Kidney Disease in Obese Patients: A 12 Year Renal Biopsy Study
Steven P Salvatore, Surya V Seshan. Weill Cornell Medical College, New York, NY
Background: Renal biopsies are performed in obese patients with clinical renal disease which may be directly related to obesity or secondary to associated or unassociated medical conditions. Obesity related glomerulopathy (ORG) is a pathologic process attributed to hyperfiltration podocyte injury in which glomerular hypertrophy, perihilar segmental sclerosis, and partial foot process effacement lead to subnephrotic proteinuria in patients with excess body mass.
Design: Native kidney biopsies from 2000 to 2012 were retrospectively reviewed from patients with obesity, defined as body mass index greater than 30kg/m2. 32 cases were excluded including those with less than 5 glomeruli. Glomerular diameter was measured using a standard micrometer in 1-7 glomeruli (mean 4) in glomeruli cut through the hilum. The clinicopathologic characteristics are analyzed.
Results: Of 6702 total native kidney biopsies, 287 (4%) were obtained from obese patients (mean: weight 122kg [range: 74-236kg], BMI 40.3kg/m2 [range: 30-66.5]). Associated factors such as insulin resistance (31%, n=80), hypertension (60%, n=153), and obstructive sleep apnea (9%, n=22) were also frequent. The main indication for biopsy was proteinuria in 93% (n=237), nephrotic (102) and subnephrotic (135). Of these patients, 52% (n=123) also had renal insufficiency, defined as Cr >1.5mg/dL. Typical lesions of ORG were seen in 41% of cases: focal segmental glomerulosclerosis (FSGS) 28% (n=72) - perihilar variant (n=22), and glomerulomegaly alone 13% (n=33). Of patients without hypertension or diabetes, glomerulomegaly alone was the most common finding in 44% (n=8/18). Diabetic nephropathy was seen in 22% (n=56) of all obese patients and 70% of the obese diabetic patients, immune complex disease 15% (n=39), tubulointerstitial diseases 5%, vascular diseases 5%, thin basement membranes 5%, minimal change disease 3%, idiopathic FSGS 2%, and collapsing glomerulopathy 2% with varying tubulo-interstitial scarring and vascular sclerosis. Glomerulomegaly as defined by glomerular diameter greater than 180 μm was present in 84% (n=215) of cases (mean 224+/- 34 μm), borderline in 4% (n=10), and of normal size in 11% (n=29) (mean 157 +/- 15 μm).
Conclusions: Obese patients may have multiple comorbidities contributing to renal injury and the development of proteinuria. Presumably hyperfiltration-induced glomerular hypertrophy was seen in 84% of cases, which may contribute towards podocyte injury and proteinuria regardless of underlying disease. Kidney biopsy is important for accurate diagnosis and potentially guiding therapy in this difficult patient population.
Category: Kidney (does not include tumors)
Tuesday, March 5, 2013 9:00 AM
Proffered Papers: Section H, Tuesday Morning