Renal outcomes in patients with type 2 diabetes with or without coexisting non-diabetic renal disease
Introduction
Diabetic nephropathy is the leading cause of end-stage renal disease (ESRD) worldwide, and its prevalence is strikingly rising mainly due to a recent significant increase in the number of type 2 diabetic patients [1]. Even though diabetic nephropathy is rarely diagnosed by renal biopsy in patients with diabetes of short duration, the diagnosis is usually made based on clinical features in the context of longstanding diabetes mellitus with target organ damage, such as retinopathy or neuropathy, and proteinuria preceding azotemia. This kind of clinical approach has clearly been validated in patients with type 1 diabetes, but has not been as well verified in type 2 diabetic patients. In patients with type 1 diabetes of more than 10 years, especially when diabetic retinopathy or neuropathy is accompanied, proteinuria is usually a manifestation of diabetic nephropathy, which is histologically proven in >95% of patients [2], [3], [4]. In these patients, therefore, renal biopsy is not mandatory for diagnosis. However, in type 2 diabetic patients, a more heterogeneous pattern of renal lesions has been demonstrated, suggesting that a possibility of non-diabetic renal diseases (NDRD) should always be considered in patients with type 2 diabetes [5]. Reports on the prevalence of NDRD in type 2 diabetic patients have varied widely from 12 to 81% [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. This variation may be due to the fact that most of the NDRD in type 2 diabetic patients has been diagnosed by renal biopsy based on variety of indications.
On the other hand, it is well known that the pathological changes of diabetic nephropathy are almost always irreversible, while some forms of NDRD, such as minimal change disease, membranous nephropathy, and acute interstitial nephritis, are often treatable or even remittable [19]. Since the treatment and prognosis of diabetic nephropathy and NDRD are quite different, discernment of NDRD from diabetic nephropathy is of considerable importance. Previous studies have revealed several conducive clinical and laboratory findings that can be used to discriminate between the two [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Nevertheless, the results were not uniform, likely due to differences in the study populations and selection criteria. Moreover, the influence of NDRD on renal outcomes in type 2 diabetic patients has not been well established, and most of the available data have been retrieved from cross-sectional studies [20], [21], [22], [23], [24], [25]. In this study, therefore, we not only sought to determine the independent predictors of NDRD but also to investigate the impact of NDRD on renal outcomes in patients with type 2 diabetes who underwent renal biopsy and were followed-up longitudinally.
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Patients
The present study was conducted by reviewing the medical records of 138 type 2 diabetic patients who underwent percutaneous renal biopsy at Yonsei University Health System from January 1988 to December 2008. All patients were diagnosed as type 2 diabetes, as defined by the World Health Organization and the American Diabetes Association, with the absence of ketosis-prone state (absence of significant ketonuria and insulin treatment started at least 1 year after diagnosis) [26], [27]. Among the
Patient profiles and pathologic findings
A total of 119 patients with a mean follow-up duration of 40.2 ± 44.2 months were included in the present study. The mean age of the patients at the time of renal biopsy was 53.1 years (range 34–80 years). Sixty-four patients (53.8%) were male, and the mean duration of diabetes prior to renal biopsy was 95.5 ± 76.3 months. The prevalence of hypertension, diabetic retinopathy, hematuria, and proteinuria (≥300 mg/24 h) at the time of renal biopsy were 64.7%, 42.9%, 54.6%, and 95.0%, respectively. The
Discussion
In this study, renal biopsy findings showed that diabetic nephropathy was present in less than one-half of patients (group I and II), whereas 63.9% of type 2 diabetic patients had NDRD (group II and III). Since renal biopsy in patients included in our study was performed with a strong suspicion of NDRD, we infer that biases in selecting patients may contribute to this high prevalence of NDRD.
Since specific treatments for NDRD are often necessary in diabetic patients with NDRD, it is of great
Conflicts of interest
There are no conflicts of interest.
Acknowledgements
This work was supported by the BK21 (Brain Korea 21) Project for Medical Sciences, Yonsei University, the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (R13-2002-054-04001-0), and a grant of the Korea Healthcare Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea (A084001).
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