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Diagnosis: Mesangial proliferative lupus nephritis, class II

In the new International Society of Nephrology / Renal Pathology Society (ISN/RPS) classification schema of lupus nephritis (2004), class II is defined as purely mesangial hypercellularity of any degree and/or mesangial matrix expansion by light microscopy, with mesangial immune deposits. There may be rare isolated subepithelial or subendothelial deposits by immunofluorescence or electron microscopy that are not visible by light microscopy. In the original WHO classification (1982, modified in 1995), class II had been subdivided into class IIa and IIb according to the absence or presence of mesangial hypercellularity, respectively. In the ISN/RPS classification, the original WHO class IIa has now become class I and the original WHO class IIb has become class II.

The mesangial proliferation is usually mild to moderate. It may be focal or diffuse and may be segmental or global. Variable increase in mesangial matrix may accompany the mesangial hypercellularity. Usually, the mesangial deposits are not large enough to be identified by light microscopy, but in some cases, as the present case, large mesangial deposits expand the mesangium and may be see with light microscopy, with a good trichrome staining (Figures 5 and 6).

Immunofluorescence reveals immune deposits of IgG and, more variably, IgM, IgA, C3, and C1q outlining the mesangial axis, with sparing of the peripheral glomerular capillary walls.

The renal manifestations of class II lupus nephritis are mild, fewer than 50% of patients have mild hematuria or proteinuria (usually <1g(24h). The nephrotic syndrome is very infrequent; renal insufficiency is also uncommon. Despite the relatively mild glomerulonephritis, serologic tests for SLE may be strongly positive (D'Agati VD. Renal disease in systemic lupus erythematousus... In Jennette JC et al. (Eds): Heptinstall's Pathology of the Kidney, 6th ed. Wolters Klumer / Lippincott Williams & Wilkins, Philadelphia, 2007, pp.517-612).

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Bibliography

• Markowitz GS, D'Agati VD. The ISN/RPS 2003 classification of lupus nephritis: an assessment at 3 years. Kidney Int. 2007 Mar;71(6):491-5. [PubMed link]
• Weening JJ, D'Agati VD, Schwartz MM, Seshan SV, Alpers CE, Appel GB, Balow JE, Bruijn JA, Cook T, Ferrario F, Fogo AB, Ginzler EM, Hebert L, Hill G, Hill P, Jennette JC, Kong NC, Lesavre P, Lockshin M, Looi LM, Makino H, Moura LA, Nagata M. The classification of glomerulonephritis in systemic lupus erythematosus revisited. J Am Soc Nephrol. 2004 Feb;15(2):241-50. [PubMed link] [Free full text]
• Tam LS, Li EK, Lai FM, Chan YK, Szeto CC. Mesangial lupus nephritis in Chinese is associated with a high rate of transformation to higher grade nephritis. Lupus. 2003;12(9):665-71. [PubMed link]

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