I have this same thing. And I've been in diagnostic testing since 2018. Mid 2019 showed the elevated levels. And then muscle biopsy done early 2020 showed nothing as expected. I was referred to another neurology clinic for a 2nd opinion. Which I've seen them since early March this year and they are admitting into the hospital for a 5 day stay to receive ivig therapy to help with my symptoms. And I'm so nervous. As you said, there's not much known yet about this. And for me in particular. They've already long ruled out just about every single other diagnosis it could be/that causes sfn. I hope theres more to read in these comments! And I'll share my experience as i go through it!