Background/Purpose:

The most common and clinically and histologically
best-characterized SLE kidney disease is lupus nephritis (LN).  However, other
forms of kidney disease can and do occur concomitantly with LN, although their
prevalence, clinical features and impact on disease course and response to
therapy are not well described. We sought to determine the prevalence of other concomitant
kidney pathology among patients with newly diagnosed LN, and to compare
demographic and clinical features between patients with and without concomitant
kidney findings.

Methods:

We identified patients age ≥18 years with ≥1
visit for LN and a kidney biopsy reviewed at our large academic hospital from
1992 to 2014. (For those with > 1 biopsy, we analyzed only the first) We ascertained demographics,
clinical factors, and reviewed kidney biopsy reports for International Society
of Nephrology/Kidney Pathology Society class (ISN/RPS) and concomitant
findings. We calculated the prevalence of concomitant kidney diseases in this
group of LN patients. Data were stratified by the type of kidney disease and
analyzed to determine demographics, classification of lupus nephritis,
median activity and chronicity index, HIV and antiphospholipid antibody status
before or at the time of kidney biopsy. To compare those with and without
concomitant kidney disease, Fisher’s exact tests were used for categorical
variables and Wilcoxon rank-sum tests for continuous variables.

Results:

We identified 76 patients with LN confirmed on kidney
biopsy. Overall, the median age at biopsy was 37 years old (range 18-71) and
racial breakdown was: Asian 6%, Hispanic 16%, Black 25%, White 29%,
other/unknown 23%. The major concomitant kidney pathologic findings were
thrombotic microangiopathy (TMA, 10, 13%) and collapsing glomerulonephropathy
(GN, 15, 20%). Four patients (5%) had both TMA and collapsing GN. Comparisons
of the demographic and clinical factors among those with and without
concomitant kidney disease are given in the Table. Compared to those
without concomitant pathology, patients with collapsing glomerulonephropathy
and those with TMA were more likely to be Black (Table).  Distributions
of lupus nephritis class were different across the 3 groups defined by presence
of collapsing GN or TMA or not, but there were no significant differences in
median activity or chronicity indices. No patients were HIV positive. There
were no differences in the proportions who had antiphospholipid antibodies.
Other findings included interstitial nephritis (6, 8%), tubular injury (5, 7%)
and vascular injury (10, 13%).

Conclusion:

Other concomitant pathology occurred in a substantial number
of LN kidney biopsies in this population. The clinical and prognostic
implications of these findings deserve further study. In future analyses, we
will investigate variation in treatment and outcomes among those with and
without other concomitant kidney pathologies.