RESPONSE TO IV LIDOCAINE PREDICT FAVORABLE RESPONSE TO ORAL MEXILETIE

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Phantom Limb pain and stump pain are common post-amputation sequela. Most recent studies estimate 50-75% of amputees suffer from phantom pain early after amputation. Persistent phantom pain is difficult to treat and often worsens over time. Stump pain is less common and often decreases with time. we determined the efficacy of intravenous lidocaine and morphine infusions as compared to placebo on phantom and stump pain after amputation of extremities using a double-blind randomized protocol. Six patients (2 F and 4 M) were enrolled between 12/01/97 and 11/30/98 following approval by the institutional investigational review board. Exclusion criteria included age <18 or >90, cardiac conduction defects, myocardial infarction within 6 months, severe pulmonary, hepatic, or hematologic disease, and history of seizures, dementia, or encephalopathy. In a double blind fashion, an intravenous bolus followed by an infusion of lidocaine (5mg/kg), or morphine (0.25mg/kg), or diphenhydramine (25mg) were administered over 30 minutes. Phantom and/ or stump pain, and pain evoked by a brass probe over the sensitive region of the stump were recorded at 5 minute intervals starting 30 minutes prior to bolus dose and continued 30 minutes after the end of infusion. The drun-induced change in pain scores were compared to preinfusion baseline pain scores. Phantom pain scores were decreased by lidocaine (range = 4.50% - 68.40%) in all 5 patients tested, and by morphine (range = 1.46% - 39%) in 4 out of 5 patients tested. One of the patients did not respond to morphine infusion. Only 2 out of 5 patients tested responded to diphenhydramine placebo infusion (range = 2%-4.77%). Stump pain scores were decreased by lidocaine (range = 23.50% - 100%), and by morphine (range = 13.76% - 67.63%) in all 6 patients tested. Only 3 out of 6 patients tested reported stump pain relief (ranges = 0.49% - 10.75%) to diphenhydramine placebo infusion.