#2168 Lupus nephritis histopathological classification system: a questionnaire-based survey of the Renal Pathology Society (RPS)
Authors: Uzzo Martina , Haas Mark , Jayne David R W , Lightstone Liz , Parodis Ioannis , Rovin Brad , Seshan Surya V , Akilesh Shreeram , Fogo Agnes , Bajema Ingeborg 
Published: May 2024

Abstract

Background and Aims
Kidney biopsy is the gold standard for lupus nephritis diagnosis, defining histologic class, disease activity and chronicity in detail and providing guidance for treatment. The updated 2018 ISN/RPS histopathological classification in lupus nephritis is widely used for prognosis and treatment decisions. Given the evolving phenotypes of lupus nephritis and the success of new targeted agents in clinical trials, there is ongoing discussion about the need for updating existing classification systems. A survey to assess the current use of the lupus nephritis histopathological classification systems in everyday practice was conducted on behalf of the RPS.

Method
An online survey was sent between September 27th and October 24th, 2023 to active members of the RPS. The survey used an internet platform and contained both multiple-choice and open-ended questions; results were analyzed anonymously.

Results
185 of 562 RPS members replied to the questionnaire. 179 (97%) were pathologists and the level of expertise in lupus nephritis was good: 120 (65%) participants indicated they encounter more than 20 biopsies with lupus nephritis per year, while only 13% encounter fewer than 10.
Almost 90% of responders discuss kidney biopsy results in a multidisciplinary meeting involving both clinicians and pathologists, on a weekly or monthly basis. The 2018 ISN/RPS lupus nephritis classification is used in most cases (92%), while 7% of participants prefer the earlier 2004 version. The average grade on the utility of the 2018 ISN/RPS classification was 8 (IQR 7-9) on a scale from 0 (not useful) to 10 (extremely useful).
Almost 90% of the pathologist responders indicated they include the NIH activity/chronicity indices in biopsy reports. Reasons for not adding the activity/chronicity indices were given as responses to open-ended questions: (1) clinicians usually do not ask for activity/chronicity indices—(2) the extra workload outweighs the perceived clinical benefit—(3) a quantitative description of the degree of activity/chronicity is less time-consuming and more understandable than the indices—(4) reproducibility is not guaranteed. The average grade on the utility of the activity/chronicity indices was 7 (IQR 7-9) on a scale from 0 (not useful) to 10 (extremely useful).
Pathologists rated treating clinicians' understanding of kidney biopsy reports and lupus classification at light microscopy with an average score of 8 (IQR 7-9) on a scale from 0 (no understanding) to 10 (complete understanding). Suggested improvements of the 2018 ISN/RPS lupus nephritis classification were further standardization and simplicity. Clearer definitions were requested for: class III vs class IV; segmental sclerosis vs fibrotic crescents; the role of globally sclerosed glomeruli; lupus-like entities; and lupus podocytopathy. Furthermore, there was a request on guidelines for new parameters: e.g., focus on extraglomerular involvement, laboratory and clinical features and biomarkers; CD68+ staining to detect endocapillary hypercellularity; and EXT1/2 immunostaining.

Conclusion
Our survey shows the 2018 ISN/RPS lupus nephritis classification is widely used in everyday practice by pathologists, and well known by clinicians. The results obtained by the RPS survey serve as a starting point for the new Working Group of lupus nephritis classification. We will consider the ideas and suggestions of the international community to evaluate biopsies from extensively phenotyped cohorts, to modify the classification and to facilitate improved targeted treatment decisions—a current unmet need.