Diabetic nephropathy
Diabetic nephropathy, also known as diabetic kidney disease, is the chronic loss of kidney function occurring in those with diabetes mellitus. Diabetic nephropathy is one of the leading causes of chronic kidney disease and end-stage renal disease globally. Protein loss in the urine due to damage to the glomeruli may become massive, and cause a low serum albumin with resulting generalized body swelling and result in the nephrotic syndrome. Likewise, the estimated glomerular filtration rate may progressively fall from a normal of over 90 ml/min/1.73m2 to less than 15, at which point the patient is said to have end-stage kidney disease. It usually is slowly progressive over years.
Pathophysiologic abnormalities in DN begin with long-standing poorly controlled blood glucose levels. This is followed by multiple changes in the filtration units of the kidneys, the nephrons.. Initially, there is constriction of the efferent arterioles and dilation of afferent arterioles, with resulting glomerular capillary hypertension and hyperfiltration; this gradually changes to hypofiltration over time. Concurrently, there are changes within the glomerulus itself: these include a thickening of the basement membrane, a widening of the slit membranes of the podocytes, an increase in the number of mesangial cells, and an increase in mesangial matrix. This matrix invades the glomerular capillaries and produces deposits called Kimmelstiel-Wilson nodules. The mesangial cells and matrix can progressively expand and consume the entire glomerulus, shutting off filtration.
The status of DN may be monitored by measuring two values: the amount of protein in the urine - proteinuria; and a blood test called the serum creatinine. The amount of the proteinuria reflects the degree of damage to any still-functioning glomeruli. The value of the serum creatinine
Diabetic nephropathy is the most common cause of ESKD and is a serious complication that affects approximately one quarter of adults with diabetes in the United States. Affected individuals with end-stage kidney disease often require hemodialysis and eventually kidney transplantation to replace the failed kidney function. Diabetic nephropathy is associated with an increased risk of death in general, particularly from cardiovascular disease.
Signs and symptoms
The onset of symptoms is 5 to 10 years after the disease begins. A usual first symptom is frequent urination at night: nocturia. Other symptoms include tiredness, headaches, a general feeling of illness, nausea, vomiting, frequent daytime urination, lack of appetite, itchy skin, and leg swelling. The clinical presentation of diabetic nephropathy is characterized by proteinuria, hypertension and progressive loss of kidney function. The process may be initially indolent, making regular screening for DN in patients with diabetes mellitus of great importance.Risk factors
Not all patients with diabetes go on to develop diabetic nephropathy. The main risk factors that increase the likelihood of developing diabetic nephropathy are:- Poor control of blood glucose
- Uncontrolled high blood pressure
- Type 1 diabetes mellitus, with onset before age 20
- Past or current cigarette use
- A family history of diabetic nephropathy- certain genes have been identified that are associated with DN.
- Certain racial groups.
Pathophysiology
The pathophysiology of DN is thought to involve an interaction between hemodynamic and metabolic factors.
Hemodynamic factors include an increase in systemic and intraglomerular pressure, as well as the over-activation of the RAAS. Studies have shown that in the setting of diabetes, various factors stimulate the RAAS, which is one of the most important pathways in DN pathophysiology. Due to the higher load of filtered glucose, there is an up-regulation in the sodium-glucose cotransporter 2 in the proximal tubules, which cotransports sodium and glucose back into circulation. This leads to a decrease in the delivery of sodium chloride to the macula densa in the distal tubules, promoting the release of renin and over-activating RAAS. Hyperfiltration is one of the earliest features of DN. Several mechanisms have been proposed to cause hyperfiltration. One of these mechanisms is that as glomeruli becomes hypertrophied, filtration surface area initially increases. Another possible mechanism is that abnormal vascular control in diabetic nephropathy leads to a reduction in afferent glomerular arteriolar resistance and an increase in efferent glomerular arteriolar resistance, leading to a net increase in renal blood flow and glomerular filtration rate. Glomerular hyperfiltration and an aberrant regulation of RAAS lead to increased intraglomerular pressure, causing stress on the endothelial cells, the mesangial cells and the podocytes. This exacerbates the dysfunction caused by the metabolic effects of hyperglycemia.
Metabolic factors include the formation of advanced glycation end products, which have a central role in the pathophysiology of many of the complications of diabetes mellitus, including cardiovascular complications. AGEs are chemical groups that form when a reducing sugar reacts non-enzymatically with an amine group, predominantly lysine and arginine, which are attached on proteins, lipids and nucleic acids. These glycosylation products accumulate on the proteins of vessel wall collagen, forming an irreversible complex of cross-linked AGEs. An important way AGEs exert their effect is through a receptor-mediated mechanism, most importantly by the receptor for advanced glycation end products. RAGE is a signal transduction receptor found on a number of cell types including macrophages, endothelial cells, renal mesangial cells and podocytes in the glomerulus. Bindings of AGEs to RAGE receptors enhances production of cytosolic Reactive Oxygen Species as well as stimulates intracellular molecules such as Protein Kinase C, NF-kB and the activation of growth factors TGF-B and vascular endothelial growth factor. These factors, along with the hemodynamic changes that occur, lead to podocyte injury, oxidative stress, inflammation and fibrosis. As injury worsens, kidney function decreases and glomerular basement membrane become more permeable and less efficient at filtration. This is accompanied by a steady decline in kidney function.
