Density of sympathetic axons in sural nerve biopsies of neuropathy patients is related to painfulness

In this study, differences of unmyelinated nerve fiber density in sural ner ve biopsy material from patients suffering from neuropathies of unknown ori gin with (n = 14) or without pain (n = 13) were analyzed. Immunocytochemist ry was applied to differentiate afferent sensory and efferent sympathetic n erve fibers. All patients were evaluated for deficits of small fiber functi on with thermotesting, quantitative sudomotor-axon reflex-testing and testi ng of painfulness of mechanical stimuli before performing the biopsy. No di fference was found between patients with and without pain concerning clinic al deficits or results in any of the neurophysiological examinations. There were also no histopathological differences concerning the density of affer ent C-fibers. However, absolute and relative density of efferent sympatheti c nerve fibers was significantly higher in patients with painful neuropathy (P < 0.001), although none of the patients demonstrated clinical sympathet ic abnormalities. We conclude that an imbalance between afferent and sympat hetic nerve tiber density in the periphery may contribute to neuropathic pa in even in those patients without obvious clinical autonomic disturbances. (C) 2000 International Association for the Study of Pain. Published by Else vier Science B.V.