Laser evoked potential: Analysis of the methodology in post herpetic neuralgia

Background: Selective activation and the contemporary recording of A delta and C fibers from Yap laser on the scalp is a new neurophysiological assessment, allowing the selective activation of the nociceptive system. Objectives: To evaluate if the damage of the nociceptive system was related to post herptic nevralgia (PHN) development in a sample of 26 patients affected by Herpes zooster (HZ); secondly to assess if the impairment of thermal pathway and PHN development were related. Methods: Thirty-two patients were selected for the study, 26 of these were included in the study, whereas 6 were excluded because of cognitive impairment. All 26 study patients were submitted to LEP analysis at baseline (T0) and after six months (T1), and the correlation between clinical thermal disease and the development of PHN was monitored. Results: Pain duration was evidenced by the presence or absence of an instrumental signal in patients with acute HZ infection. There was total concordance between the absence of LEP signal and pain duration. The concordance between the clinical thermal disease and the pain duration was statistically significant for 43% of the sample. Conclusions: Our results suggested a possible role of LEP for PHN prognosis estimation; indeed, most patients affected by acute HZ, with absence of instrumental LEP signal had pain > 6 months. We also noted a significant (43% of cases) clinical concordance between the thermal pathway damage, the absence of instrumental signal and PHN development. Further studies are needed to address this issue.