Diagnosis
Diagnosis is based on the measurement of abnormal levels of urinary albumin in a diabetic coupled with exclusion of other causes of albuminuria. Albumin measurements are defined as follows:It is recommended that diabetics have their albumin levels checked annually, beginning immediately after a diagnosis of type 2 diabetes and five years after a diagnosis of type 1 diabetes. Medical imaging of the kidneys, generally by ultrasonography, is recommended as part of a differential diagnosis if there is suspicion of urinary tract obstruction, urinary tract infection, kidney stones
Urine analysis in patients with diabetic kidney disease is often bland. In cases of severely increased microalbuminuria, hematuria might be present. fat bodies might be present in patients who develop nephrotic-range proteinuria.
| CKD Stage | eGFR level |
| Stage 1 | ≥ 90 |
| Stage 2 | 60–89 |
| Stage 3 | 30–59 |
| Stage 4 | 15–29 |
| Stage 5 | < 15 |
Staging
To stage the degree of damage in this kidney disease, the serum creatinine is determined and used to calculate the estimated glomerular filtration rate. Normal eGFR is equal to or greater than 90ml/min/1.73 m2.Biomarkers
Although albuminuria is the most frequently used marker of DN, it has a limited sensitivity as many patients with DN experience GFR loss and glomerulosclerosis without immediate elevation in albuminuria. Many novel markers are currently being studied that potentially detect DN at earlier stages and identify progression risk. Cystatin C is a protein that is freely filtered in the glomeruli before it is reabsorbed and catabolized in the renal tubular cells. Its serum level is independent of muscle mass, making more accurate at estimating GFR than creatinine serum levels.Treatment
The goals of treatment are to slow the progression of kidney damage and control related complications. Management of diabetic nephropathy currently centers over four main areas: Cardiovascular risk reduction, glycemic control, blood pressure control as well as inhibition of the RAAS system.Cardiovascular risk reduction: Patients with diabetes mellitus are at significantly increased risk of cardiovascular disease, which is also an independent risk factor for kidney failure. Therefore, it is important to aggressively manage cardiovascular risk factors in patients diagnosed with DM in general and DN specifically. The main components of managing cardiovascular disease is with tobacco cessation, lipid-lowering therapies as well as regular exercise and healthy eating. In patients with kidney disease, atorvastatin is preferred over other statins as it does not require dose-adjustment based on GFR.
Glycemic control: Multiple studies have found a positive effect of improved glycemic control on clinical outcomes of patients with diabetic nephropathy. Intensive glycemic control also reduces the rate of other DM complications, such as retinopathy and neuropathy. Glycemic control is maintained mainly with insulin in patients with Type 1 DM and with hypoglycemic agents and/or insulin in patients with type 2 DM. Studies showed a decrease in microvascular complications of diabetic nephropathy with a target goal HbA1c concentration of 7%. Further reduction in the HbA1c did not correlate with better outcomes and is thus not recommended in most patients as it could increase the risk of hypoglycemic episodes.
Blood pressure control: Multiple randomized clinical trials have demonstrated a benefit of decreasing systolic blood pressure to <140 mmHg in patients with diabetic nephropathy. High blood pressure is associated with accelerated development of microalbuminuria, over proteinuria and declining kidney function. Angiotensin-converting-enzyme inhibitors, as well as angiotensin II receptor blockers, are particularly helpful in patients with diabetes to lower blood pressure and slow the progression of nephropathy. More intensive blood pressure lower in patients with diabetic mellitus has been shown to decrease the risk of progression of DN as well as other diabetic complications. Some patients might require dual therapy to adequately control pressure, in which case calcium channel blockers or diuretics are a good second-line option.
RAAS inhibition: Inhibition of the RAA system can be achieved with multiple therapies, mainly: ACE inhibitors, ARBs, direct renin inhibitors, and mineralocorticoid antagonists. RAAS inhibition has been proven to be the most effective therapy to slow the progression of diabetic nephropathy in all stages. Although RAAS blockade using more than one agent may further reduce proteinuria, the risk of adverse events outweigh the potential benefits. Therefore, it is recommended that only one agent is used in patients with DM who have hypertension or any signs of microalbuminuria or diabetic nephropathy.
About half of insulin is metabolized and cleared by the kidneys. This means that as kidney function worsens in the setting of DN, some patients with insulin-dependent DM may find that their regular insulin doses are lasting longer than normal, or that they are experiencing an increasing frequency of hypoglycemic episodes. It is also crucial to closely monitor kidney function to properly dose medications that are cleared by the kidneys. Some of the most commonly used nephrotoxic medications are non-steroidal anti-inflammatory drugs such as ibuprofen.
With worsening kidney function, it might also be necessary to follow a renal-diet to avoid complications such as hyperkalemia and metabolic acidosis. Some evidence suggests that limiting dietary protein could slow the progression of DN, but further evidence is needed to confirm this benefit. Patients with DN might go on to develop End Stage Renal Disease and might require kidney transplantation or the initiation of hemodialysis.