© F e r r a t a S t o r t i F o u n d a t i o ntent interstitial lymphocytic infiltration was observed. Standard processing of kidney biopsies evaluated at the Mayo Clinic included light microscopy, immunofluorescence, and electron microscopy. For light microscopy, biopsy specimens were stained with hematoxylin-eosin, periodic acid Schiff, Masson trichrome, and Jones methenamine silver. For immunofluorescence, 3-micron cryostat sections were stained with polyclonal fluorescein isothiocyanate-conjugated antibodies to IgG, IgM, IgA, C3, C1q, kappa and lambda light chains, fibrinogen, and albumin (Dako), as per routine clinical testing. Electron microscopy was performed as per clinical routine.Immunohistochemical stains for CD3, CD5, CD20, and CD23 were done in cases of interstitial lymphocytic infiltration (and for PAX5 and CD19 in selected cases) to help assess CLL/SLL involvement. Renal biopsy findings were further classified according to a potential causal relationship with CLL. Cases of membranoproliferative glomerulonephritis (MPGN), CLL infiltrate as primary etiology, minimal change disease (MCD), acute interstitial nephritis, amyloidosis, light chain cast nephropathy, membranous glomerulonephritis, and unclassified mesangial proliferative glomerulonephritis were considered directly related to CLL. Cases secondary to CLL-associated conditions, such as infections, autoimmune disease, and other cancers, or CLL treatment were considered potentially indirectly related to CLL. Cases secondary to non-CLL associated comorbidities or non-CLL treatment, such as diabetes, hypertension or obesity, were considered unrelated to CLL.
Statistical analysisDescriptive statistics of baseline characteristics were calculated. The Mann-Whitney test was used for comparisons of medians. Overall survival was defined as time from diagnosis to death or last follow up. Survival curves were calculated using the Kaplan-Meier method, and comparisons were made using the log-rank test. All P-values were two-sided and considered statistically significant if ≤0.05. Statistical analyses were completed using SPSS 21.
Results
Baseline characteristicsBetween January 1 st , 1995 and June 30 th , 2014, 4,024 patients with CLL, SLL or MBL were followed at our institution. Of these patients, 49 (1.2%) had an ultrasound-guided kidney biopsy during follow-up to evaluate renal failure and/or nephrotic syndrome. Of these biopsies, 10% were performed before 2005, 49% between 2005 and 2010, and 41% after 2010. The indication for renal biopsy was renal insufficiency (without evidence of post-renal compression or tumor lysis) in 34 patients (69%; median creatinine 3.2 mg/dL, range 1.7-15) and nephrotic syndrome in 15 (31%; median proteinuria 11.3 g/24 hours, range 4-54.9). The pertinent baseline characteristics of these 49 patients at the time of CLL diagnosis are shown in Table 1.Kidney biopsy results are shown in Table 2. The distribution of renal pathology based on the indication for biopsy is shown in Figure 1. Of interest, among the five patie...