Lungs okay but can't breathe; neuro-muscular issues, no diagnosis

My 78-year-old brother (in rural PA) is having severe breathing issues. I'm not sure about all of his history or symptoms but I'll try. Last fall (9/2021) his doctors changed his thyroid med. and increased his metformin. I don't know what prompted the change. Concurrently his long time GP retired, and the practice suffered. His records became unavailable.

More background info: He is only a light social drinker, has not smoked for over 40 years, and is (was!) physically active (martial arts, hunting, gardening, grandchildrening). His weight was mostly within normal parameters for someone of his height and age. He may have had some exposure to mold in his basement and at the nuclear power plant where he worked as a consultant. He may have had exposure to tick bites. He spent time primarily in Pennsylvania and Maine. He and his wife have been together since their mid-teens and married for 55 years. He had become diabetic and had thyroid issues. He also served in the air force as a young man.

The main issues over the following nine months were weight loss (about 70#), diarrhea, difficulty breathing, and his speech became slurred. This culminated in his losing consciousness twice while driving (no accident occurred). He made it home and his wife immediately took him to the emergency room of their local hospital.

His CO2 level was 90%. Any higher and he would have been dead!
Obviously, he was not only restricted in his oxygen intake, but he was also unable to expel the CO2. They performed many tests which revealed nothing. His lungs were clear. His heart was fine (he had had a heart attack about 20 years ago but nothing beyond that). They found no evidence of cancer. His blood work, once they stopped looking at the labs from September and did new testing, did not reveal any cause for his issues. They suggested that he was in the last stages of ALS. He had never been diagnosed with ALS and the motor function in his arms and legs is normal. He was eventually put in ICU, stabilized and then moved to a larger hospital in Reading, PA.

There he was seen by a neuro-muscular specialist. He was intubated and put on a ventilator. They performed a spinal tap and an EMG. The working diagnosis was Lambert Eaton disease, and he was given a course of five plasmaphereis (blood washing) treatments. He has not progressed as they had hoped. His mental acuity and his limb motility remain intact. The LE has not been confirmed and they don't have another possible diagnosis or treatment plan yet. Today they are performing a tracheotomy to allow the removal of the intubation and hopefully move him closer to a move to rehab facility and eventually home.

Without a diagnosis there doesn't seem to be a way to create a treatment plan that could lead to the removal of the trach. and a return to normalcy.

Does anyone have any experience with anything that matches this uncommon malady?