Continuous brachial plexus analgesia and NMDA-receptor blockade in early phantom limb pain: a report of two cases.

OBJECTIVE: To provide a mechanism-based acute pain management strategy for early phantom limb pain following traumatic amputations and to collect first evidence of its acute and potentially preventative effects on the formation and maintenance of phantom limb pain. The combination of continuous brachial plexus analgesia and prolonged block of N-methyl-D-aspartate (NMDA) receptors over 4 weeks aimed to attenuate peripheral and central sensitization, currently thought to be substantially involved in establishing and maintaining phantom limb pain. CASE REPORT: Two patients, after traumatic upper limb amputations and early phantom limb pain, were treated on the second and fifth day following amputation by continuous brachial plexus analgesia with ropivacaine 0.375% (30 ml for the initial block, continuous infusion rate = 5 ml/h) for 5 (Patient 1) and 9 days (Patient 2). Both patients received oral memantine (a noncompetitive NMDA-receptor antagonist) in increasing doses from 10 to 30 mg/d over a 4-week period. Ropivacaine only produced minor motor block, with almost unimpaired motor function. Memantine was well tolerated and no relevant side effects were observed. In both patients the treatment prevented the establishment of phantom limb pain, which did not reappear during follow-up of 1 year.
CONCLUSIONS: The combination of long-term regional analgesia with prolonged block of NMDA receptors might be effective for treatment and prevention of phantom limb pain following traumatic amputations. The absence of clinically relevant side effects, together with maintained motor function suggests this treatment to be a promising preventive strategy for phantom limb pain following traumatic amputations.