Differential involvement of A-delta and A-beta fibres in neuropathic pain related to carpal tunnel syndrome

Truini, A.; Padua, L.; Biasiotta, A.; Caliandro, P.; Pazzaglia, C.; Galeotti, F.; Inghilleri, M.; Cruccu, G.

doi:10.1016/j.pain.2009.05.023

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Volume 145, Issue 1 , Pages 105-109, September 2009

Differential involvement of A-delta and A-beta fibres in neuropathic pain related to carpal tunnel syndrome

A. Truini
- Department of Neurological Sciences, University “La Sapienza”, Rome, Italy
- Department of Neurological Sciences, IRCCS San Raffaele Pisana, Rome, Italy
- Corresponding author. Address: Department of Neurological Sciences, University “La Sapienza”, Viale Università 30, 00185 Rome, Italy. Tel.: +39 06 49914196; fax: +39 06 49914525.
L. Padua
- Institute of Neurology, Università Cattolica, Fondazione Don Gnocchi, Rome, Italy
A. Biasiotta
- Department of Neurological Sciences, University “La Sapienza”, Rome, Italy
P. Caliandro
- Institute of Neurology, Università Cattolica, Fondazione Don Gnocchi, Rome, Italy
C. Pazzaglia
- Institute of Neurology, Università Cattolica, Fondazione Don Gnocchi, Rome, Italy
F. Galeotti
- Department of Neurological Sciences, University “La Sapienza”, Rome, Italy
- National Centre for Epidemiology, Surveillance, and Health Promotion, National Institute of Health, Rome, Italy
M. Inghilleri
- Department of Neurological Sciences, University “La Sapienza”, Rome, Italy
- Department of Neurological Sciences, IRCCS San Raffaele Pisana, Rome, Italy
G. Cruccu
- Department of Neurological Sciences, University “La Sapienza”, Rome, Italy
- Department of Neurological Sciences, IRCCS San Raffaele Pisana, Rome, Italy

Received 15 January 2009; received in revised form 21 April 2009; accepted 22 May 2009. published online 17 June 2009.

Abstract

Carpal tunnel syndrome (CTS), a common entrapment neuropathy involving the median nerve at the wrist, frequently manifests with neuropathic pain. We sought information on pain mechanisms in CTS.

We studied 70 patients with a diagnosis of CTS (117 CTS hands). We used the DN4 questionnaire to select patients with neuropathic pain, and the Neuropathic Pain Symptom Inventory (NPSI) to assess the intensity of the various qualities of neuropathic pain. All patients underwent a standard nerve conduction study (NCS) to assess the function of non-nociceptive Aβ-fibres, and the cutaneous silent period (CSP) after stimulation of the IIIrd and Vth digits, to assess the function of nociceptive Aδ-fibres. In 40 patients (75 CTS hands) we also recorded laser-evoked potentials (LEPs) in response to stimuli delivered to the median nerve territory and mediated by nociceptive Aδ-fibres. We sought possible correlations between neurophysiological data and the various qualities of neuropathic pain as assessed by the NPSI.

We found that the median nerve sensory conduction velocity correlated with paroxysmal pain and abnormal sensations, whereas LEP amplitude correlated with spontaneous constant pain.

Our findings suggest that whereas paroxysmal pain and abnormal sensations reflect demyelination of non-nociceptive Aβ-fibres, spontaneous constant pain arises from damage to nociceptive Aδ-fibres.

Keywords: Neuropathic pain, Laser-evoked potentials, Carpal tunnel syndrome, Standard nerve conduction study