I searched for antiganglioside on Google and got all sorts of stuff. Most of which means nothing in terms of what your doctor is looking for. Have you asked your doc about the tests? That would be the first place I'd start.
I had those tests three years ago and I believe they are to eliminate multifocal motor neuropathy which is similar to ALS but potentially treatable. I also understand that the tests results are not necessarily conclusive, but a positive antibody test will justify attempts to treat your condition with immune modulating treatments such as IVIG.
be careful with bloodwork that is sent out to this lab. no-one told us that the bloodwork was not coverd by our insurance, and athena lab does not negotiate price. to our surprise we were billed several hundred dollars. I guess that is the same as buyer be ware.