BACKGROUND AND AIMS
Diabetes mellitus (DM) is tightly associated with the increased prevalence and rapid evolution of diabetic nephropathy (DN). Interestingly, deterioration of kidney function in diabetic patients is often nonetheless caused by other factors besides DM and frequently goes undiagnosed. Nondiabetic renal disease (non-DRD) could be suspected in case of rapid progression of renal function impairment and/or severe, nephrotic-range proteinuria. While biopsy of the kidneys is the ‘gold standard’ of the diagnostic approach in such cases, no real consensus exists regarding the profile of diabetic patients with renal disease and proteinuria, who should be submitted to kidney biopsy. Thus, this study intends to correlate the clinical and biochemical profile of diabetic patients with deteriorated kidney function to the histopathological data of a kidney biopsy and allows early differentiation between DN and non-DRD based on the results of kidney biopsy.
METHOD
A total of 32 patients, who were treated in our outpatient's diabetes clinic from a multidisciplinary team of endocrinologists and nephrologists at Evangelismos General Hospital, were retrospectively studied. All patients suffered from DM2 and presented with nephrotic-range levels of proteinuria. Biochemical data of glycemic control and renal function, clinical findings related to DN and histological findings of kidney biopsy were documented. All patients were submitted to kidney biopsy and depending on the histopathologic findings were categorized into three groups: (i) genuine diabetic nephropathy (GDN), (ii) renal disease due to cause other than diabetes mellitus (ODMRD) and (iii) mixed renal disease (MRD).
RESULTS
Among the 32 patients, 15 (46.9%) had findings of a GDN, while 17 patients (53.1%) suffered from ODMRD (13 patients) or MRD (4 patients). All patients were hypertensive. The patients with GDN were younger (54.1 versus 68.2 versus 70.5 years, P = 0.016) and had a higher HbA1C value (7.9 versus 6.5 versus 6.8%, P = 0.069) at the time of the kidney biopsy in comparison to the ODMRD and MRD patients. On the contrary, ODMRD patients had significantly smaller disease duration compared with the GDN and MRD groups (8.4 versus 11.6 versus 13.3 years, P = 0.04). Furthermore, the incidence of diabetic retinopathy was greater among patients with GDN and MRD in comparison to the ODMRD patients (60 versus 75 versus 7.6%, P < 0.01). Additionally, interstitial fibrosis was significantly more prevalent among the patients with GDN in comparison to those with ODMRD and MRD, respectively (73.3 versus 38.4 versus 50%, P = 0.02). Finally, the presence of diabetic retinopathy {OR 4.88, [95% confidence interval (CI) 1.06–22.38], P = 0.04}, higher levels (>25%) of interstitial renal fibrosis [OR 5.71 (95% CI 1.16–28.1), P = 0.032] and longer DM2 duration (>10 years) [OR 5.04, (95% CI 1.1–22.96), P = 0.036] were recognized as factors, which were positively associated with GDN.
CONCLUSIONS
This study highlights emphatically the usefulness of the kidney biopsy and its histopathological findings in case of patients with diabetes mellitus and nephrotic-range levels of proteinuria. The value of a detailed and careful medical history seems to be critical for the early diagnosis of the type of kidney disease in diabetic patients. It is crucial to early differentiate the patients who suffer from nondiabetic nephropathy, from those with diabetic nephropathy and initiate the appropriate therapy, according to the underlying cause. Thus, the detection of nephrotic-range levels of proteinuria in diabetic patients should lead to kidney biopsy especially in case diabetic retinopathy is not present and longer disease duration is observed. Finally, the existing criteria/indications for a kidney biopsy in diabetic patients with nephrotic-range levels of proteinuria should be reconsidered or even revised.
