Nephrotic syndrome is urinary excretion of 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary causes. Diagnosis is by determination of urine protein/creatinine ratio in a random urine sample or measurement of urinary protein in a 24-hour urine collection; cause is diagnosed based on history, physical examination, serologic testing, and renal biopsy. Prognosis and treatment vary by cause.
(See also Overview of Glomerular Disorders.)
Etiology of Nephrotic Syndrome
Nephrotic syndrome occurs at any age but is more prevalent in children (primarily minimal change disease), mostly between ages 1½ and 4 years. Congenital nephrotic syndromes appear during the first year of life. At younger ages (< 8 years), boys are affected more often than girls, but both are affected equally at older ages. Causes differ by age (see table Glomerular Disorders by Age and Presentation) and may be primary or secondary (see table Causes of Nephrotic Syndrome).
The most common primary causes are the following:
Secondary causes account for < 10% of childhood cases, but > 50% of adult cases, most commonly the following:
Amyloidosis, an underrecognized cause, is responsible for 4% of cases.
HIV-associated nephropathy is a type of focal segmental glomerulosclerosis that occurs in patients with AIDS.
Pathophysiology of Nephrotic Syndrome
Proteinuria occurs because of changes to capillary endothelial cells, the glomerular basement membrane (GBM), or podocytes, which normally filter serum protein selectively by size and charge.
The mechanism of damage to these structures is unknown in primary and secondary glomerular diseases, but evidence suggests that T cells may upregulate a circulating permeability factor or downregulate an inhibitor of permeability factor in response to unidentified immunogens and cytokines. Other possible factors include hereditary defects in proteins that are integral to the slit diaphragms of the glomeruli, activation of complement leading to damage of the glomerular epithelial cells and loss of the negatively charged groups attached to proteins of the GBM and glomerular epithelial cells.
Complications of nephrotic syndrome
erythropoietinComplications of Nephrotic Syndrome); other physiologic factors also play a role.
Symptoms and Signs of Nephrotic Syndrome
Primary symptoms include anorexia, malaise, and frothy urine (caused by high concentrations of protein).
Fluid retention may cause
Dyspnea (pleural effusion or laryngeal edema)
Arthralgia (hydrarthrosis)
Abdominal pain (ascites or, in children, mesenteric edema)
Corresponding signs may develop, including peripheral edema and ascites. Edema may obscure signs of muscle wasting and cause parallel white lines in fingernail beds (Muehrcke lines).
Other symptoms and signs are attributable to the many complications of nephrotic syndrome (see table Complications of Nephrotic Syndrome).
Diagnosis of Nephrotic Syndrome
Urine random (spot) protein/creatinine ratio ≥ 3 or proteinuria ≥ 3 g/24 hours
Serologic testing and renal biopsy unless the cause is clinically obvious
Diagnosis is suspected in patients with edema and proteinuria on urinalysis and confirmed by random (spot) urine protein and creatinine levels or 24-hour measurement of urinary protein. The cause may be suggested by clinical findings (eg, systemic lupus erythematosus, preeclampsia, cancer); when the cause is unclear, additional (eg, serologic) testing and renal biopsy are indicated.
Urine testing
A finding of significant proteinuria (3 g protein in a 24-hour urine collection) is diagnostic (normal excretion is < 150 mg/day). Alternatively, the protein/creatinine ratio in a random urine specimen usually reliably estimates grams of protein/1.73 m2 body surface area (BSA) in a 24-hour collection (eg, values of 40 mg/dL protein and 10 mg/dL [884 micromol/L] creatinine in a random urine sample are equivalent to the finding of 4 g/1.73 m2 in a 24-hour specimen).
Calculations based on random specimens may be less reliable when creatinine excretion is high (eg, during athletic training) or low (eg, in cachexia). However, calculations based on random specimens are usually preferred to 24-hour collection because random collection is more convenient and less prone to error (eg, due to lack of adherence); more convenient testing facilitates monitoring changes that occur during treatment.
Besides proteinuria, urinalysis may demonstrate casts (hyaline, granular, fatty, waxy, or epithelial cell). Lipiduria, the presence of free lipid or lipid within tubular cells (oval fat bodies), within casts (fatty casts), or as free globules, suggests a glomerular disorder causing nephrotic syndrome. Urinary cholesterol can be detected with plain microscopy and demonstrates a Maltese cross pattern under crossed polarized light; Sudan staining must be used to show triglycerides.
