Is a Skin Biopsy the sensitivest way to know if one suffer from Small fibers Neuropathic Pain?

Can one assume from a normal skin biopsy that he doesn't have Small fibers Neuropathic Pain?

By the way, why is it only performed on the leg? Does anyone knows?

Thank you,

PS: my skin biopsy is only sheduled for June. It is not easly available here in Portugal.