Thread by @arkanalabs

Time for another #DiseaseWeek tweetorial. How do we classify lupus nephritis?

The International Society of Nephrology and RPS created an LN classification system consisting of 6 classes of disease based on morphologic findings on kidney biopsy. A simplified view is below. /1

The classes are based on the distribution of immune deposits and the proportions of glomeruli affected. This classification is VERY glomerulocentric. #DiseaseWeek /2

Here's an overview of the classification of lupus nephritis. #DiseaseWeek /3

In class I (minimal mesangial) lupus nephritis, mesangial immune complexes are identified by immunofluorescence without any significant changes by light microscopy. IgG deposits are necessary, but there is sometimes not 'full house' staining. #DiseaseWeek /4

'Full house' staining is when there are all 3 immunoglobulin heavy chains (IgA, IgG, and IgM) and both complement components routinely stained for (C3 and C1q), along with light chains lighting up on kidney biopsy. #DiseaseWeek/5

In class II (mesangial proliferative) lupus nephritis, mesangial immune complexes are present by immunofluorescence with mesangial expansion and mesangial hypercellularity by light microscopy. #DiseaseWeek /6

Class III and IV LN show proliferative changes within glomeruli. In class III LN (focal lupus nephritis), less than 50% of glomeruli show proliferative lesions. In class IV LN, greater than 50% of glomeruli contain proliferative changes (diffuse lupus nephritis). #DiseaseWeek /7

Focal (class III) or diffuse (class IV) lupus nephritis can have concurrent subepithelial deposits.

If >50% of the glomerular capillary loops are involved, there is concurrent membranous LN (class V LN). We'll dive more into membranous lupus nephritis tomorrow. #DiseaseWeek/8

If there are subepithelial IgG deposits without proliferative lesions, there is a 'pure' membranous lupus nephritis (class V). #DiseaseWeek/9

When there is glomerular immune deposition with >90% of glomeruli being globally sclerotic, there is advanced sclerosing lupus nephritis (class VI), of which is end-stage kidney disease due to lupus. #DiseaseWeek/10

Let's do another #DiseaseWeek challenge question! Which of the following lupus classifications can be seen in the same biopsy? /11

The answer is (D), ISN/RPS class III + V. Concurrent membranous LN (ISN/RPS class V) can be diagnosed with proliferative LN (class III or IV) if >50% of the glomerular capillary loops in >50% of glomeruli show subepithelial and/or intramembranous IgG deposits. #DiseaseWeek /12

Tune in tomorrow as we continue #DiseaseWeek with a discussion of the NIH activity and chronicity indices to evaluate lupus nephritis! /13