Why doesn't lymphedema pit?

Different location : It has different effect on tissue than edema from other blood vessels so that there is swelling without pitting.

Nowhere to shift H2O: Lymphedema occurs when the lymphatic load exceeds the transport capacity of the lymphatic system, which causes filtered fluid to accumulate in the interstitium. As opposed to generalized edematous states, the rate of capillary filtration is normal in patients with lymphedema. Pitting reflects movement of the excess interstitial water in response to pressure. Hi tissue pressure prevents shift.

It can: Early lymphedema can pit, which is one of the reasons why it can be hard to diagnose in its early stages. This is especially true if there is also some component of venous insufficiency associated with the lymphedema. Later stages of lymphedema are associated with tissue fibrosis which has lost its ability to be able to pit.