Amplitudes of Pain-Related Evoked Potentials Are Useful to Detect Small Fiber Involvement in Painful Mixed Fiber Neuropathies in Addition to Quantitative Sensory Testing - An Electrophysiological Study.

Niels Hansen,Daniel Zeller,Nurcan Üçeyler,Claudia Sommer,Ann-Kathrin Kahn,Zaza Katsarava

doi:10.3389/fneur.2015.00244

Abstract

To investigate the usefulness of pain-related evoked potentials (PREP) elicited by electrical stimulation for the identification of small fiber involvement in patients with mixed fiber neuropathy (MFN). Eleven MFN patients with clinical signs of large fiber impairment and neuropathic pain and ten healthy controls underwent clinical and electrophysiological evaluation. Small fiber function, electrical conductivity and morphology were examined by quantitative sensory testing (QST), PREP, and skin punch biopsy. MFN was diagnosed following clinical and electrophysiological examination (chronic inflammatory demyelinating neuropathy: n = 6; vasculitic neuropathy: n = 3; chronic axonal neuropathy: n = 2). The majority of patients with MFN characterized their pain by descriptors that mainly represent C-fiber-mediated pain. In QST, patients displayed elevated cold, warm, mechanical, and vibration detection thresholds and cold pain thresholds indicative of MFN. PREP amplitudes in patients correlated with cold (p < 0.05) and warm detection thresholds (p < 0.05). Burning pain and the presence of par-/dysesthesias correlated negatively with PREP amplitudes (p < 0.05). PREP amplitudes correlating with cold and warm detection thresholds, burning pain, and par-/dysesthesias support employing PREP amplitudes as an additional tool in conjunction with QST for detecting small fiber impairment in patients with MFN.

Highlights

Painful polyneuropathies of different origin often affect large- and small-nerve fibers [1, 2] and are termed mixed fiber neuropathies (MFN)
Eleven patients with neuropathic pain and signs of large-fiber involvement were classified as patients with painful mixed fiber neuropathy (MFN)
The patient group consisted of six patients with chronic inflammatory demyelinating neuropathy (CIDP) [26], three patients with vasculitic neuropathy [27], and two patients with chronic axonal neuropathies

Summary

Introduction

Painful polyneuropathies of different origin often affect large- and small-nerve fibers [1, 2] and are termed mixed fiber neuropathies (MFN). Small thinly myelinated as well as unmyelinated nerve fibers (Aδ- and C-fibers) can be assessed via neurological examination and quantitative sensory testing (QST) [6]. Both methods are subjective and very dependent on patients’ cooperation. Inclusion criteria consist of female and male patients at the age of ≥18 years, confirmed diagnosis of painful motor or sensory polyneuropathy (by medical report, neurological examination, standard neurophysiology). A robust and reproducible PREP response was a prerequisite for including MFN patients in our study, as we were dedicated to delineating the differences between PREP latencies and amplitudes in patients and controls

Results

Discussion

Conclusion