Adjunctive testing in nephrotic syndrome
Adjunctive testing helps characterize severity and complications.
< 2.5 g/dL (25 g/L).
Total cholesterol and triglyceride levels are typically increased.
It is not routinely necessary to measure levels of alpha- and gamma-globulins, immunoglobulins, hormone-binding proteins, ceruloplasmin, transferrin, and complement components, but these levels may also be low.
Testing for secondary causes of nephrotic syndrome
The role of testing for secondary causes of nephrotic syndrome (see table Causes of Nephrotic Syndrome) is controversial because yield may be low. Tests are best done as indicated by clinical context. Tests may include the following:
Serum glucose or glycosylated Hb (HbA1C)
Antinuclear antibodies
Serum and urine protein electrophoresis
Cryoglobulins
Rheumatoid factor
Serologic test for syphilis (eg, rapid plasma reagin)
Complement levels (C3, C4)
Test results may alter management and preclude the need for biopsy. For example, demonstration of cryoglobulins suggests mixed cryoglobulinemia (eg, from chronic inflammatory disorders such as systemic lupus erythematosus, Sjögren syndrome, or hepatitis C virus infection), and demonstration of a monoclonal protein on serum or urine protein electrophoresis suggests a monoclonal gammopathy (eg, multiple myeloma), especially in patients > 50 years who have anemia.
Renal biopsy is indicated in adults to diagnose the disorder causing idiopathic nephrotic syndrome. Idiopathic nephrotic syndrome in children is most likely minimal change disease and is usually presumed without biopsy unless the patient fails to improve during a trial of corticosteroids. Specific biopsy findings are discussed under the individual disorders.
Treatment of Nephrotic Syndrome
Treatment of causative disorder
Angiotensin inhibition
Sodium restriction
Statins
Diuretics for excessive fluid overload
Rarely, nephrectomy
Treatment of disorder causing nephrotic syndrome
Proteinuria treatment
hyperkalemia in patients with moderate to severe renal insufficiency.
Protein restriction is not recommended because of lack of demonstrated effect on progression.
Edema treatment
Sodium restriction (< 2 g sodium, or about 100 mmol/day) is recommended for patients with symptomatic edema.
Dyslipidemia treatment
Statins are indicated for dyslipidemia.
Limitation of saturated fat and cholesterol intake is recommended to help control dyslipidemia.
Hypercoagulability treatment
Anticoagulants are indicated for treatment of thromboembolism, but few data exist to support their use as primary prevention.
Management of infection risk
All patients should receive pneumococcal vaccination if not otherwise contraindicated.
Nephrectomy for nephrotic syndrome
Rarely, bilateral nephrectomy is necessary in severe nephrotic syndrome because of persistent hypoalbuminemia. The same result can sometimes be achieved by embolizing the renal arteries with coils, thus avoiding surgery in high-risk patients. Dialysis is used as necessary.
Prognosis for Nephrotic Syndrome
Prognosis varies by cause. Complete remissions may occur spontaneously or with treatment. The prognosis generally is favorable in corticosteroid-responsive disorders.
In all cases, prognosis may be worse in the presence of the following:
Infection
Hypertension
Significant azotemia
Hematuria
Thromboses in cerebral, pulmonary, peripheral, or renal veins
The recurrence rate is high in kidney transplantation patients with focal segmental glomerulosclerosis, immunoglobulin A (IgA) nephropathy, or membranoproliferative glomerulonephritis (especially type 2).
Key Points
Nephrotic syndrome is most common in young children, is usually idiopathic, and is most often minimal change disease.
In adults, nephrotic syndrome is usually secondary, most often to diabetes or preeclampsia.
Consider nephrotic syndrome in patients, particularly young children, with unexplained edema or ascites.
Confirm nephrotic syndrome by finding spot protein/creatinine ratio ≥ 3 or urinary protein ≥ 3 g/24 hours.
Do tests for secondary causes and renal biopsy selectively, based on clinical findings.
Assume minimal change disease if a child with idiopathic nephrotic syndrome improves after treatment with corticosteroids.
Treat the causative disorder with disease-specific therapy.
Administer angiotensin inhibition, sodium restriction, and often diuretics and/or statins to manage proteinuria, edema, and hyperlipidemia.
