Hi! Thought I would share some of what I've been through with the endoscopy/GI stuff with my dad. He, too, had some difficulty swallowing and had numerous opinions and scans and always got that "blank stare". Even from specialists. After 6 months of growing difficulty swallowing and constant throwing up, another endoscopy was done and the doc finally ran into a blockage. Here's where the story takes a difficult turn...
During the 6 month stint with all the issues, he had numerous scans that all came back clean. It was apparent the docs were looking for a significant tumor or blockage in the esophogas or small intestine. Although these scans were all fine and he was still considered in remission, there were tiny cancers growing all over his abdominal wall too small for the scan to indicate.
So, when the GI docs came across this blockage, they could not biopsy as it was growing on the OUTSIDE of the esophogas. It was literally blocking the passage for food and all liquids (saliva, etc.) were building up and every hour he would have to spit up. Forceably. He opted for an exploratory surgery to see if teh mass could be removed but, as the surgeon suspected, the cancer was back and he could not even get to the mass causing the problem and recovery from any more surgery would likely have killed him.
SO... stay faithful and expend ALL resources possible to find the problem as early on as you can. Be very persistant and if all else fails, consider an operation to find the problem. This seems to be a pretty common issue with no explanations. And I can promise you do not want your mom to live with such restrictions. Although my dad's cancer is back, it is the dehydration that is causing him to have no quality of life and I think it couls have been avoided to this extent, had we pushed for an operation eralier on. Just something to consider.
Good luck