immunoperoxidase staining identified AA protein within the amyloid. Surgical removal of the tumor caused marked remission of the patient's proteinuria. Thirty-nine previously reported cases of renal cell carcinoma with amyloidosis are reviewed. Most tumors have clear cell histologic features, and the amyloid distribution follows the "secondary" pattern. A possible mechanism of amyloid production in renal cell carcinoma is presented in which the tumor directly or indirectly participates in the modification of SAA protein into a precipitable form.