Reduction of painful area as new possible therapeutic target in post-herpetic neuropathic pain treated with 5% lidocaine medicated plaster: a case series

Roberto Casale,1,2 Maria Di Matteo,3,7 Cristina E Minella,4,7 Guido Fanelli,5,7 Massimo Allegri4,6,71Department of Clinical Neurophysiology and Pain Rehabilitation Unit, Foundation Salvatore Maugeri, IRCCS, Pavia, 2EFIC Montescano School, Montescano, 3Anesthesia and Intensive Care I, 4Pain Therapy Service, Fondazione IRCCS Policlinico San Matteo, Pavia, 5Department of Anesthesia, Intensive Care and Pain Therapy, Azienda Ospedaliera Universitaria Parma, University of Parma, Parma, 6Department of Clinical, Surgical, Diagnostic and Pediatric Science, University of Pavia, Pavia, 7Study In Multidisciplinary Pain Research Group, Parma, ItalyAbstract: Post-herpetic neuralgia (PHN) is neuropathic pain persisting after an acute episode of herpes zoster, and is associated with severe pain and sensory abnormalities that adversely affect the patient's quality of life and increase health care costs. Up to 83% of patients with PHN describe localized neuropathic pain, defined as “a type of neuropathic pain characterized by consistent and circumscribed area(s) of maximum pain”. Topical treatments have been suggested as a first-line treatment for localized neuropathic pain. Use of 5% lidocaine medicated plaster could reduce abnormal nervous peripheral discharge and via the plaster could have a “protective” function in the affected area. It has been suggested that use of this plaster could reduce pain as well as the size of the painful area. To evaluate this possible outcome, we retrospectively reviewed eight patients with PHN, treated using 5% lidocaine medicated plaster. During a follow-up period of 3 months, we observed good pain relief, which was associated with a 46% reduction in size of the painful area after one month (from 236.38±140.34 cm2 to 128.80±95.7 cm2) and a 66% reduction after 3 months (81.38±59.19 cm2). Our study cohort was composed mainly of elderly patients taking multiple drugs to treat comorbidities, who have a high risk of drug–drug interactions. Such patients benefit greatly from topical treatment of PHN. Our observations confirm the effectiveness of lidocaine plasters in the treatment of PHN, indicating that 5% lidocaine medicated plaster could reduce the size of the painful area. This last observation has to be confirmed and the mechanisms clarified in appropriate larger randomized controlled trials.Keywords: localized neuropathic pain, topical treatment, chronic pain, drug–drug interactions, patient's outcome