Characterization of neural content of dermal nerve bundles (DNBs), and correlation with a range of epidermal nerve fiber density (ENFD)

Skin biopsy for measurement of ENFD is a commonly used and proven clinical method for diagnosis of peripheral neuropathy and quantification of severity. Methods for quantification of cutaneous autonomic innervation have been described in sweat glands, arrector pili and blood vessels, but are limited by the dense and chaotic architecture of nerves in these target structures. Large dermal nerve bundles consist largely of c-fibers, and while offering more compact, well-organized architecture for morphometry, formal descriptions have been limited. 

50 skin biopsies from foot dorsa were performed in patients describing neuropathic pain or paresthesias, and ENFD was measured. For each biopsy, the largest DNB seen was imaged and analyzed on a section triple-stained with PGP 9.5, VIP and CollIV using a confocal microscope. Image stacks are taken at 60x with 0.5um z-sections so that all fibers in the bundle are included. VIP+ and PGP9.5+ fibers are counted by the authors, who were blinded to ENFD. DNB diameter and the shortest straight-line distance from the epidermis are measured, and DNB fiber density (fibers/DNB area) and autonomic fiber percent are calculated. 

27-101 PGP9.5+ fibers and 0-7 VIP+ fibers were seen per DNB. DNB fiber density correlates positively with ENFD. Numerous dermal nerve fibers remained within bundles, even in biopsies with markedly reduced ENFD. ENFD correlated directly with DNB diameter and inversely with autonomic fiber percent.