Predictive power of the second renal biopsy in lupus nephritis: significance of macrophages.

BACKGROUND

A new Biopsy Index containing the Glomerular Activity (GAI), Tubulointerstitial Activity (TIAI), Chronic Lesion (CLI), and Immunofluorescence (IFI) indices was developed, showing better correlations with clinical and outcome parameters than the National Institutes of Health Activity and Chronicity Indices (AI and CI) in lupus nephritis. This report examines the ability of these indices and individual morphologic variables to predict doubling of serum creatinine (SCr; CRX2).

METHODS

Renal biopsies from 71 patients with lupus nephritis with an initial biopsy (Bx1) and systematic control biopsy (Bx2) after six months of therapy were studied. Kaplan-Meier survival curves were developed for each index and morphologic variable at each biopsy. A subset of 30 biopsies was stained with the macrophage marker PGM1.

RESULTS

At Bx1, only the TIAI and the quantity of C3 and vascular staining on IF were predictive of CRX2. At Bx2, particularly predictive of CRX2 were the GAI, IFI, Biopsy Index, and BxInfl, a composite variable comprised of all of the inflammatory variables. Among individual variables, glomerular and tubular macrophages correlated the best with clinical and outcome parameters. Crescents and karyorrhexis/fibrinoid necrosis also correlated with outcome. Neither the NIH CI or our CLI, nor the TIAI correlated with outcome. In 30 biopsies stained with PGM1, PGM1+ cells correlated well with glomerular and tubular macrophages identified on routine stains and showed even better correlations with SCr, proteinuria, and progression to renal insufficiency than the latter. A diffuse membranoproliferative (MPGN) pattern was seen in seven patients at Bx1. In four of the seven patients, MPGN disappeared with therapy, and all finished with normal renal function. However, among the three patients in whom MPGN persisted and eight patients in whom MPGN, focal or diffuse, appeared under therapy, six reached end-stage renal disease, and a seventh died with marked renal insufficiency.

CONCLUSIONS

The biopsy index and its components correlate modestly with CRX2 at Bx1, but strongly at Bx2, particularly IFI, BxInfl, and glomerular and tubular macrophages. Stains for macrophage markers form a valuable adjunct in interpretation of renal biopsies in systemic lupus erythematosus (SLE). MPGN features do not have an ominous significance at Bx1, but their persistence or appearance under therapy are associated with poor outcome.