A Randomized Controlled Trial of Lidocaine Patch for Lower Limb Amputation Pain

Phantom limb pain (PLP) and scar hyperalgesia (SH) are frequent problems after amputation; in particular most persons who undergo limb amputation will experience phantom pain. The neuropathic nature of PLP suggests the involvement of both peripheral and central neurological mechanisms, including neuroplastic changes in the central nervous system. PLP as other central nervous system-related pain syndromes remains a challenge for treatment. Scar hyperalgesia involves peripheral mechanisms and results frim the production of substances liberated by damaged skin cells. These inflammatory substances lower the pain threshold by altering the chemical environment of skin nerve endings. Scan hyperalgesia is associated with secondary mechanical hyperalgesia in the skin area around the scar.

The lidocaine patch 5% is a topical analgesic acting by blocking sodium channels of peripheral nerve endings and by inhibiting ectopic discharges in sensitized and hyperactive cutaneous nociceptors. The patch is noninvasive, with minimal systemic absorption resulting in a reduced risk of drug-drug interaction. In addition, a central analgesic effect of lidocaine has been suggested. The lidocaine patch 5% is currently licensed for the treatment of symptomatic postherpetic neuralgia. It also has been successfully used in patients with other neuropathic pain states, such as entrapment neuropathies, painful idiopathic distal sensory polyneuropathies and postoperative/post traumatic neuropathic chronic cutaneous pain. The lidocaine patch has not been studied for the management and prevention of phantom limb pain.

The aim of the present research is to investigate if a lidocaine patch 5% is effective for reducing PLP and primary/secondary scar hyperalgesia. The hypothesis is that persistent peripheral nociceptive input from the stump after surgery may drive maladaptive cortical reorganization leading to chronic central pain and thus promote chronic phantom limb pain. Treating scar hyperalgesia on the stump with topical lidocaine may reduce the activity of peripheral nociceptive afferents and thus decrease the likelihood of developing persistent phantom limb pain.

This study is designed as a randomized controlled multicentric double blind trial, in which the effectiveness of applying a 5% lidocaine patch for 6 weeks will be compared with a sham.