I agree with Dash. An abdominal ultrasound would be a good idea. They don't always show up on imaging but there is an adrenal tumor called a pheochromacytoma which can cause all of the symptoms you have described. When you say your dog has seen a specialist, I assume you mean an internal medicine specialist (IMS) as they are the experts when it comes endocrine disorders such as addison's. I would recommend that you discuss the possibility of a pheo with the specialist and definitely ask for an ultrasound. If your dog saw an IMS, I would be surprised that an abdominal ultrasound was not already one of the diagnostics on the menu. Blood pressure should also be checked.
Adrenal Pheochromocytoma