Mechanisms of neuropathic pain in patients with Charcot-Marie-Tooth 1 A: A laser-evoked potential study

Charcot-Marie-Tooth (CMT) disease is the most common inherited neuropathy. The CMT1A type can be considered the typical phenotype of this disease. Although pain is not considered a relevant symptom in CMT patients by physicians and no study assessed it comprehensively, this symptom is frequently complained by patients. The objective of the present study was to investigate the nociceptive system in a sample of CMT1A patients suffering from pain by laser-evoked potentials (LEPs). Moreover, we also used a pain specific questionnaire in order to obtain patient-oriented data about their painful symptoms, the Neuropathic Pain Diagnostic Questionnaire (DN4). We evaluated 16 patients affected by CMT1A and 14 controls. All subjects underwent a standard LEP recording session (foot, hand, and face stimulation) and filled in the DN4. While the N2/P2 amplitude to foot stimulation was lower in CMT patients than in controls (p = 0.003), no difference in LEP amplitude to both hand and face stimulation was found between patients and healthy subjects (p > 0.05). This result is probably due to a length-dependent Aδ-fiber loss which involves mostly the longer fibers coming from the lower limb. In our patients, there was a significant association between a reduced N2/P2 amplitude to foot stimulation and a high DN4 score (p = 0.03), meaning that patients with highly probable neuropathic pain had also low N2/P2 amplitude values to painful foot stimulation. This suggests that in our CMT1A patients neuropathic pain is probably related to a reduction of the Aδ afferents.