pitting edema

[audereestfacere]

What exactly causes the pitting in pitting edema vs. non-pitting edema? I understand that one is linked with lymphedema and the other with CHF/cirrhosis/nephrotic.

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[Fuzuli]

Think of the difference between exudate and transudate. If the protein content of the subcutaneous fluid is low, pressing on the edematous area will cause a depression ('pitting'). Vice versa, edema in diseases like acute glomerulonephritis will be hard ('non-pitting').

This is evident in location of edema as well. Pitting edema is evident in lower extremities, especially ankles. On the other hand, edema of eyelids is seen in glomerulonephritis.

Maybe one point to make here is about thyroid diseases. In hypothyroidism and Graves' disease, connective tissue elements (esp. GAG) are deposited in subQ tissue, resulting in myxedema - which is a non-pitting edema (again, this is due to the nature of the deposit).

 

[audereestfacere]

So an exudate is more viscous than a transudate right? I would expect the more viscous fluid to result in pitting. Why isn't this so.

 

[sarcoid]

So an exudate is more viscous than a transudate right? I would expect the more viscous fluid to result in pitting. Why isn't this so.

I think of it like a water balloon (transudate) vs a sand-packed balloon (exudate). Transudate is pure liquid ecf and will allow your finger to push in more easily to cause a dimple/pit (water balloon), while exudate is proteinaceous and has more bulk in the ecf which resists your finger pushing into it (sand-balloon).

It's simple but that's how I think. Hope it helps.