Nephrotic Syndrome

By now you may already know that the kidneys filter your blood. Microscopically speaking, it is structures known as the glomeruli (singular ‘glomerulus’) inside of the kidney that perform the actual filtration. If they, like the car and fridge filter, are damaged, then they will leak stuff into your urine that normally shouldn’t be there.

A glomerular disorder that causes hypoalbuminemia, proteinuria, and edema is known as nephrotic syndrome. All sorts of glomerulopathies (diseases of the glomerulus) can result in nephrotic syndrome, including: 

  • Minimal change disease 
  • Focal segmental glomerulosclerosis 
  • Membranous nephropathy 
  • Diabetic nephropathy 

CAUSES OF NS

Minimal change disease:

  • PRIMARY CAUSE: IDIOPATHIC (10–15% of idiopathic NS in adults, but 70–90% of NS in children.)
  • SECONDARY CAUSE: HIV
  • CAUSED BY DRUGS: NSAIDS, Rifampicin interferon
  • NEOOPLASMIC: Hodgkin’s lymphoma
  • mc in children

Membranous nephropathy 

  • PRIMARY CAUSE: IDIOPATHIC (30% of idiopathic adult NS.)
  • SECONDARY CAUSE: Chronic Hep B/C, Syphillis, Leprosy, Hydatid disease
  • CAUSED BY DRUGS: NSAIDS, Gold, Penicillamine, Probenecid, Captopril
  • NEOOPLASMIC: Paraneoplastic syndrome (IgG) and Ca of breast, lung, ovary and colon.
  • mc in elderly and malignant lesions
  • maximum risk of renal vein thrombosis

Focal segmental glomerulosclerosis 

  • PRIMARY CAUSE: IDIOPATHIC (30% of idiopathic adult NS.)
  • SECONDARY CAUSE: Chronic Hep B, Parvo B-19
  • CAUSED BY DRUGS: NSAIDS, Heroine intake, Lithium and Panidronate
  • NEOOPLASMIC: Non- Hodgkin’s lymphoma
  • mc in adults
  • mc lesion in HIV

I don’t want you to really get bogged down in remembering the causes of nephrotic syndrome so much as understanding what actually happens. Any of those diseases damage the glomerulus. The glomerulus is the filter that is supposed to keep large things, such as proteins, inside of the blood while filtering out smaller toxins that get excreted in the urine. If the pores of the glomerulus, the little holes that allow for things to pass through the glomerulus and into the urine, are damaged, they get bigger. Bigger pores in any filter means that things that should’ve been kept out are now leaking into the urine and out of the blood. 

You can reproduce this point at home. Take out some dirty old rag you no longer need. If you look really closely, you will see that there are small holes in the rag. They’re truly tiny. This rag will represent our glomerulus, the filter. Turn on the faucet in a sink and place a couple of golf balls or something similar into the rag. Now place all of this under the running faucet. You’ll note that the golf balls aren’t filtered through, but the water and all the microscopic parts of it easily pass through to the other side. 

Now go ahead and cut some big holes into the rag, mimicking the damage glomerulopathies cause. Repeat what you did before. This time around, not only will the water leak through but the golf balls will pass through as well. 

In the case of nephrotic syndrome, a protein called albumin is like a golf ball that leaks out of the blood and into urine when it normally shouldn’t. This leakage results in decreased levels of albumin in the blood, termed hypoalbuminemia and increased levels of protein in the urine, known as proteinuria.

SERUM ALBUMIN= Normal Value is 3.5-5.5 but in NS the value decreases to 2.5 g/dl
PROTENURIA
Old= more than 3.5 g/dl
Children= More than 2g/dl
Adult= More than 3g/dl
Proteinuria during nephrotic syndrome is in the range of three grams per day or more. This is in contrast to other causes of proteinuria, such as a kidney infection, which results in less than that (up to two grams per day, normally). 

You should note that the protein albumin, now leaking out of blood and into the urine, is important in keeping fluid within the blood vessels and out of the body tissues. Albumin is like a sponge that sucks up water into the vasculature. Since there’s less albumin in the blood during nephrotic syndrome, there are fewer sponges in the blood vessels. This means water leaks out of the blood vessels and into the tissues. This is what is known as edema. Edema causes a person to literally swell up with fluid. Keeping this in mind, lets understand:
Initiating Mechanism of Edema:
Decrease in oncotic pressure due to albumin loss —> Fluid shift from intravascular to extravascular—> causing effective decrease in intravascular volume.
Hence, increase in renin and aldosterone leading to increase in water and sodium retention.

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