Bilateral hind leg pitting edema with no identifiable underlying cause?

Hello, I am turning to the internet because I am running out of ideas. Hoping someone may have some experience with this, and can maybe help.

Short version: Has anyone ever had a dog who had pitting edema of the hind legs with no real medical cause? How did it go?



TL;DR Version: I have a 6 year old Mastiff, named Kingston. Last year, his hind legs swelled up with pitting edema. It was so bad that he could not bend his legs to lay down.

I assumed he was in CHF because unfortunately, he has lost quite a few siblings to heart failure already.

We did x-rays, an ultrasound, and aspirated lymph nodes, and most of it pointed to lymphoma. Heart sounded/looked good. We opted not to do chemo, because to find out what type of chemo to do, we would have had to send the aspirated fluid to colorado. This would mean any treatment (and comfort) would have to wait until the results were back. This dog was not going to be able to wait for comfort.

We started prednisone, and the swelling went down. But everything else went downhill too. He started losing weight rapidly, had massive muscle wasting, became completely incontinent and basically looked and acted like he was dying of cancer.

Except there was something nagging in me that told me he didn't have cancer. I felt this sick feeling that the prednisone was what was causing him to go downhill fast.

I started weaning him off the pred and even down to half dose, he was still in horrid shape. Eventually, I made an appt for a mobile vet to come and let him go.

The day I made the appt, I didn't give his meds that morning. I let my vet know that I was stopping the prednisone, and he told me not to, so I gave him just one dose that day (because I already skipped his morning dose). The next day he just got one dose again... the third day was euth date. And he was so much better. I canceled his euthanasia and as days passed, I watched my dog come back to life!!

Since then, however, (last july/August) he has had more episodes of swelling, in October, swelling came back with other weird symptoms, vasculitis, hair loss, cracking nose, all these things that pointed to SLE. Tested negative for SLE on a coombs test. SLE symptoms eventually dissipated.

Since then, he has had more flare ups of swelling with no other real symptoms, besides maybe some lethargy (which is hard to determine in an already lazy mastiff)

So, the Coombs test came back negative, as did every tick borne illness panel we've run (and we have run many). We have had some borderline anemia, but it seems to bounce back.

Had some histiocytomas biopsied, nothing malignant...

Pitting edema is back again, seems worse than it's been in a while this time.

Any ideas at all? so sorry for the novel. Thanks in advance

I'm so sorry, I have no experience of this but I hope somebody will come along who can help.