Chapter 53 Nephrotic Syndrome
PATHOPHYSIOLOGY
Nephrotic syndrome is the clinical state in which the glomerular membrane has an increased permeability to plasma proteins. This leads to severe edema, proteinuria, and hypoalbuminemia. The loss of protein from the vascular space causes decreased plasma osmotic pressure and increased hydrostatic pressure, resulting in the accumulation of fluids in interstitial spaces and the abdominal cavity. The decrease in vascular fluid volume stimulates the renin-angiotensin system, resulting in secretion of antidiuretic hormone (ADH) and aldosterone. Tubular resorption of sodium (Na+) and water is increased, expanding the intravascular volume. This fluid retention leads to increased edema as retained fluid shifts into the interstitial space. Coagulation and venous thrombosis may occur as a result of decreased vascular volume, which causes hemoconcentration and urinary loss of coagulation proteins. Loss of immunoglobulins through the glomerular membrane can lead to increased susceptibility to infection. Hyperlipidemia is believed to occur because of increased synthesis of lipoproteins in response to low plasma oncotic pressure.
Nephrotic syndrome is the pathologic outcome of various factors that alter glomerular permeability. The causes of nephrotic syndrome can be categorized into primary (idiopathic) and secondary (Box 53-1). Primary nephrotic syndrome is divided into three histologic groups: minimal-change nephrotic syndrome (MCNS), focal segmental glomerulosclerosis (FSGS), and membranous neuropathy (rare in children). Based on clinical classification, the syndrome types differ according to the course of the disease, treatment, and prognosis. It is considered a chronic illness because of the occurrence of relapses. Many children will have five or more relapses over the course of the disease. A child is considered to have frequently relapsing nephrotic syndrome if there are two or more relapses within the first 6 months and/or four or more relapses within a 12-month period. The frequency of relapse decreases over time and becomes relatively rare by adolescence.
Box 53-1 Causes of Nephrotic Syndrome
Primary
INCIDENCE
1. The prevalence of idiopathic nephrotic syndrome is approximately 16 per 100,000.
2. Idiopathic nephrotic syndrome can occur at any age. Most often, it first manifests in children between ages 2 and 6 years.
3. Of all cases of nephrotic syndrome in children, 80% are MCNS. Incidence is slightly greater in males.
4. The mortality and prognosis of children with nephrotic syndrome vary with the disorder’s etiology and severity, the extent of renal damage, the child’s age and underlying condition, and response to treatment.
5. Nephrotic syndrome mortality and prognosis can range from complete recovery to causing end-stage renal disease (ESRD).
6. Children with MCNS tend to have a good prognosis.
7. Prognosis is more likely to be poor in children who do not respond to treatment and/or with some of the less common types of nephrotic syndrome such as FSGS.
CLINICAL MANIFESTATIONS
Although the child’s symptoms will vary with different disease processes, the most common symptoms associated with nephrotic syndrome are the following:
1. Decreased urine output with dark, frothy urine
COMPLICATIONS
1. Fluid/electrolyte balance: intravascular volume depletion (hypovolemia), respiratory compromise (related to fluid retention and abdominal distention), skin breakdown (from severe edema, poor healing)
2. Cardiovascular: hypercoagulability (venous thrombosis)
3. Immune: infection (especially cellulitis, peritonitis, pneumonia, septicemia)
4. Multiple body systems: untoward side effects of medications, growth failure, and muscle wasting (long-term)
LABORATORY AND DIAGNOSTIC TESTS
Nephrotic syndrome is generally diagnosed based on clinical presentation and laboratory test results.
Refer to Appendix D for laboratory and diagnostic values.
1. Urinalysis, urine dipstick—to detect protein and blood in the urine.
2. Urinary protein/creatinine ratio—calculated to monitor persistent proteinuria; best if first void of the morning is used; more accurate than 24-hour urine protein collection
3. Serum chemistry, lipid panel—to assess electrolytes, serum protein, renal function, lipids
4. Complete blood count—to monitor for hemoconcentration and infection
