Post-herpetic neuralgia (PHN) is a common complication after herpes zoster (HZ). The severity of neuronal injury may predict development of PHN. The changes in cutaneous innervation following HZ are poorly understood. There are signs of denervation in the painful skin in most, but not all, patients with PHN. Previous studies have focused on quantification of the cutaneous innervation. In a large piece of skin from a patient with chronic severe PHN we demonstrated a distinctly abnormal pattern of cutaneous nerve morphology and immunohistochemistry which were much more complex than what had been suggested by assessment of fiber density. The aim of this study was to assess if abnormal patterns of cutaneous nerve immunohistochemistry were associated with severe PHN. We compared immunochemical characteristics of cutaneous innervation in skin biopsies collected in two groups: 1. Twelve patients without pain 40 months (range 23-50 months) after HZ onset and 2. Twelve patients with chronic severe PHN (mean pain rating 65 on the 0-100 pain VAS [range 40 - 80]) 40 months after HZ onset (range 8-73 months) (1). Using double labeling immunohistochemistry we stained the biopsies using PGP 9.5, CGRP, and NF. The biopsies were analyzed blindly, in random and by one observer. Outcome measures included: density of CGRP positive (CGRP+/PGP+) fibers as a measure of peptidergic fibers; density of CGRP negative (CGRP-/PGP+) fibers as a measure of non-peptidergic fibers and density of NF-positive (NF+/PGP+) fibers as a measure for the density of myelinated fibers in the epidermis, subepidermis and dermis. Preliminary analysis suggests that there is an abnormal expression of CGRP and NF in the PHN skin compared to mirror-image skin. Immunochemical analyses are in progress.

1. Petersen KL et al. Capsaicin evoked pain and allodynia in post-herpetic neuralgia. Pain 2000