Kidney biopsy findings linked to recovery after severe AAV kidney injury

Kidney biopsy findings may help identify which adults with severe kidney involvement due to ANCA-associated vasculitis (AAV) are more likely to recover kidney function after treatment, a small study suggests.

Data showed that patients with better kidney function at one year had a higher percentage of normal glomeruli — the kidneys’ tiny filtering units — and tended to have less glomerulosclerosis, or scarring of the glomeruli, at the time of biopsy.

“These results may suggest the benefit of performing systematic kidney biopsies in severe AAV kidney injury to assess the evolution of kidney function in these patients and better guide their follow-up and intensity of treatment,” the researchers wrote.

The study, “Kidney histopathology associated with kidney function at 1 year post severe AKI related to ANCA-associated vasculitis,” was published in BMC Nephrology.

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Severe kidney involvement is common in AAV

AAV is a group of autoimmune diseases marked by inflammation and damage to small blood vessels. Most cases are caused by self-targeting antibodies called ANCAs. The kidneys are commonly affected, typically resulting in rapidly progressive glomerulonephritis, or inflammation of the glomeruli. Kidney involvement is often linked to poorer outcomes.

Treatment for severe AAV typically includes corticosteroids and immunosuppressive medications such as cyclophosphamide or rituximab. Tavneos (avacopan) may be used alongside those immunosuppressive treatments. Plasmapheresis also has been used in severe cases, although its benefits remain debated.

Because the severity of kidney disease can vary widely at diagnosis, current guidelines recommend a kidney biopsy, the collection of a small tissue sample for examination under a microscope, when there are no contraindications. A biopsy can help confirm the diagnosis and assess the level of active inflammation and permanent scarring in kidney tissue.

Here, a team of researchers in France sought to identify kidney biopsy features that may help assess which people with severe AAV-related kidney injury are more likely to recover kidney function after at least three plasmapheresis sessions and immunosuppressive treatment.

To do this, they reviewed data from 34 adults with severe kidney injury due to AAV who were treated at two hospitals between January 2008 and December 2020. The participants had a median age of 67, and 56% were men. All had one of the two most common types of AAV, granulomatosis with polyangiitis or microscopic polyangiitis, or AAV limited to the kidneys.

At diagnosis, median blood creatinine levels — a marker used to assess kidney function — were very high, indicating severe kidney impairment. More than half of the participants (64.7%) required kidney replacement therapy, such as dialysis.

Patients underwent a kidney biopsy within two weeks of admission. Treatment included plasmapheresis, with a median of seven sessions, and intravenous corticosteroids followed by oral corticosteroids, either alone or combined with cyclophosphamide or rituximab.

Researchers then divided patients into two groups based on their kidney outcomes at one year. The less favorable outcome group included patients who required dialysis, had persistent severe kidney dysfunction — defined as an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m² for three months — or died with persistent kidney dysfunction. Patients in the better outcome group had an eGFR above 30 mL/min/1.73 m² and did not require dialysis.

Biopsy findings differed by kidney outcome

At one year, 19 patients (55.9%) showed a less favorable kidney response. The remaining 15 patients (44.1%) had an eGFR above 30 mL/min/1.73 m² at one year and were not on dialysis, representing the better kidney response group.

The group with better kidney recovery had a significantly higher median percentage of normal glomeruli on kidney biopsy (25% vs. 11.6%) and a significantly lower median percentage of abnormal glomeruli (75% vs. 88.4%). The median percentage of glomerulosclerosis was higher in the less favorable outcome group (22.2% vs. 15.4%), but the difference did not reach statistical significance.

The less favorable kidney outcome group also had numerically higher median percentages of fibrocellular crescents (22.2% vs. 9.1%), fibrous crescents (5.6% vs. 0%) and circumferential crescents (42.9% vs. 36.4%) than the better outcome group, although none of these differences was statistically significant. Crescents are abnormal structures that can form in glomeruli during severe inflammation.

None of the patients with favorable outcomes were in the sclerotic class of the Berden classification, a category marked by extensive kidney scarring.

The ANCA Renal Risk Score, which estimates the risk of kidney failure, was higher in the less favorable outcome group, but the difference was not statistically significant. Two other measures — the ANCA Kidney Risk Score and the GFEV score — were similar between the groups.

Overall, the findings suggest that a higher percentage of normal glomeruli — and possibly a lower percentage of glomerulosclerosis — may help identify adults with severe AAV-related kidney injury who are more likely to recover kidney function.

“These results could support the systematic use of kidney biopsies for severe forms of ANCA-associated vasculitis, to better adapt treatments,” the team wrote, adding that prospective, randomized studies are needed to determine whether kidney biopsy findings can help guide individualized treatment.