Afferent large fiber polyneuropathy predicts the development of postherpetic neuralgia

Abstract

Acute zoster infection may be followed by a chronic pain syndrome, i.e., postherpetic neuralgia (PHN). Besides older age, the intensity of pain and neuronal damage within the acutely affected body region are regarded as predictors or risk factors for PHN. As an alternative approach an underlying peripheral polyneuropathy may be considered as potential co-factor. Is a preexisting generalized impairment of certain fiber classes important in initiating chronic pain states after subsequent localized nerve lesion due to zoster infection? Neurophysiological tests of different efferent and afferent small and large fiber systems were performed prospectively at unaffected body regions in patients with acute herpes zoster. Patients that were still in pain 6 months later (PHN, n=17) and pain free patients (non-PHN, n=17) were compared regarding the results obtained during the acute phase. Both groups were age matched. Nociceptive C-fiber function was assessed at the forearm by quantitative measurement of the axon reflex vasodilatation and flare induced by histamine iontophoresis. Mechanosensitive A β-fibers were tested at all extremities by quantitative vibrametry. Parasympathetic small fiber function was studied by heart rate variability tests. No clinically manifest polyneuropathy was present. However, in PHN risk patients considerably higher vibration detection thresholds in hands and feet were detected compared with non-PHN patients. Pathologic test results of vibration sense at the lower extremity predicted PHN with a sensitivity of 70%. Nociceptive C-fiber and parasympathetic fiber function demonstrated no significant differences in both groups. Acute zoster pain was slightly more intense in the PHN group. We concluded that (i) a mild generalized impairment of afferent A β-fiber function (A β-polyneuropathy) seems to be an important co-factor in the development of PHN and (ii) impairment of vibration sense, i.e., impairment of afferent A β-fiber function, may be used as a predictor of PHN.