Fibrillary Glomerulonephritis: Clinicopathologic Features and Atypical Cases from a Multi-Institutional Cohort

BACKGROUND AND OBJECTIVES

Fibrillary GN has been defined as an immune complex-mediated GN with amyloid-like fibrils larger than amyloid which are IgG positive and Congo red negative. With discovery of DNAJB9 as a highly sensitive and specific marker for fibrillary GN, the specificity of the morphologic criteria for establishing the diagnosis of fibrillary GN has come into question.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We sought to (1) determine anatomic characteristics that best define fibrillary GN and (2) identify clinical and pathologic features that predict outcomes.

RESULTS

We retrospectively reviewed kidney biopsies from patients diagnosed with fibrillary GN or suspected fibrillary GN between 1997 and 2017 (n=266, 65% female, median age 61). Approximately 11% of kidney biopsies had one or more unusual feature including monotypic deposits, Congo red positivity, or unusual fibril diameter. Fibrillary GN as a possible monoclonal gammopathy of renal significance represented <1% of cases. Immunostaining for DNAJB9 confirmed fibrillary GN in 100% of cases diagnosed as fibrillary GN and 79% of atypical cases diagnosed as possible fibrillary GN. At a median time of 24 months (interquartile range, 8-46 months) after biopsy (n=100), 53% of patients reached the combined primary outcome of ESKD or death, 18% had CKD, and 18% had partial remission. On multivariable analysis, male sex (adjusted hazard ratio [aHR], 3.82; 95% confidence interval [95% CI], 1.97 to 7.37) and eGFR were the most significant predictors of primary outcome (aHR of 8.02 if eGFR <30 ml/min per 1.73 m2 [95% CI, 1.85 to 34.75]; aHR of 6.44 if eGFR 30 to <45 ml/min per 1.73 m2 [95% CI, 1.38 to 29.99]). Immunosuppressive therapy with rituximab was significantly associated with stabilization of disease progression.

CONCLUSIONS

Detection of DNAJB9 is a useful diagnostic tool for diagnosing atypical forms of fibrillary GN. The outcomes for fibrillary GN are poor and progression to ESKD is influenced predominantly by the degree of kidney insufficiency at the time of diagnosis and male sex. Rituximab may help preserve kidney function for select patients with fibrillary GN.

PODCAST

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Location of glomerular immune deposits, not codeposition of immunoglobulin G, influences definitive renal outcomes in immunoglobulin A nephropathy

Background

It has been suggested that the prognosis of immunoglobulin (IgA) nephropathy (IgAN) is adversely affected if there is codeposition of IgG in the glomeruli or if immune deposits are present in the glomerular capillary walls. We sought to understand how these variables affect clinical outcome.

Methods

A total of 80 IgAN biopsies were retrospectively divided into groups: (i) IgA without IgG deposition versus IgA + IgG and (ii) immune deposits restricted to the mesangium versus mesangium and peripheral capillary walls (PCWs). The association of these groups with the composite primary outcome of renal replacement therapy, renal transplant, death or doubling of serum creatinine (SCr) concentration was determined. The change in estimated glomerular filtration rate (eGFR) was also assessed. Covariates examined were age, sex, race, SCr and proteinuria level at biopsy and at follow-up, duration of follow-up, treatment, Oxford score and presence of crescents.

Results

IgG codeposition showed a trend toward endocapillary hypercellularity (P = 0.082); there were no other baseline differences between the IgA (n = 55) and IgA + IgG (n = 25) groups. At a median follow-up time of 29 months, the combined primary outcome was reached in 24 patients, 16 with IgA and 8 with IgA + IgG (P = 0.82). Patients with immune deposits in the PCWs (n = 21) presented with higher baseline proteinuria than those with deposits limited to the mesangium (n = 59; P = 0.025), were more likely to have crescents/segmental glomerular necrosis on biopsy (P = 0.047) and were more likely to reach the combined primary outcome (P = 0.026). Biopsies with crescents/segmental glomerular necrosis were associated with endocapillary hypercellularity (P < 0.001).

Conclusions

In this multicenter IgAN cohort, IgG co-deposition and the location of glomerular immune deposits in the PCWs were both associated with greater histologic activity on renal biopsy, but only the location of glomerular immune deposits in the PCWs was associated with a significantly increased risk for end-stage renal disease, transplant, death and/or doubling of SCr.

Low-dose agalsidase beta treatment in male pediatric patients with Fabry disease: A 5-year randomized controlled trial

BACKGROUND

Fabry disease is a rare, X-linked, lifelong progressive lysosomal storage disorder. Severely deficient α-galactosidase A activity in males is associated with the classic phenotype with early-onset, multisystem manifestations evolving to vital organ complications during adulthood. We assessed the ability of 2 low-dose agalsidase beta regimens to lower skin, plasma, and urine globotriaosylceramide (GL-3) levels, and influence clinical manifestations in male pediatric Fabry patients.

METHODS

In this multicenter, open-label, parallel-group, phase 3b study, male patients aged 5-18 years were randomized to receive agalsidase beta at 0.5 mg/kg 2-weekly (n = 16) or 1.0 mg/kg 4-weekly (n = 15) for 5 years. All had plasma/urine GL-3 accumulation but no clinically evident organ involvement. The primary outcome was GL-3 accumulation in superficial skin capillary endothelium (SSCE).

