Jack Is 68 Years Old, With Controlled Diabetes. My Friend,

Jack is 68 years old, with controlled diabetes.
My friend, Jack, was diagnosed with non-Hodgkin's lymphoma about 3 years ago. He went through treatment at Vanderbilt medical center in Nashville. He was in remission for less than a year. At this point, instead of doing the normal second round of treatments, he was placed on a drug called imbruvica. He took this drug for over a year. There are no traces of cancer, but Jack is very sick. He had a thorough check-up in March and he seemed to be weakening...fatigue and loss of stamina...but the doctors recommended that he continue on imbruvica. In April he had a sinus infection, and it's been nothing but downhill since then. His first symptom, other than the fatigue, was dizziness. He says his head just feels "funny." Then the dizziness turned into balance issues. Vomiting was next...sudden, spontaneous vomiting. His weakness and fatigue worsened, he had to start walking with a walker because of frequent falling, and his weight was plummeting. He was taken off the imbruvica and there was no change. Add confusion and night time urination, as many as a dozen times a night, to the myriad of symptoms. At one time, during the summer, he was given a round of steroids and seemed to have some brief improvement. He returned to Vanderbilt about a month ago and, once again, all his tests showed no signs of illness, including an MRI on his head and lots of blood work. I know PML was ruled out as was paraneoplastic syndrome. Between his doctors being on vacation and such, nothing has changed except Jack is still extremely sick and can no longer safely walk by himself and is skeletal. 6'2" and 160. MS and Addison's disease have also been ruled out. He has another appointment at Vanderbilt in about two weeks, but has been told than it will only be a consultation and that no more tests will be run.
Jack is an invalid, very close to needing to be in a nursing home as his wife is not capable of caring for him totally. She is desperate to find a diagnosis and is willing to take him to Mayo, but doesn't know if Jack can make the trip. Please advise.