A few years ago, our lurcher Buddy, became swollen. She didn't get a massive amount of swelling around her abdomen (although she did get some) but she got it mainly around her face and on her legs. They were literally just like bags of fluid.
This is what Buddy look like under normal circumstances
But this is what she looked like when she was swollen
She was losing protein and through a process of elimination, it was determined that it was from her gut. The vets were very reluctant to perform a gut biopsy because it was explained to me that if it is indeed PLE, the gut would take an awful long time to heal and this could cause even more problems than we had at the present time.
Buddy was treated with steriods and a change of diet (low fat, high protein) and she also had the white of one egg per day to increase her albumin levels. Over a period of time she was retested and then after more time (maybe about 6 months in total) she was weaned off all medication and she went back to her normal diet.
I'm not sure if this helps you in any way but I thought it might be worth sharing, just in case.
Sending best wishes for your dog