RESULTS

The mean age was 11.6 (range: 5-18) years and all but one of the 31 patients had classic GLA mutations. In the overall cohort, shifts from non-0 to 0-scores for SSCE GL-3 were significant at years 1, 3, and 5, but results were variable. Plasma GL-3 normalized and urine GL-3 reduced substantially. Higher anti-agalsidase beta antibody titers were associated with less robust SSCE GL-3 clearance and higher urine GL-3 levels. Renal function remained stable and normal. Most Fabry signs and symptoms tended to stabilize; abdominal pain was significantly reduced (-26.3%; P = .0215). No new clinical major organ complications were observed. GL-3 accumulation and cellular and vascular injury were present in baseline kidney biopsies (n = 7). Treatment effects on podocyte GL-3 content and foot process width were highly variable. Fabry arteriopathy overall increased in severity. Two patients withdrew and 2 had their agalsidase beta dose increased.

CONCLUSIONS

Our findings increase the limited amount of available data on long-term effects of enzyme replacement therapy in pediatric, classic Fabry patients. The low-dose regimens studied here over a period of 5 years did not demonstrate a consistent benefit among the patients in terms of controlling symptomatology, urine GL-3 levels, and pathological histology. The current available evidence supports treatment of pediatric, classic male Fabry patients at the approved agalsidase beta dose of 1.0 mg/kg 2-weekly if these patients are considered for enzyme replacement therapy with agalsidase beta.

Volumetric, Nanoscale Optical Imaging of Mouse and Human Kidney via Expansion Microscopy

Although light microscopy is a powerful tool for the assessment of kidney physiology and pathology, it has traditionally been unable to resolve structures separated by less than the ~250 nm diffraction limit of visible light. Here, we report on the optimization, validation, and application of a recently developed super-resolution fluorescence microscopy method, called expansion microscopy (ExM), for volumetric interrogation of mouse and human kidney tissue with 70-75 nm lateral and ~250 nm axial spatial resolution. Using ExM with a standard confocal microscope, we resolve fine details of structures that have traditionally required visualization by electron microscopy, including podocyte foot processes, the glomerular basement membrane, and the cytoskeleton. This inexpensive and accessible approach to volumetric, nanoscale imaging enables visualization of fine structural details of kidney tissues that were previously difficult or impossible to measure by conventional methodologies.

Heroin Use Is Associated with AA-Type Kidney Amyloidosis in the Pacific Northwest

BACKGROUND AND OBJECTIVES

AA-type kidney amyloidosis is classically associated with chronic autoimmune or inflammatory disorders. However, some urban centers have reported a high prevalence of injection drug use among patients with kidney AA amyloidosis. Previous reports lack control groups to quantify associations and most predate the opioid epidemic in the United States.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a case-control study of 38 patients with biopsy-confirmed kidney AA amyloidosis and 72 matched control individuals without this condition from two large hospital systems in Seattle, Washington. We ascertained the pattern and duration of heroin use by medical chart review and determined associations using logistic regression.

RESULTS

Among case patients, 95% had a prior history of heroin use, 87% had skin abscesses, and 76% and 27% had evidence of muscling and skin popping, respectively. After adjustment for age, race, sex, site, and year of biopsy, any heroin use (past or current) was associated with an estimated 170-times higher risk of kidney AA amyloidosis compared with no heroin use (95% confidence interval, 28 to 1018 times higher; P<0.001). Chronic autoimmune disorders were uncommon among case patients in this study. The median time to ESKD among patients with AA amyloidosis was 2.4 years (interquartile range, 0.5-7.5 years).

CONCLUSIONS

Injection heroin use is strongly associated with kidney AA amyloidosis in the Pacific Northwest. Unique aspects of heroin use, in particular geographic regions or frequent associated soft-tissue infections, may be an important cause of this progressive kidney disease.

White blood cell fractions correlate with lesions of diabetic kidney disease and predict loss of kidney function in Type 2 diabetes

BACKGROUND

Inflammation linked to diabetic kidney disease (DKD) may affect white blood cell (WBC) counts and differentials. We examined the cross-sectional associations of total WBC count and WBC fractions with structural lesions of DKD in 108 Pima Indians with Type 2 diabetes who underwent research kidney biopsies. We also examined the longitudinal association of these WBC variables with renal function loss (RFL) in 941 Europeans with Type 2 diabetes from the SURDIAGENE study.

METHODS

Associations of WBC variables with morphometric parameters were assessed by linear regression. RFL was defined as≥40% loss of estimated glomerular filtration rate from baseline. Associations with RFL were evaluated by Cox regression. Hazard ratios (HRs) were reported per standard deviation increment of each WBC variable.

RESULTS

After multivariable adjustment, lymphocyte (r  = -0.20, P = 0.043) and eosinophil (r = 0.21, P = 0.032) fractions in the Pima Indians correlated with glomerular basement membrane width. Eosinophil fraction also correlated with glomerular filtration surface density (r  = -0.21, P = 0.031). Lymphocyte fraction (r = 0.25, P = 0.013), neutrophil fraction (r  = -0.23, P = 0.021) and the neutrophil:lymphocyte ratio (r  = -0.22, P = 0.024) correlated with percentage of normally fenestrated endothelial cells. During median follow-up of 4.5 years, 321 SURDIAGENE participants developed RFL. Lower lymphocyte fraction [HR = 0.67, 95% confidence interval (95% CI) 0.60-0.76] and higher neutrophil fraction (HR = 1.35, 95% CI 1.20-1.52), total WBC count (HR = 1.20, 95% CI 1.08-1.35) and neutrophil:lymphocyte ratio (HR = 1.44, 95% CI 1.28-1.62) each predicted RFL in this cohort.

CONCLUSIONS

WBC fractions associate with morphometric lesions of DKD and predict RFL in individuals with Type 2 diabetes.