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

Abstract

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.

The 5% Lidocaine-Medicated Plaster: Its Inclusion in International Treatment Guidelines for Treating Localized Neuropathic Pain, and Clinical Evidence Supporting its Use

“…Therefore, one contributory factor to the improved QoL scores is likely to be the reduction in the area of allodynia—typically more than 50% [59, 60]—produced by treatment with the lidocaine plaster. Reducing the painful area, which can increase tolerance of bathing and contact with clothing, is therefore a justifiable treatment goal for this medication.…”

“…It was generally felt that existing guidelines were of limited use in determining treatment for LNP, because most do not specifically address this condition—or even recognize it as a specific entity—and recommendations of the different guidelines are not consistent [15]. Board members strongly agreed that the first-line treatment—irrespective of age—should be a topical analgesic agent in most cases unless there are contraindications such as broken, atrophic, or infected skin—essentially because the topical route offers a far better safety profile [16, 17] and there is evidence that it can reduce the size of the painful area [58–60]. Factors influencing the choice of topical agent should include ease of application and use, patient preference, and availability [15], but the 5% lidocaine-medicated plaster currently has the most evidence supporting its use in treating LNP.…”

“…A recent study by Casale et al comprised a case series of elderly patients with PHN who were receiving one or more systemic drugs, but whose pain was inadequately controlled or who had good pain control but were experiencing severe side effects [60]. The 5% medicated plaster was prescribed in addition to their systemic medication and they were followed up for 3 months.…”

“…The 5% medicated plaster was prescribed in addition to their systemic medication and they were followed up for 3 months. Effective pain relief began as early as 2 weeks after the commencement of topical treatment and steadily increased, reaching 52.00 ± 23.87% after 4 weeks and 60.00 ± 18.70% after 12 weeks [60]. Notably, the area of allodynia progressively decreased from baseline, with a reduction of 46% after 1 month ( p  = 0.129) and 66% after 3 months ( p  = 0.02), enabling patients to apply fewer and smaller plasters [60].…”

“…Effective pain relief began as early as 2 weeks after the commencement of topical treatment and steadily increased, reaching 52.00 ± 23.87% after 4 weeks and 60.00 ± 18.70% after 12 weeks [60]. Notably, the area of allodynia progressively decreased from baseline, with a reduction of 46% after 1 month ( p  = 0.129) and 66% after 3 months ( p  = 0.02), enabling patients to apply fewer and smaller plasters [60]. The authors suggest these results indicate a possible role for long-term treatment with the lidocaine plaster to reduce the painful area affected by LNP, although further research is needed [60].…”