Definition

 • Immune complex GN related to SLE with glomerular deposition of immune complexes.

 Epidemiology

 • up to 40% of patients with SLE will develop renal involvement. Renal involvement is usually indicated by the presence of haematuria, proteinuria or decreased renal function, and requires a renal biopsy for confirmation

 • Can develop in patients with known SLE, or be the first manifestation of SLE.

Aetiology

• Circulating immune complexes deposit in the kidney, lead to complement activation and glomerular inflammation.

 • The pattern of glomerular involvement depends on where the immune complexes deposit.

Typical pathological features

• Lupus nephritis can cause a number of changes in the glomeruli, ranging from mild mesangial hypercellularity to global glomerular hypercellularity. Secondary FSGS may be present. In severe cases, there are crescents and necrosis of the glomerular tuft. In some cases, the immune complex deposits are so large they can be seen on light microscopy along the capillary walls (‘wire- loop’) and/ or within capillary lumens (‘hyaline thrombi’) (Fig. 1).

Fig1. Lupus nephritis showing endocapillary hypercellularity (star), hyaline thrombi within capillary loops (thick arrows) and ‘wireloops’ (thin arrow) along a capillary wall (see Plate 25).

• Patterns of involvement are classified using the Renal Pathology Society/ International Society of Nephrology Lupus Nephritis classification (Table 1).

 • Immunofluorescence: most often there is a ‘full house’ deposition of IgG, IgA, IgM, C3, and C1q, although other patterns can be observed. The presence of C1q indicates activation of the classical pathway of complement activation and its presence in a GN must always raise suspicion for lupus nephritis.

 • Electron microscopy: electron- dense immune deposits are present. Their distribution depends on the pattern of involvement. Presence of at least a small number of deposits in all three sites (mesangial, subendothelial, and subepithelial) is typical and when noted must always raise suspicion for lupus nephritis.

 • SLE can also lead to renal pathologies other than GN: lupus podocytopathy resembles MCD; SLE is a cause of active TIN and can be associated with immune complex deposits within the tubular basement membrane; arteries can show involvement by immune complex deposits (lupus vasculopathy) or vasculitis (necrotizing arteritis).

Prognosis

• 10– 20% of patients progress to end- stage renal failure within 5 years of diagnosis of lupus nephritis.

• With adequate treatment, remission is achieved in about 50– 70% of patients, but relapses occur.

• The RPS/ ISN Classification of Lupus Nephritis documents 6 types of glomerular involvement (see Table 1). Proliferative lupus nephritis (classes III and IV) have a worse outcome.

• As for other renal diseases, persistent proteinuria, increased creatinine, and hypertension are clinical features of poor prognosis.

 • In addition to the class system, activity and chronicity indices are given to quantify changes in lupus nephritis. The activity index relates to extent of ‘active’, potentially treatable lesions (endocapillary hypercellularity, karyorrhexis, ‘wire loops’, and hyaline thrombi, cellular crescents, fibrinoid necrosis, interstitial inflammation), and the chronicity index indicates the extent of chronic, likely irreversible lesions (global and segmental scarring, fibrous crescents, and tubular atrophy/ interstitial fibrosis).

Table 1. Renal Pathology Society/ International Society of Nephrology Lupus Nephritis classification