This is a renal disorder that is characterized by proteinuria greater than 3. 5 grams per day, peripheral edema, hypoalbuminemia and hyperlipidemia. Proteinuria is the hallmark of the disease, and many cases initially present as persistent proteinuria on urinalysis prompting the physician to pursue this diagnosis. Hypoalbuminemia results from the aforementioned urinary protein loss, increased renal catabolism and inadequate hepatic synthesis. Hypoalbuminemia results in a lowered plasma oncotic pressure, which can not compete with the normal hydrostatic pressure mediated migration of intravascular fluid into peripheral tissues. The dysequilibrium of plasma hydrostatic and oncotic pressures results in the formation of peripheral edema. Hyperlipidemia results from hepatic lipoprotein synthesis. Elevation of low density lipoproteins and cholesterol are the lipid abnormalities most commonly associated with nephrotic syndrome.
Patients with nephrotic syndrome (especially when proteinuria is greater than 10 grams/day and hypoalbuminemia is less than 2.0 grams/dL) are at increased risk of thromboembolic complications secondary to low levels of serum antithrombin III, protein C and protein S. These serum anticoagulants are lost in the urine with other serum proteins. Physicians should be alert to the possibility of thrombosis (particularly renal vein thrombosis) with resultant pulmonary emboli.
Nephrotic syndrome may be either primary or the result of some underlying disease process. An aggressive search for secondary causes should be attempted before subjecting the patient to renal biopsy. Common secondary causes include diabetes mellitus, hepatitis B and C, syphilis, systemic lupus erythematosus, multiple myeloma and medications.
Therapy for nephrotic syndrome is to determine the etiology and treat if possible (minimal change disease, also termed Nil disease, is often responsive to prednisone 1-1. 5 mg/kg PO QD for four weeks followed by prednisone 1 mg/kg PO QOD for four weeks) although the renal damage may persist. Edema is treated with diuresis using loop diuretics. Caution should be exercised not to be overly aggressive with diuresis as a decrease in the effective intravascular volume may result The resultant dehydration would manifest as a reduction in the glomerular filtration rate (GFR), azotemia and orthostatic hypotension. The azotemia would be secondary to prerenal acute renal failure and may progress to acute tubular necrosis if not corrected. Hyperlipidemia may be treated with antilipid agents; however, it is controversial whether the hyperlipidemia associated with nephrotic syndrome is atherogenic and, if not, whether therapy is warranted. Once patients manifest signs of hypercoaguability, they should be placed on long term anticoagulation therapy with warfarin.