Prognostic associations of clinical and histopathological features in renal amyloidosis

Prognostic value of histopathological scoring and grading in patients with renal AA amyloidosis

OBJECTIVE

The amount and distribution pattern of amyloid deposits may contribute to renal function and outcome, given the great diversity of renal involvement in amyloidosis. The aim of this study was to analyze the impact of histological characteristics of patients with biopsy-proven renal AA amyloidosis (AAA) on renal outcome.

METHODS

Renal biopsies of 37 patients with AAA were re-evaluated. The distribution pattern of glomerular amyloid (GA) deposits was classified, the extent of amyloid deposits in glomeruli, vessel, and interstitium and other histopathologic lesions were scored, and renal amyloid prognostic score (RAPS) was determined by summing all scores. Their potential prognostic relevance on renal outcome was investigated.

RESULTS

GA and vascular amyloid (VA) deposits were noted in all cases, interstitial amyloid (IA) was detected in 70.2%. GA deposits were predominantly seen in diffuse mesengiocapillary fashions (class IV) (51.4%). GA class, the extent of GA, VA, IA deposit, and RAPS, as well as interstitial fibrosis (IF) and interstitial inflammation were correlated to renal function at diagnosis. During the median follow-up of 52 months, 13 patients developed doubling of serum creatinine or end stage renal disease and they had a higher degree of GA and VA load (p = 0.03 and p = 0.042, respectively) as compared to the remaining patients. VA load, but not GA and RAPS grade, was associated with poor renal outcome (HR 3.016, 95% CI 1.45-6.25, p = 0.003).

CONCLUSIONS

Baseline renal function is closely linked to the extent of AA amyloid deposit in renal parenchyma but only VA load was a predictor of renal outcome in AAA patients.

Renal Amyloidosis: A Clinicopathological Study From a Tertiary Care Hospital in Pakistan

Introduction

Systemic amyloidosis can affect any organ in the body, but the kidney is the most commonly involved site. It is characterized by the extracellular deposition of insoluble fibrillar proteins. Amyloid deposits can be identified histologically by Congo red stain, which gives apple-green birefringence under polarized light. Typing of renal amyloidosis is done by direct immunofluorescence on frozen tissue. The most common types of amyloidosis seen in renal tissue are amyloid light chain (AL) primary amyloidosis and amyloid A (AA) secondary amyloidosis. Although primary amyloidosis is considered the most common type in western countries, however, in the subcontinent region, secondary amyloidosis is more common.

The spectrum of signs and symptoms in renal amyloidosis is variable including isolated proteinuria, nephrotic syndrome, hypertension, hypotension, and renal insufficiency. The present study aims to evaluate the incidence and aetiology of various types of renal amyloidosis, determine their distribution within the kidney, and study various clinicopathological features.

Objective

The present study aims to evaluate the aetiology and clinicopathological profile of renal amyloidosis, determine its various types, and their distribution within the kidney.

Materials and methods

This retrospective cross-sectional study was conducted from 1st January 2013 to 31st December 2020 at the Department of Histopathology, Shifa International Hospital (SIH), Islamabad. All renal biopsies diagnosed as renal amyloidosis were included in the study. Data were analysed using SPSS version 23 (IBM Corp., Armonk, NY). Frequency and percentages were calculated for qualitative variables, and mean and standard deviation were calculated for quantitative variables.

Results

A total of 131 cases were diagnosed with renal amyloidosis during the study period of eight years (from 1st January 2013 to 31st December 2020) at SIH. The age range varied from 17 to 82 years. The mean age of the patients was 45 ± 16.33 years. Out of 131 patients, 82 (62.6%) were males and 49 (37.4%) were females. Amongst them, 72 (54%) cases were diagnosed with secondary AA amyloidosis and 16 (12%) cases were diagnosed with primary AL amyloidosis. The rest of the cases 43 (34%) were of indeterminate type. The associated conditions in secondary amyloidosis were tuberculosis in 41 (57%), rheumatoid arthritis in 16 (22%), ankylosing spondylitis in five (7%), lymphoma in three (4%), diabetes in two (3%), and chronic osteomyelitis, chronic heart disease, hepatitis, and vasculitis in one case each (1.7%). Out of 16 cases reported with AL amyloidosis, 10 cases (62.5%) had a history of multiple myeloma. The most common clinical presentation was nephrotic syndrome followed by subnephrotic proteinuria, renal failure, and hypertension.

