Nephrotic syndrome is a rare disease, but why is it important?
- It is the major cause of referral cases to higher levels.
- Chronic condition
- Complexity in evaluation
- Its complexity in management
Nephrotic syndrome is not a disease in itself but is an important feature of several kidney diseases.
The main characteristics are:
- Marked proteinuria >3.5 g/day
- Generalized edema
The key component is proteinuria which is due to a disorder of glomerular permselectivity. All other components are secondary to the protein leakage in the urine
A normal kidney has about 1.2 million nephrons
The glomerular structure has
- Fenestrated endothelium
- Glomerular basement membrane
The glomerular has two types of barriers: Size barrier and negative charge barrier
Usually, the glomerulus only lets small molecules such as sodium and water to pass through to urine
In Nephrotic syndrome, the glomeruli are damaged and become more permeable therefore letting plasma proteins to leak into urine. This causes proteinuria typically greater than 3.5 g/day
Classification of nephrotic syndrome
Nephrotic syndrome can be primary, being a disease specific to the kidneys, or it can be secondary, being a renal manifestation of a systemic general illness.
- Minimal-change nephropathy
- Focal glomerulosclerosis
- Membranous nephropathy
- Hereditary nephropathies
- Diabetes mellitus
- Streptococcus group A beta-hemolytic
- Viral infections (e.g., hepatitis B, hepatitis C, human immunodeficiency virus [HIV] )
- Amyloidosis and paraproteinemias
- Connective diseases such as systemic lupus erythematosus.
- Malignancies ie Hodgkin's disease.
- Allo-antibodies from enzyme replacement therapy.
- Drugs like heavy metal poisoning with mercury.
There is a need to rule out the possible causes before the disease as an idiopathic nephrotic syndrome by a good history taking and physical examinations together with laboratory investigations
Pathophysiology of glomerular protein leakage
Plasma protein larger than 70 nm is restricted from passing through the glomerular basement membrane by a charge – size-selective barrier.
Charge selective barrier -Polyanionic glycosaminoglycans, eg heparan sulfate in the glomerular basement membrane restrict the passage of small polyanionic plasma proteins (70-150 kd) such as albumin. There is a loss of charge selectivity in minimal change glomerulonephropathy.
In patients with FSGS, a plasma factor known as the Savin factor is produced by lymphocytes and increases glomerular basement membrane permeability.
Albumin is the main protein lost because it is the most common and is the smallest of the plasma proteins. When there is loss of charge selectivity like neutralization of the charges in minimal change glomerulonephropathy the albumin can leak out to urine causing hypoalbuminemia or low albumin levels in blood and albuminuria
Is proteinuria harmful?
Loss of albumin causes lowering of plasma oncotic pressure as a result, the extracellular fluid starts to seep out of the intravascular compartment causing hypovolemia. Hypovolemia leads to lowered kidney perfusion stimulating the activation of the Renin-angiotensin-aldosterone system.
RAAS system then enhances distal renal tubular sodium reabsorption. And since fluid cannot be held within the vascular compartment it leaks out to the tissues leading to development of pitting edema.
In severe cases, hypoalbuminemia can cause hypovolemia with pre-renal failure
This leads to loss of small-sized proteins in the urine such as immunoglobulins like IgG and factor B causing alternate pathway of complement activation to be compromised. This leads to low immunity to infections.
Proteinuria also causes loss of thyroxine-binding proteins, 25 OH cholecalciferol-binding globulin and transferrin leading to impaired iron transportation that causes iron deficiency anemia
Proteinuria also leads to loss of antithrombin III in the urine. Fibrinogen is a big molecule and not lost in urine therefore there are high levels of fibrinogen in serum
Higher levels of fibrinogen in serum causes hypercoagulation of blood. Thus nephrotic syndrome is a hypercoagulable status. The risk of thrombosis is increased by hyperviscosity of the blood.
There is also increased hepatic synthesis of cholesterol, triglycerides and lipoproteins known as Hyperlipidemia. There is also increased urinary loss of high-density lipoproteins (lipuria).
Long-standing proteinuria may cause interstitial disease
Edema of nephrotic syndrome
Hypoalbuminemia leads to low oncotic pressure in the intravascular compartment. This in turn causes a change in Starling equilibrium and extracellular fluids leaks from the intravascular compartment to the interstitial compartment.
Due to hypoalbuminemia resulting in low plasma oncotic pressure, hypovolemia develops that then stimulates the RAAS. More sodium is retained aggravating edema.
Therefore enhanced sodium reabsorption as feature of nephrotic kidney due to intrarenal mechanisms.
Signs and Symptoms of nephrotic syndrome
Edema in the common presentation. But may present with the following complication . Look for them !!!!!
- Protein depletion
- Acute renal failure
- Acute glomerulonephritis
- Acute renal failure
- Chronic renal failure
- Allergic reaction
- Congestive cardiac failure
- Liver disease with hypoalbunimea
- Protein-losing enteropathy
- Urinalysis will indicate hematuria and proteinuria
- Complement C3 levels.
Diagnostic studies for nephrotic syndrome may include the following:
- Urine sediment examination
- Urinary protein measurement.
- Quantification of proteinuria
- 24 hr urine collection
- Timed overnight urine collection
- spot urine
Serum albumin is reduced markedly.
Urea, electrolytes and creatinine levels. sodium levels are low due to dilutional plus very high levels of lipids.
Pcr is raised at presentation.
Serologic studies for infection and immune abnormalities ie Heb B and C
Normal protein diet as per nutritional status of the patient.
High protein diet ↑ protein synthesis but ↑ albumin excretion rather than plasma albumin
Low salt diet. Use of salt during the preparation of food should be avoided in patients with edema. During remission, the child can take food with added salt
If obese due to steroids control calorie intake.
Management of Oedema
Loss of proteinuria produced by prednisolone and the subsequent diuresis usually occurs 7-14 days after initiating treatment in normal saline. There is need to manage edema before this period:
salt restriction- avoid using cooking salt in the food.
Furosemide (1-2mg/kg/day as BD dose) & spironolactone (2mg/kg/day in two divided doses) (spironolactone prevents hypokalemia. Should be started as soon as furosemide is commenced provided the patient not in renal failure.
Diuretics should not be given to a patient with hypovolemia)
No therapeutic tapping for ascites
Corticosteroids ie (prednisone), immunomodulators (cyclophosphamide), and cyclosporine are used to induce remission in nephrotic syndrome.
Angiotensin-converting enzyme inhibitors Captopril, Enalapril and Lisinopril plus Angiotensin II receptor blockers ie Losartan and Valsartan can reduce proteinuria
short-time treatment with Nifedipine or hydralazine. To either may add atenolol
Prevent thrombosis by mobilizing the patient.
These patients require psychological support
Give prophylactic a/b Pen V in patients with gross ascites, Septicemia or peritonitis
1st generation cephalosporins or cloxacillin or flucloxacillin
PLUS 3rd generation cephalosporins
In Hypovolemia, Albumin Infusion is indicated if hypovolemia is characterized by:
- Low BP
- Evidence of renal insufficiency
- Low urinary sodium 1-2mmol/l
Give Albumin 1g/kg/day(OD or BD) over 4 hrs, give furosemide (1-2mg/kg ) 2 hrs after infusion.
Guideline for Steroid Treatment for the First Nephrotic Illness
Prednisolone 60mg/m2/day or 2mg/kg/day max 80mg/day for 4 WEEKS