If there is fluid in the abdomen, analysis of the fluid could give a good indication for why it is there. Blood values may change rapidly, especially if hemangiosarcoma is present, so repeated lab work may also be helpful. In some case, more sophisticated imaging techniques, such as MRI or CT scans may be necessary to find spinal or brain problems. I am hoping that things have improved, rather than getting worse. Please keep working with your vet to try to find the cause of your rottie's problems so that they may be treated most effectively.
Corticosteroids occur naturally in both dogs and cats.
They are produced by the adrenal gland. They have effects on most of the body's systems. For this reason, using them therapeutically tends to produce a lot of side effects. The most common side effects associated with the use of corticosteroids are increased drinking, urinating and appetite. These effects are less noticeable in cats than dogs but weight gain does seem to accompany the use of corticosteorids in cats pretty frequently.