Use of 5% lidocaine medicated plaster to treat localized neuropathic pain secondary to traumatic injury of peripheral nerves

Neuropathic pain (NP) originates as a direct consequence of injury or illness affecting the somatosensory system.1 Tending to be more persistent than nociceptive pain and with greater cognitive modulation, it results from a stimulus that would not normally provoke pain and responds only to specific medications.2 NP is generally severe, negatively affects patients’ quality of life, and is associated with co-morbidities, such as sleep disturbance, anxiety, depression, and disability.3 NP may occur following nerve injuries, including those from trauma and post-surgical complications.2,4 When this occurs after peripheral nerve injury, it is characterized by spontaneous pain in areas of hyposensitivity and/or hypersensitivity, even in patients who show only very slight changes in their neurological examination results.5 In 1999, the US Food and Drug Administration approved the use of 5% lidocaine medicated plaster (LMP) as the first line of medication for treating allodynia generated by post-herpetic neuralgia.6 It is a topical peripheral noninvasive analgesic with minimal systemic absorption, has a low risk of interacting with other medications, possesses an excellent safety and tolerability profile, and has minimal side effects. Since then, LMP has been incorporated in numerous treatment recommendations in the USA,7 Europe,8 and Latin America,9,10 where it is presented as the first line of treatment for localized peripheral neuropathic pain. This may be defined as “a type of neuropathic pain that is characterized by consistent and circumscribed area(s) of maximum pain.”11 The LMP is applied over the area of maximum pain for 12 hours, without the need for titration. This is followed by a 12-hour interval before the next 12-hour application. Clinical studies have shown that a rest period between plaster usage reduces cutaneous exposure and avoids local secondary effects due to occlusion of the affected skin, but nevertheless produces continuous 24-hour analgesia.12,13 The small amount of lidocaine that passes from the plaster into the skin is sufficient to reduce pain by stabilizing the membrane and blocking pathological activity from sodium channels in altered nerve fibers. This is achieved without anesthetic effect because the amount absorbed does not block the larger myelin fibers.14 The LMP has a “number needed to treat” of 4.4, with a high grade of efficacy in alleviating peripheral NP. Also, the number of patients who need to be treated for one to suffer an intolerable adverse effect (“number needed to harm”) is not significant, being greater than 20.8 Around 40% of patients report pain relief after the second week of use, increasing to 60% by the fourth week of therapy.15,16 The objective of the present study is to complement previous findings and add greater specificity by evaluating the effectiveness and safety of the 5% LMP in patients with chronic, localized, post-traumatic or post-surgical NP in whom peripheral nerve damage has been clearly diagnosed.