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

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 cm(2) to 128.80±95.7 cm(2)) and a 66% reduction after 3 months (81.38±59.19 cm(2)). 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.