Natural history of cutaneous innervation following herpes zoster

As part of a comprehensive study of the natural history of herpes zoster (HZ), 57 of 94 subjects in a cohort at elevated risk for post-herpetic neuralgia (PHN) consented to collection of 3-mm skin punch biopsies from affected, mirror-image, and distant control skin at baseline and followup visits. As cutaneous innervation is reduced in longstanding severe PHN, we tested the hypothesis that development of PHN is correlated with severity of initial neural injury and/or a failure of neural recovery. Quantitative analysis using single-label PGP9.5 immunofluorescence microscopy showed epidermal profiles were reduced in zoster skin by approximately 40% at study entry compared to control and mirror skin. The density of the subepidermal plexus was approximately 15% lower in zoster skin. Mirror skin was not denervated compared to control skin. Although not significant at all visits, correlations between epidermal nerve fiber density in HZ skin and thermal sensation, allodynia, capsaicin response, and average daily pain all associated more severe abnormalities with lower epidermal innervation. There was limited evidence that the initial neural injury was more severe in the 15 eventual PHN subjects. Overall, pain and pain-related disability resolved the fastest. Sensory abnormalities and symptom aggravation by focal capsaicin application showed partial and selective recovery over 6months. In contrast, cutaneous innervation showed no recovery at all by 6months, conclusive evidence that resolution of pain and allodynia does not require cutaneous reinnervation. A much longer period of observation is needed to determine if zoster-affected skin is ever reinnervated.