It refers to what part of the nerve is affected. Differentiation is done with a nerve density skin biopsy and comparing the proximal and distal nerve densities. If the distal nerve densities are decreased and the proximal ones are normal, then it is length dependent. If both are decreased, then it is non-length dependent. Symptoms can vary and should not be the basis of the differentiation. I have symptoms in my feet and hands, but I have a NLDPN. NLDPN and LDPN classically have different causes but there are overlaps, as well as the always fun idiopathic etiology.