Well this is when it gets crazy. My Neuro told me disease can happen else where and create toxins for nerves. Like celiac! Even people with thyroid have these symptoms. So he told me you start investigating other possibilities but it gets crazy.

You are checking Paraneoplastic.

Like for me nephrologist is next as in need to investigate chronic blood in urine without infections.

But, it still can be deficiencies or reaction to some meds.
I know your thought process right now. We are in the same place with this. Going thru things it can be. And it's frustrating. But I am happy there is no real damage. As biopsy and Emg are normal.

Take care