My dog's decreased mobility on one side

My dog (pekingese) has had two spinal surgeries due to ruptured discs (c 4, 5) and now shows decreased mobility on his right side. The neurosurgeon who did the surgeries before said that my dog has a "cyst" around the injured nerve and there is nothing he can do about it. He then said that my dog's symptoms could be from hyperfunction of its adrenal. Then he ordered ACTH stimulation test. But his resident called back with the result of being "insignificant" then recommended abd ultrasound. Here is the interest part: his resident said that my dog's cortisol level pre-ACTH injection was lower than normal but it went too high post ACTH injection. So she thinks that my dog still has cushing's and she would like to see if my dog has a tumor in its adrenal by using abd ultrasound. My questions are:
1. Clinical manifestations of Cushing's include decreased mobility? I thought hypofunction of adrenals may cause sluggishness ...
2. Wouldn't it be hypofunction if serum cortisols is low to begin with? Then after ACTH and cortisols increasing showing possible secondary adrenal insufficiency (problem at the pituitary)?
3. My dog is doing better with Metacam. Should I continue using it?

Please help me ...