Conclusion

The findings of the present study show underlying etiological factors and clinicopathological characteristics of renal amyloidosis. AA amyloidosis is the most common type of renal amyloidosis in our study and tuberculosis is the most common aetiological factor. AL amyloidosis is less frequent in our population.

A histopathological scoring and grading system to predict outcome for patients with AA amyloidosis

PURPOSE

Renal involvement is associated with significant morbidity and mortality in AA amyloidosis. Extend of amyloid deposition in kidney biopsies may be predictive for clinical manifestations and outcomes. The aim of our study is to assess clinical features of patients with biopsy-proven renal AA amyloidosis and to evaluate the relationship between histopathological scoring and grading of renal amyloid deposition with clinical findings and outcomes.

METHODS

The study included 86 patients who were diagnosed with renal AA amyloidosis. The demographic and clinical features at the time of biopsy and follow-up data were retrospectively collected. Amyloid deposition in glomeruli, interstitium, vessels and tubulointerstitial findings were scored and renal amyloid prognostic score (RAPS) was assigned by adding all scores. RAPS was further divided into three grades (RAPS grade I, II, III).

RESULTS

Median age was 50 (36-59) years. Familial Mediterranean fever was the leading cause. RAPS grade and interstitial inflammatory infiltration were associated with baseline eGFR and glomerular amyloid deposition was associated with proteinuria. During the follow-up period (median 50 months), 39 patients developed ESRD. Extensive (involving > 50%) glomerular amyloid deposition, baseline eGFR and proteinuria were independent risk factors for progression to end stage renal disease. Death censored renal survival was significantly lower among patients with RAPS grade III compared to those with RAPS grade I and II. Patient survival rate was not different according to RAPS grade.

CONCLUSIONS

Degree of renal amyloid accumulation is associated with renal function and outcome. The scoring and grading system may be predictive in clinical outcome and contribute to understanding of disease mechanism.

Renal amyloidosis: validation of a proposed histological scoring system in an independent cohort

Background

In systemic amyloidosis, the kidney is frequently affected and renal involvement has a major impact on survival. Renal involvement is clinically characterized by decreased estimated glomerular filtration rate (eGFR) and proteinuria. The two most common renal amyloidosis types are light chain-related amyloidosis (AL) and serum amyloid A (AA) amyloidosis. Standardized histopathological scoring of amyloid deposits is crucial to assess disease progression. Therefore, we aimed to validate the proposed scoring system from Rubinstein et al. (Novel pathologic scoring tools predict end-stage kidney disease in light chain (AL) amyloidosis. Amyloid 2017; 24: 205–211) in an independent patient cohort.

Methods

We attempt to reproduce the scoring system, consisting of an amyloid score (AS) and a composite scarring injury score (CSIS), in a multicentre AL and AA case series. Additionally, we analysed all renal amyloidosis kidney biopsies performed in the Netherlands between 1993 and 2012.

Results

Similar to the original study, AS and CSIS correlated to eGFR (r = −0.45, P = 0.0061 and r = −0.60, P < 0.0001, respectively) but not to proteinuria at diagnosis. Furthermore, AS, but not CSIS, was associated with renal outcome. The scoring system was not reproducible in AA patients. The median incidence rate for renal amyloidosis in the Netherlands was 2.3 per million population per year, and increased during the study period.

Conclusions

In our AL case series and the original study, AS and CSIS were correlated to eGFR but not to proteinuria, and AS correlated with renal outcome. Overall, we regard this scoring system as competent for standardized histopathological assessment of amyloid deposits burden and thereby disease advancement in renal biopsies.