Does anyone know if demyelination happens and then a person develops the neuropathy?

I ask because the first dr/nerve study showed demyelination she wrote “presumably” from diabetes.

The second doctor (I changed hospital affiliations) nerve study on one arm (cubital to something don’t recall) showed neuropathy but no large fiber neuropathy in legs. Not sure what the difference is between small and large fiber neuropathy is. I thought symptoms were the same.

She did say, to dx the sfn, id need a biopsy. I will see if she would do it.